Vol.1 N.1 - Journal of Aerospace Technology and Management by Journal of Aerospace Technology and Management

Journal of Aerospace Technology and Management J. Aerosp. Technol. Manag. Volume 01, Nº 01, Jan. - Jun. 2009

EDITOR IN CHIEF Francisco Cristóvão Lourenço de Melo Institute of Aeronautics and Space (IAE) São José dos Campos, SP, Brazil

ASSOCIATE EDITORS

EDITORIAL PRODUCTION

Adriana Medeiros Gama Ana Cristina Avelar Antonio Pascoal Del' Arco Junior Christian Giorgio Roberto Taranti Cynthia Cristina Martins Junqueira Elisabeth da Costa Mattos Jorge Carlos Narciso Dutra Roberto Roma de Vasconcelos Vinícius André Rodrigues Henriques Waldemar de Castro Leite

Alessandra Mendes David Ana Cristina Camargo Sant'Anna Ana Marlene Freitas de Morais Carla Alexandra Gallegos Levon Delma Felício Doralice da Cunha Glauco da Silva Helena Prado de Amorim Silva Lais Maria Resende Mallaco Márcia Maria Ernandes Robles Fracasso

EDITORIAL BOARD Acir Mércio Loredo-Souza - Federal University of Rio Grande do Sul - Porto Alegre - Brazil Adolfo Gomes Marto - Institute of Aeronautics and Space - São José dos Campos - Brazil Alain Azoulay - Superior School of Eletricity - Paris - France Alexandre Garcia - Institute of Aeronautics and Space - São José dos Campos - Brazil Amilcar Porto Pimenta - Technological Institute of Aeronautics - São José dos Campos - Brazil Antonio Eduardo Carrilho da Cunha - Military Institute of Engineering - Rio de Janeiro - Brazil Avandelino Santana Jr. - Institute of Aeronautics and Space - São José dos Campos - Brazil Bert Pluymers - Catolic University of Leuven - Leuven - Belgium Carlos Alberto Alves Cairo - Institute of Aeronautics and Space - São José dos Campos - Brazil Carlos de Moura Neto - Technological Institute of Aeronautics - São José dos Campos - Brazil Clésio Luis Tozzi - State University of Campinas - Campinas - Brazil Cosme Roberto Moreira da Silva - University of Brasília - Brasília - Brazil Edílson Alexandre Camargo - Institute of Aeronautics and Space - São José dos Campos - Brazil Edson Aparecido de A. Querido Oliveira - University of Taubaté - Taubaté - Brazil Edson Cocchieri Botelho - São Paulo State University - Guaratinguetá - Brazil Edson Luis Zaparoli - Technological Institute of Aeronautics - São José dos Campos - Brazil Enda Dimitri Bigarella - Embraer - São José dos Campos - Brazil Fabrice Burel - National Institute of Applied Sciences - Lion - France Fausto Ivan Barbosa - Technological Institute of Aeronautics - São José dos Campos - Brazil Fernanda M. B. Coutinho - State University of Rio de Janeiro - Rio de Janeiro - Brazil Flavio Araripe D'Oliveira - Institute of Aeronautics and Space - São José dos Campos - Brazil Francisco Carlos P. Bizarria - Institute of Aeronautics and Space - São José dos Campos - Brazil Journal of Aerospace Technology and Management

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Francisco Piorino Neto - Institute of Aeronautics and Space - São José dos Campos - Brazil Frederic Plourde - Superior National School of Mechanics and Aerotechnics - Poitiers - France Fernando Luiz Bastian - Federal University of Rio de Janeiro - Rio de Janeiro - Brazil Gilberto Fish - Institute of Aeronautics and Space - São José dos Campos - Brazil Gilmar Patrocinio Thim - Technological Institute of Aeronautics - São José dos Campos - Brazil Gilson da Silva - National Industrial Property Institute - Rio de Janeiro - Brazil João Amato Neto - University of São Paulo - São Paulo - Brazil João Batista Pessoa Falcão Filho - Institute of Aeronautics and Space - São José dos Campos - Brazil João Luiz Filgueiras Azevedo - Institute of Aeronautics and Space - São José dos Campos - Brazil João Marcos Travassos Romano - State University of Campinas - Campinas - Brazil João Pedro Escosteguy - Institute of Aeronautics and Space - São José dos Campos - Brazil Joern Sesterhenn - University of Munich - Munich - Germany Johannes Quaas - Max Planck Institute for Meteorology - Hamburg - Germany José Alberto Fernandes Ferreira - University of Taubaté - Taubaté - Brazil José Atílio Fritz Fidel Rocco - Technological Institute of Aeronautics - São José dos Campos - Brazil José Henrique de Sousa Damiani - Technological Institute of Aeronautics - São José dos Campos - Brazil Koshum Iha - Technological Institute of Aeronautics - São José dos Campos - Brazil José Maria Fonte Ferreira - University of Aveiro - Aveiro - Portugal Luciene Dias Villar - Institute of Aeronautics and Space - São José dos Campos - Brazil Luis Carlos de Castro Santos - Embraer - São José dos Campos - Brazil Luiz Claudio Pardini - Institute of Aeronautics and Space - São José dos Campos - Brazil Luis Augusto Toledo Machado - National Institute for Space Research - Cachoeira Paulista - Brazil Luis Eduardo Loures da Costa - Institute of Aeronautics and Space - São José dos Campos - Brazil Luis Fernando Figueira da Silva - Pontifical Catholic University - Rio de Janeiro - Brazil Márcio da Silveira Luz - General Command for Aerospace Technology - São José dos Campos - Brazil Márcio Teixeira de Mendonça - Institute of Aeronautics and Space - São José dos Campos - Brazil Marcos Aurélio Ortega - Technological Institute of Aeronautics - São José dos Campos - Brazil Marcos Daysuke Oyama - Institute of Aeronautics and Space - São José dos Campos - Brazil Maria Filomena F. Ricco - General Command for Aerospace Technology - São José dos Campos - Brazil Maria Luisa Gregori - Institute of Aeronautics and Space - São José dos Campos - Brazil Maurizio Ferrante - Federal University of São Carlos - São Carlos - Brazil Michael Gaster - University of London - London - UK Michelle Leali Costa - Fastline - São Paulo - Brazil Mirabel Cerqueira Resende - Institute of Aeronautics and Space - São José dos Campos - Brazil Paulo Varoto - São Carlos School of Engineering - São Carlos - Brazil Pedro José de Oliveira Neto - Institute of Aeronautics and Space - São José dos Campos - Brazil Renato Felix Nunes - Institute of Aeronautics and Space - São José dos Campos - Brazil Rita de Cássia Lazzarini Dutra - Institute of Aeronautics and Space - São José dos Campos - Brazil Rogério Pirk - Institute of Aeronautics and Space - São José dos Campos - Brazil Sergio Frascino M. de Almeida - Technological Institute of Aeronautics - São José dos Campos - Brazil Sérgio Henrique da Silva Carneiro - Brazilian Air Force - Brasília - Brazil Takashi Yoneyama -Technological Institute of Aeronautics - São José dos Campos - Brazil Tessaleno Devezas - University of Beira Interior - Covilha - Portugal Ulrich Teipel - University of Nuremberg - Nuremberg - Germany Vassilis Theofilis - Polytechnic University of Madrid - Madrid - Spain

Journal of Aerospace Technology and Management

V. 1, n. 1, Jan. - Jun. 2009

ISSN 1984-9648

Journal of Aerospace Technology and Management Vol. 01, Nº 01, Jan. - Jun. 2009

TABLE OF CONTENTS EDITORIAL 5

The scientific knowledge dissemination under threat Pantoja, F. C. M. REVIEW ARTICLES

Titanium production for aerospace applications Henriques, V. A. R.

Historical review and future perspectives for Pilot Transonic Wind Tunnel of IAE Falcão Filho, J. B. P., Avelar, A. C., Reis, M. L. C. C. TECHNICAL PAPERS

Otimização do processo de obtenção do pré-polímero metil azoteto de glicidila Optimization of the process to obtain glycidyl azide polymer Sciamareli, J., Da Costa, J. R., Takahashi, M. F. K., Iha, K., Berdugo, A. A. V., Diniz, M. F., Miyano, M. H., Ferreira, C.

Synthesis and characterization of energetic thermoplastic elastomers for propellant formulations Kawamoto, A. M., Oliveira, J. I. S., Dutra, R. C. L., Rezende, L. C., Keicher, Th., Krause, H.

Rheology of suspensions with aluminum nano-particles Teipel, U., Forte-Barth, U.

Resistência ao cisalhamento Iosipescu em compósitos de fibra de carbono e de vidro com resina epóxi Iosipesco shear resistance in composites of carbon and glass fiber with epoxi resin Gonçalves, V. O., Pardini, L. C., Garcia, K., Ancelotti, A. C., Bezerra, E. M.

Avaliação de agente de ligação aziridínico por meio de técnicas de análise química e instrumental Evaluation of aziridine bonding agent by means of chemical and instrumental techniques of analysis Pires, D. C., Kawamoto, A. M., Sciamareli, J., Mattos, E. C., Diniz M. F., Dutra, R. C. L., Iha, K.

Ablative and mechanical properties of quartz phenolic composites Gregori, M. L., Barros, E. A., Petraconi Filho, G., Pardini, L. C., Costa, S. F.

Control of Reynolds number in a high speed wind tunnel Silva, M. G.; Gamarra, V. O. R.; Koldaev, V.

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Avaliação do voo tecnológico XVT02 do Veículo Lançador de Satélites VLS-1 por meio de decisão em grupo Evaluation of the technological flight XVT02 of the Satellite Vehicle Launcher VLS-1 by means of group decision Salgado, M. C. V.; Belderrain, M. C. N., Silva, A. C. S. COMMUNICATIONS

Studies using wind tunnel to simulate the Atmospheric Boundary Layer at the Alcântara Space Center Marinho, L. P. B., Avelar, A. C., Fisch, G., Roballo, S. T., Souza, L. F., Gielow, R., Girardi, R. M.

Propulsão líquida no IAE: Visão das atividades e perspectivas futuras Liquid Propulsion at IAE: Vision of the activities and future perspectives Torres, M. F. C., Almeida, D. S., Krishna, Y. S. R., Silva, L. A., Shimote, W. K.

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Brazilian Air Force aircraft structural integrity program: An overview Mello Jr., A. W. S., Mattos, D. F. V., Ribeiro, F. N.

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F-5M DTA Program Mattos, D. F. V., Mello Jr., A. W. S., Ribeiro, F. N. THESIS ABSTRACTS

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Characterization and quantification by FT-IR, HPLC and TG techniques of polymers used in plastic bonded explosive Mattos, E. C.

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Implementation of radial basis function networks on CMOS and BiCMOS technology Lucks, M. B.

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Characterization of thermostructural materials based on carbon reinforced with carbon fibers (CRFC) and carbons modified with silicon carbide (SiC) Gonçalves, A.

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Fluid-structure coupling on unstable vortex shedding phenomena in confined chamber Nunes, R. F.

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Evaluation and modeling of porosity type defects in solid propellant grains Macera, S.

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Ablative carbon-phenolic composites additivated with carbon nanoparticles Pontarolli, M. L.

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Proposal of a risk management method for use during rocket development projects in the Brazilian Air Force Institute of Aeronautics and Space Silva Jr., A. O.

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Application of the ammonium perchlorate particle packing study, and the use of a model for optimizing high performance composite propellant formulations based on HTPB and aluminum Silva, M. C. C.

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Evaluation of the applicability of FT-IR and thermal analysis techniques to the characterization and elastomer quantification Sanches, N. B.

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Dependability requirements analysis process for space software Romani, M. A. S. INSTRUCTIONS TO AUTHORS

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Francisco Carlos Melo Pantoja Director of Institute of Aeronautics and Space SĂŁo JosĂŠ dos Campos - Brazil diretor@iae.cta.br

Editorial The scientific knowledge dissemination under threat

I feel very proud to have been invited to write the editorial for the first issue of the Journal of Aerospace Technology and Management. Although this is the first time I have written a column like this, it is not the first time I have thought about issues related to aerospace technology and management. As the current Director of the Institute of Aeronautics and Space, I have been thinking along these lines for quite some time. Since the Institute mission includes knowledge production and development of technology, one of our concerns, as expected, is the understanding of the many faces of science-technology relationship. Throughout history the interaction between science and technology has been persistently analyzed and various models have been proposed which try to explain this relationship from different points of view. In some of these descriptions it is assumed that it is the scientific research that provides the underlying foundation of knowledge needed to enable breakthrough technology. Another description considers that, throughout history, the flow has also gone from technology to science. As an example of the latter we have the development of the telescope by Galileo. This new instrument led to better astronomical measurements, which rendered the prevailing theory of an earth-centered universe so complex, that it led to the significantly simpler idea of a sun-centered universe. We may also reflect on the science-technology relationship taking into account the interactions among the main protagonists involved in these processes: universities, research centers and industry. In The United States, during the 1980s, universities were blamed for their ineffective participation in industrial competitiveness. At that time, it was argued that universities had a civic duty to ally themselves closely with industry to improve productivity. This started a kind of partnership rush and since then we have seen a significant rise in the level of collaboration between the private commercial sector, research centers and universities. Good examples are the classic success stories of Stanford University and Silicon Valley in California, and the Massachusetts Technology Institute and the Route 128 beltway around Boston clusters of cutting-edge computing technology. However, this also caused concerns among academic officials that greater involvement of universities with industry would promote a shift from fundamental science to more applied work. At first glance, this collaboration model seems to be a good example of a win-win strategy. We easily realize everywhere the strong and enduring policy consensus that presently favors scientific knowledge production, mainly in the form of direct subsidies for national industrial development. This practice has been viewed as the most important way of achieving innovation. In this conceptual model, the focus of the research efforts in both universities and research centers is almost entirely product-related. Although there is nothing wrong with policies that encourage joint development, since it happens to be good in many ways, this practice may have gone too far and we are running the risk of distracting the universities and research centers from their major responsibilities towards society. Research priorities should not be settled by financial interests, and research results should be made available to the public as a whole. This excessive partnership between scientific institutions and industry affects research, teaching, funding, ethics, scientific publications and many other important areas in the science-technology relationship. Presently, we have seen many universities changing their curriculum to adapt it to the demands of industry. This state of affairs also involves growing secrecy in academic research fuelled by industrial competitiveness. This increased confidentiality contradicts the need for the open dissemination of scientific knowledge without necessarily being concerned about commercial viability. But the real problem is that these confidentiality agreements, also called disclosure restrictions, that govern what can be published, threaten the efficient advancement of scientific frontiers. We turn next to another risk to be considered regarding the dissemination of scientific knowledge. The first scientific journals were the French Journal des SĂ§avans and the British Philosophical Transactions, both published in the year 1665. Journal of Aerospace Technology and Management

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Since then, publishing journals has become a key activity of learned academies and professional societies. Over time, investors saw an opportunity for business and profit, and these journals emerged as businesses with very high profit margins. Many professional societies handed their journal publishing activity over to commercial publishing houses, which not only started imposing huge subscription prices for the journals they produced, but also started 'bundling', a practice by which subscribing libraries are made to buy a large number of journals not all of which may be found useful by their clients. In the past two decades, average journal subscription prices have increased considerably. Scientific research is a community activity. In science, as a general rule, no one can claim to be an autonomous creator. One's thoughts and ideas are shaped by the literature one is exposed to, the talks one hears at conferences one attends, and the discussion one holds with other scientists in formal and often informal settings. The Journal of Aerospace Technology and Management is a tool intended to reinforce this point of view. It is a free publication and an additional source of dissemination and interaction for the scientific community. It is going to be published every six months and its main objective is to show the results of scientific and technological research, especially those related to the aerospace field. The classic relationship between science and technology holds that science is a body of truths about nature and technology the practical application of these truths in the production of useful devices and systems. Especially in a capitalist system, truth and utility belong to different worlds. Today, faced with repeated market collapses, the world economy can no longer afford investments in â&#x20AC;&#x153;pure researchâ&#x20AC;?, because it does not produce a rapid return on capital. Ironically, in the long run, this increased constraint on science, especially as regards basic research development, undermines the economic and social viability of the capitalist system itself. Developing nations are at particular risk from these trends. Indeed, as many have pointed out, the growing privatization of scientific knowledge is widening the knowledge gap between rich and poor countries. Lastly, I do believe in the benefits of the synergic relationship between the academic and industrial communities, but it is necessary to perceive that urgent measures should be taken to redress the balance between public access to, and private control over, scientific knowledge. Like fuel, oxygen and heat and their cooperation to produce fire, the universities, research centers and industry, likewise, should work together without losing their individual character to be able to meet society's needs not only for present but for future generations as well. Enjoy the read!

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Vinicius A. R. Henriques* Institute of Aeronautics and Space São José dos Campos - Brazil vinicius@iae.cta.br

*author for correspondence

Titanium production for aerospace applications Abstract: Titanium parts are ideally suited for advanced aerospace systems because of their unique combination of high specific strength at both room temperature and moderately elevated temperature, in addition to excellent general corrosion resistance. The objective of this work is to present a review of titanium metallurgy focused on aerospace applications, including developments in the Brazilian production of titanium aimed at aerospace applications. The article includes an account of the evolution of titanium research in the Brazilian Institute (IAE/CTA) and the current state-of-art of titanium production in Brazil. Key words: Titanium, Aerospace industry, Powder metallurgy.

INTRODUCTION Over the last decade, the focus of titanium alloys development has shifted from aerospace to industrial applications. However, the titanium industry continues to depend on the aerospace market and this sector will constitute a significant percentage of total consumption for years to come. The metallurgy of titanium and Ti-base alloys has been intensely researched over the last 50 years. Titanium has unique properties such as its high strength-toweight ratio, good resistance to many corrosive environments and it can be used over a wide range of temperatures. Typical engineering applications of titanium alloys include the manufacture of cryogenic devices and aerospace components. The high buy-to-fly ratio associated with many titanium components, combined with forging and machining difficulties, has led to a strong drive for nearnet titanium manufacture. A very promising method of attaining this goal is powder metallurgy (P/M) (Froes, 1980). The primary justifications for using titanium in the aerospace industry are (Boyer, 1994):

Titanium could also replace aluminum when the operating temperature exceeds around 130C, which is the normal maximum operating temperature for conventional aluminum. These conditions exist, for example, in the nacelle and auxiliary power unity (APU) areas and wing anti-icing system for airframe structures. Steel and nickelbased alloys are obvious alternatives, but they have a density about 1.7 times that of titanium (Andersen, 1980, Donachie, 1988). Corrosion resistance can be a very important issue. The corrosion resistance of titanium is such that corrosion protective coatings or paints are not required: (paint is applied when titanium comes into contact with aluminum or low alloy steel components to prevent galvanic corrosion of the contact material). Much of the floor support structure under the galleys and lavatories is in a very corrosive environment that dictates the use of titanium to provide high structural durability (Andersen, 1980).

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Polymer matrix composite (PMC) compatibility is becoming a bigger issue with increased use of composite structures on aircraft. Titanium is galvanically compatible with the carbon fibers in the composites, whereas aluminum (and low alloy steels) and carbon generate a significant galvanic potential. The choice of titanium in these instances is related to the criticality of the structure (Boyer, 1994).

Weight savings are due to the high strength-to-weight ratio. The lower density of titanium compared with steel permits weight savings, replacing steels even though they may be higher strength. As the strength of titanium alloys is significantly higher than Al alloys, weight savings can be achieved when they their replace aluminum despite the 60 per cent higher density, assuming that the component is not gage limited (Allen, 1996).

Titanium is not as widely used as aluminum or steel but it is not a rare or precious metal. Titanium is the fourth most abundant metal in the earth's crust (0.86 per cent by weight) after aluminum, iron, and magnesium. However, titanium is difficult to extract from its core, difficult to process, and difficult to manufacture. Just accounting for the extraction and processing costs to produce an ingot, titanium is ~30 times more expensive than steel and ~6 times the cost of aluminum (Hurless, 2002).

weight savings (primarily as a steel replacement); space limitation (replace Al alloys); operating temperature (Al, Ni, steel alloys replacement); corrosion resistance (replace Al and low alloy steels); and  composite compatibility (replace Al alloys).

____________________________________ Received: 05/05/09 Accepted: 26/05/09

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Historically, titanium has experienced anemic growth when compared with aluminum and stainless steel alloys. V. 1, n. 1, Jan. - Jun. 2009

Henriques, V.A.R.

The high cost of production limited the use of titanium to applications requiring high performance or where life cycle cost analyses justified its use. The aerospace and defense communities stimulated initial development of titanium alloys in the early 1950s. Aircraft development during the Cold War was performance-driven without much regard to cost. A radical example of this was the SR-71 Blackbird reconnaissance aircraft, with over 90 per cent of the structure being titanium (Hurless, 2002). The growth potential and cost-cutting initiatives of titanium were severely limited by the dependence upon the cyclic nature of the aerospace industry, with the market experiencing 4-5 year cycles of boom and bust. During boom periods, users were only interested in rapid access to materials, leaving reduced time for development of low cost techniques; bust periods had few resources available for low cost techniques (Hurless, 2002). Cost-conscious markets, such as the automotive industry, are reluctant to commit to titanium because of the unpredictability of the cost fueled by the boom and bust economics. However, with world production of 60 million vehicles annually, even 0.5kg of titanium in 50 per cent of the vehicles produced would increase titanium use by 30 per cent, helping to stabilize the cost and reduce dependence on the aerospace industry (Andersen, 1980). Every stage of titanium production except the mining of ore has a tremendous potential impact on the final cost of titanium products. Regarding ore mining, the cost of ore is highly dependent on demand, thus cost reductions will naturally result from a major increase in the demand for titanium products. When considering cost reduction, it is strategic to focus on the early stages of production, where any cost advantages achieved would be carried through all production stages. The cost of extracting titanium from the ore is approximately 20 times that of steel on a 1-to-1 weight basis, but roughly 11 times when accounting for the density advantage of titanium (less titanium would be required to perform the same function as steel) [6]. Beyond that, machining costs for titanium are generally significantly higher than for the other materials (at least 10 times higher than to machine Al). In that sense, titanium alloy production using powder metallurgy (P/M), starting from the elemental or prealloyed powders is a interesting route considering its lower costs, versatility and also the facility it offers to manufacture parts with complex geometry and close to the final dimensions (Henriques 2005, Froes, 1988).

The reduction reaction is carried out in a large retort, in an inert atmosphere, where titanium tetrachloride is sprayed onto a high-temperature reactive surface of molten magnesium. TiCl4 reacts to form a sintered, porous mass of titanium, salt, and unreacted chemicals called “sponge” (Kroll, 1937). After the reaction reaches its equilibrium state, the residual impurities are eliminated by a vacuum distillation stage. One end of the retort is cut off and the sponge is jacked out of the retort. It is then chopped and ground into chips of about one centimeter size. The chips are acid-leached, water-washed, and dried. In the final stage, the chips are compressed and welded into an electrode, which in turn is melted into an ingot in a vacuum arc furnace. Alloys of titanium are formed by adding chips of the alloying elements to the electrode as it is being compressed and welded into an electrode shape. The arc melting removes volatile impurities and improves homogeneity. High purity alloys require an initial melt and two further remelts [Kroll, 1940]. The Kroll process has a number of serious disadvantages [Collings, 1983]: l l l

It is a multi-step process. Each individual step is a batch process. The initial stage operates at high temperature in retorts with short working lifetimes. It produces a sintered product with high levels of impurities. The second stage removes some of the impurities and discharges a polluted waste stream. The purification stage removes the rest of the impurities through multiple melts in high vacuum arc furnaces.

All of these inherent disadvantages add up to a product that is so expensive it can compete with other metals only in very specialized niche markets. Titanium alloys Titanium exists in two crystallographic forms. At room temperature (RT), unalloyed (commercially pure) titanium has a hexagonal close-packed (hcp) crystal structure referred to as alpha (α) phase. At 883°C (1621°F), this transforms to a body-centered cubic (bcc) structure known as beta (β) phase. The manipulation of these crystallographic variations through alloying additions and thermomechanical processing is the basis for the development of a wide range of alloys and properties. These phases also provide a convenient way to categorize titanium mill products (Barksdale, 1966).

The Kroll Process The basic chemical process for titanium production was patented by Wilhelm Kroll in 1938. The Kroll process has four stages: tetrachloride (TiCl4) production, reduction reaction, vacuum distillation, and melt purification. The first step in the process is the preparation of the tetrachloride itself, which is carried out by the chlorination of a mixture of carbon with rutile or ilmenite in a fluidized bed furnace. Journal of Aerospace Technology and Management

There are three titanium alloy types based on the composition of the alloy and the resultant predominant room temperature constituent phase(s), and each of these families of alloys serves a specific role. The alloy types include alpha (α) alloys, alpha (α) + beta (β) alloys and (β) alloys. Alpha is the low temperature allotrope of titanium, and the microstructure consists predominantly of the αphase. Alpha (α) + beta (β) are, for the main part, still mostly V. 1, n. 1, Jan. - Jun. 2009

Titanium production for aerospace applications

α at RT, but they do have more of the β-phase, the high temperature allotrope, than the former class of alloys. The definition of β-alloys is not fully agreed upon, but in very general terms, they are capable of retaining 100 per cent β when quenched from the β-phase field (Leyens, 2003). Alpha alloys contain elements such as aluminum and tin. These α-stabilizing elements work by either inhibiting change in the phase transformation temperature or by causing it to increase. Alpha alloys generally have creep resistance superior to β alloys, and are preferred for hightemperature applications. The absence of a ductile-tobrittle transition, a feature of β alloys, makes α alloys suitable for cryogenic applications. Alpha alloys are characterized by satisfactory strength, toughness, and weldability, but poorer forgeability than β alloys. This latter characteristic results in a greater tendency for forging defects. Smaller reductions and frequent reheating can minimize these problems. Unlike β alloys, alpha alloys cannot be strengthened by heat treatment. They most often are used in the annealed or recrystallized condition to eliminate residual stresses caused by working. Ti-5Al2,5Sn is the most important alloy and it is used for cryogenic applications (Barksdale, 1966). Alpha + beta alloys have compositions that support a mixture of α and β phases and may contain between 10 and 50 per cent β phase at room temperature. The most common α + β alloy is Ti-6Al-4V. Although this particular alloy is relatively difficult to form even in the annealed condition, α + β alloys generally have good formability. The properties of these alloys can be controlled through heat treatment, which is used to adjust the amounts and types of β phase present. Solution treatment followed by aging at 480 to 650°C (900 to 1200°F) precipitates α, resulting in a fine mixture of α and β in a matrix of retained or transformed β phase Ti-6Al-4V is the most widely used titanium alloy and accounts for nearly 45 per cent of total titanium production (Lütjering, 2007). Beta alloys contain transition elements such as vanadium, niobium and molybdenum, which tend to decrease the temperature of the α to β phase transition and thus promote development of the bcc β phase. They have excellent forgeability over a wider range of forging temperatures than α alloys, and β alloy sheet is cold formable in the solutiontreated condition. Beta alloys have excellent hardenability, and respond readily to heat treatment. A common thermal treatment involves solution treatment followed by aging at temperatures of 450 to 650°C (850 to 1200°F). This treatment results in formation of finely dispersed particles in the retained β. Ti-10V-2Fe-3Al is one of the most important β alloys for aerospace applications nowadays (Hanson, 1995, Stephen, 1988). Market Since the attacks on the World Trade Center in September 2001, the titanium industry has been characterized by a steep decline in demand for its use in aerospace applications. Demand for titanium sponge in the USA, the Journal of Aerospace Technology and Management

world's largest market, fell by 34 per cent in 2002, and that for mill products by 30 per cent. The SARS (Severe Acute Respiratory Syndrome) crisis and the Iraq war prevented recovery in 2003 (Lütjering, 2007). However, in the absence of any further catastrophic events impacting directly on commercial airlines, demand for titanium metal is forecast to recover steadily over the next five years. The western world's passenger airline fleet of over 100 seats is expected to increase from 10,800 aircraft in 2004 to over 30,000 in 2020. This growth in demand will be boosted further by the increasing production of military aircraft, particularly with the F22 having probably the highest proportion of titanium of any aircraft, with 39 per cent by weight of titanium (Froes, 2004). Russia, Kazakhstan and Japan dominate sponge production. Supply of titanium sponge is confined to nine producers in six countries. Russia, Kazakhstan and Japan now account for an estimated 75 per cent of world production (Fig. 1), which is around 73000t (Henriques, 2008). The role of Russian group VSMPO-Avisma in the titanium market continues to grow significantly with operational capacity reaching 24000t/year in 2004. A recent link up with Allvac (Allegheny Technologies) has also given them a much better base for selling in the USA, the largest consumer of titanium metal (Seong, 2009).

Figure 1: Market share of titanium sponge production (Seong, 2009).

The high cost of recovery discourages wider use. The use of titanium metal in cars, buildings and medical applications is currently restricted by the high costs of recovery and processing. Development of the FFC Cambridge continuous process for producing titanium sponge, which involves direct electrochemical reduction of TiO2 in fused salt, nowadays, has funding from the US Department of Defense and commercialization appears to be closer. Similarly, other advances in powder metallurgy, laser forming and casting may reduce costs, but the expensive processes required to melt and alloy titanium will continue to reduce its competitiveness. Nevertheless, larger scale output of lower cost titanium and titanium alloy products for V. 1, n. 1, Jan. - Jun. 2009

Henriques, V.A.R.

use in applications with broader tolerances, such as automotive parts and construction, remains a possibility (Rossman, 2007). The use of titanium in aircraft is rising. The main end uses for titanium in aerospace are in compressor blades and wheels, stator blades, rotors, and other parts in aircraft gas turbine engines. The second largest end use is in airframe structures such as landing gear, ducting, wing-carry through structures, weight-and-space-critical forgings, and in structures where resistance to heat is important. The amount of titanium used per aircraft has increased steadily from the historical 10 per cent, with as much as 65t used in each Airbus A380. The price of titanium grew 20 per cent in 2005, causing concern to the manufacturers of aircraft. Sponge producers had decreased production due to the reduction in demand in 2001. With the current growth of titanium use in the sector, prices are rising. The use in other applications such as power stations and desalinization units in China has contributed to the increase in prices (Seong, 2009). Titanium sponge which traditionally sold at 10 dollars/kg reached 30 dollars in 2005, with the price falling to 20 dollars in the middle of the year, later returning to 30 dollars by the end of the year. The development of the 787 Boeing and the Airbus A-380, which use large amounts of titanium, has contributed to the increase in demand. It is supposed that with the stabilization of the production, the trend is to return to normal values up to 2010 (Rossman, 2007, Roza, 2008). Titanium Production in Brazil Studies on metallic titanium production in Brazil were originally developed in the Military Institute of Engineering (IME), in 1965, as a result of undergraduate work, when two small blocks of sponge with about 2 kg each were produced. In the same year, the Brazilian Air Force (MAer) carried out its first study centered on the development of titanium production techniques, not only for use in aircrafts, but also aimed at creating conditions in Brazil for: the consumption of the metal; the exploration of Brazilian ores and the development of a new technology for the treatment with reactive metals. These research activities were pioneering in the use of vacuum equipment for the melting and refining of metals in Brazil, developed in the Materials Division of the Aerospace Institute (AMR/IAE/CTA) (Henriques, 2008). AMR began its work with a view to supplying the needs related to ferrous and non-ferrous materials, used in structural parts of aircraft and rockets (Henriques, 2008). The Metallurgical Processes Group (GPM) was created in 1965 in order to produce reactive metallic alloys, in particular, titanium and zirconium for the aerospace industry. To achieve these objectives, a laboratory with a complete infrastructure for vacuum melting and purification was created, including Vacuum Arc Remelting Journal of Aerospace Technology and Management

(VAR), Vacuum Induction Melting (VIM), Electro-slag and Electron Beam furnaces. This group of equipment was, at that time, the most expensive and capable research center plant in Brazil. The group generated an enormous amount of reports, articles, books and theses. During this time, GPM developed research lines in strategic materials such as zirconium, uranium, magnesium, beryllium, germanium, refractory alloys and especially titanium (Henriques, 2008, Rover, 1971a). These works are of immeasurable importance in the advance of the national research on strategic materials. GPM was a pioneer in the use of vacuum metallurgy for refining metals and for the production of reactive metallic alloys, being the generator of the most important special alloys producer in Brazil, Eletrometal (Henriques, 2008). Historical importance of the Titanium Project All the technology was developed with the aim of transferring it to Brazilian industry and the country was close to possessing an industry based on titanium and reactive metals. Titanium received huge investment from Brazil's federal government (Henriques, 2008). For Brazil, the Titanium Project was important for the following reasons: it provided acquisition of wide experience in the titanium, that culminated in the award of a patent, which received an important Brazilian Prize for innovation techniques in 1980; - Brazil became self-sufficient in titanium sponge production, in a process previously only available in a closed group of industrialized countries; it remains to this day the only successful experience in metallic titanium production in Latin America; it succeeded in placing on the Brazilian market a reasonable amount of Ti sponge (in the main program alone, around 30t was produced in the CTA); it promoted knowledge of the metallic chloride reduction technology and the production of reactive metals, such as zirconium, uranium, niobium and magnesium; and provided the necessary experience in vacuum metallurgy for the manufacture of reactive alloys and metal refining, generating the advance of the Brazilian industry (Henriques, 2008). Historical facts about the Titanium Project 1965 - Studies at the CTA start with the elaboration of the first project backed by the National Bank of Development (BNDE); 1966 - Construction of the pilot-plant infrastructure; November - Signature of the contract with BNDE; 1967 - Start of the assembly of the pilot-plant equipment; 1968 - Inauguration of pilot-plant May - first operation of the TiCl4 purification plant. Accident in the plant, with leaking of titanium tetrachloride from the distillation tank, causing the interruption of the unit; September - operation of the reduction plant; 1969 - May - restart of the TiCl4 purification plant; June V. 1, n. 1, Jan. - Jun. 2009

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second operation of the reduction plant; July - operation of the reduction plant; August - first operation of the vacuum distillation plant; September second operation of the vacuum distillation plant. 1970 - 1972 - integrated operation of pilot-plant in order to introduce modifications to the original equipment aimed at the unification of the reduction and distillation plants; operations on a scale of 100 kg of sponge; 1973 - 1976 Routine operation: - consolidation of the modifications. - Production of 200 kg of sponge; - End of main development works. 1977 - Patent Request to INPI; 1977 - 1978 - Transfer of the Titanium Project to VALEP (subsidiary of Vale do Rio Doce Company, CVRD); 1979 - Interruption of the negotiations; 1980 Negotiations with METAMIG; 1981 - Signature of agreement number: 02-IPD/81, between CTA and METAMIG; 1982 - Implementation of first work program with METAMIG; 1983 - 1985 - Interruption of the works due to financial problems with METAMIG; Negotiations with CVRD for the transfer of agreement number: 02- IPD/81; 1986 - Signature of the Additive Term number: 06-IPD/86, transferring agreement CTA/METAMIG to CVRD - Start of the work program with CVRD; 1987 - Finish of the work program with CVRD. End of titanium sponge production at the CTA. Summary of the Titanium Project All the goals of the agreement with CVRD were reached (Rover, 1971a, Rover, 2005): evaluation of the equipment behavior; training of a new operation team (CVRD); evaluation of the product quality; and the investigation of the necessary parameters for the construction of the titanium production plant. The original reactor was patented in a simpler and more efficient version, increasing production capacity, from 450 to 750 kg of sponge per operation, in the same time (72 hours) (Rover, 1971b). Out of 30 operations as agreed with CVRD, 29 were effectively carried out, with consumption of around 64 tons of titanium tetrachloride, imported for the program. The pilot plant was operated in the condition of one operation a week, during 10 months of intensive training with the CTA team. At the end of the program, the CVRD team carried out the six last operations, without problems, having been Journal of Aerospace Technology and Management

judged ready to use the technology (Rover, 2005). The quality of the sponge produced in the AMR pilot plant was well within international norms. The Titanium Project ended in 1987. The titanium sponge blocks were broken up at the AMR (300t press) and the final milling was carried out at CVRD which commercialized part of the product. The Titanium Project evaluated normally with the total transfer of the technology developed in the CTA to a Brazilian company. This transfer was made with the complete participation of the CVRD technicians who were incorporated into the AMR teams and remained at the AMR premises for more than one year, observing and learning all the details of the titanium sponge production (Rover, 1970a, Rover, 1970b). After more than one year of effective work, in a period of 20 years, the CTA transferred all the developed technology to CRVD, hoping that the patented process would be industrialized and it provided the necessary support for new research. In an additional gesture to facilitate the implantation of the titanium industry in Brazil, CTA transferred to CVRD all the equipment from its pilot plant. CVRD operated the pilot plant in Santa Luzia, Belo Horizonte, from June, 1988, having produced about 30t of titanium sponge. Financial difficulties and the reorientation of CVRD goals and objectives led its technology managers to suspend the plant operations in 1991. In 1994, CVRD returned the equipment that was brought back to AMR's warehouse (Henriques, 2008). Process of titanium sponge production The titanium sponge production in the AMR pilot plant was carried out using the Kroll process, which consists of TiCl4 reduction by magnesium, in accordance with the following chemical reaction: TiCl4 + 2Mg

Ti + 2MgCl2.

This operation was processed in a “reactor-retort”, socalled since the reduction and distillation operations were carried out in the same container as shown in Fig. 2 (Rover, 1970b). A magnesium load (bars of 9 kg) should be heated to 750°C, for the titanium tetrachloride injection. The entire reaction is developed in an inert atmosphere (argon), due to the high titanium reactivity with atmospheric gases, preventing the final product contamination. In addition to titanium sponge, a large amount of MgCl2 is formed as sub-product, that is poured out during the operation, leaving at the end, a sponge with Mg and MgCl2 residual contents (Rover, 1971b). The vacuum distillation stage is initiated with the action of the high vacuum system at 950C. Metallic magnesium and magnesium chloride vapors (used in excess in the reduction), are collected in the condenser. The operation lasts around 30 hours, depending on the amount of distilled material. The reactor is removed from the furnace, until it V. 1, n. 1, Jan. - Jun. 2009

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reaches room temperature. The cartridge is removed for cleaning, prior to a new reduction stage (Rover, 1971b).

Titanium Ingot manufacturing After the reduction and distillation stages, a final purification of the sponge is necessary using vacuum arc furnaces in order to eliminate residual impurities and to manufacture the ingots (Fig. 4).

Figure 4: Titanium ingot manufacturing at CTA's plant (Henriques, 2008). Manufacture of electrodes

Figure 2: Reactor-retort, equipment developed by CTA for titanium sponge production (Henriques, 2008).

The sponge is removed from the cartridge in a compact block of about 750 kg and stored for future breaking and melting as consumable electrode in vacuum. In industry's case, all the magnesium chloride obtained (from the reduction or distillation stages) would be recycled by means of electrolytic cells, returning to the system as chlorine and magnesium. The yield is around 70 per cent for chlorine and 90 per cent for magnesium. The chlorine would be sent in gaseous state to the chlorine plant and magnesium (liquid), taken directly to the reduction installation (Rover, 1973). Figure 3 shows the stages of the Kroll process used at CTA's plant [21].

Figure 3: Stages of titanium sponge production (based on the Kroll process) used at the CTA plant (Henriques, 2008). Journal of Aerospace Technology and Management

The technique for manufacturing consumable electrodes from the titanium sponge includes compaction of sponge particles (15mm) and posterior welding of the compacts. A hydraulic press (100t) was used in the pressing stage, aimed at the production of ingots of 200mm in diameter (Faria, 1990). The pressing was carried out in a cylindrical die, with 52mm of internal diameter, without lubrication. The second stage consists of welding the compacts by means of resistance heating, in sufficient numbers to obtain the electrode. During the heating, the compacts are kept under stress. With this process, in addition to welding, an increase in the mechanical resistance of the compacts is obtained by sintering (Faria, 1990). Melting and remelting of the consumable electrodes The process commonly used in titanium ingot manufacture is vacuum arc melting with consumable electrode. This process uses the thermal energy of an arc as heat source. Due to the intense heat generated in the arc, a uniform â&#x20AC;&#x153;sprayâ&#x20AC;? flow is established from the melting electrode, that accumulates in the ingot-mold, forming a casting metal pool that solidifies rapidly (Henriques, 2008). The maintenance of a stable arc and a constant distance between the electrode and the casting metal is important for the metallurgic quality of the ingot (Faria, 1990). The flatter the pool, the less tendency for solute segregation or undesirable phase concentration. Factors affecting the mass transfer inside the pool due to thermal convection and interaction with the magnetic fields are also important. After the assembly of the electrode, start material (titanium chips) is deposited in the bottom of the ingot-mold, as a protective base. The chamber is closed and evacuated up to a pressure -1 of 1,333x10 Pa. With the establishment of an arc between the electrode and the start material, the melting begins. V. 1, n. 1, Jan. - Jun. 2009

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Direct polarity is used; the electrode is negative, where 2/3 of the power will concentrate in the metal pool (Henriques, 2008). Voltage gradients are relatively low, in the order of 20 to 50V, depending on some factors, including gas content in the furnace and the electrode, the required current, length of the arc, resistance of the electrode and ingot size (Henriques, 2008). Once the arc is initiated, the current is increased slowly to the desired level. This current will determine the melting rate, depth of the metal pool and surface quality of the ingot. Before the electrode melting is completed, the current is reduced gradually to allow the solidification of the metal pool to occur without the development of deleterious defects. After ingot cooling, the chamber is aired and a new electrode is fixed to the connecting rod and centered (Faria, 1990). On top of the first casting deposited in the ingot-mold, titanium chips must be placed, and, again, the chamber must be closed, vacuumed, repeating the entire procedure for the melting of the first electrode. The successive melting of about three electrodes is necessary to form a first melting ingot. The ingot, after final cooling, is removed from the ingot-mold and all the procedures are repeated for production of the next ingot, and so on repeatedly, until sufficient ingots are obtained to form an electrode for remelting. The ends of the first melting ingots must be cut, top and bottom, and the surfaces must be smoothed for welding and remelting, after the ingot-mold removal. A remelting is considered necessary for all the applications to ensure an acceptable degree of homogeneity in the ingot (Faria, 1990). For a second remelting ingot production, it is necessary to weld the ingots face to face, to form an electrode of compatible size with the furnace dimensions and the desired final ingot. The welding of ingots is carried out in the melting furnace and after that, adequately centralized. The procedures for the melting of this new electrode are the same as for the ingots obtained from compacted sponge. Figure 5 presents a titanium sponge (750kg) and titanium ingot (260kg) produced at CTA during the 80s (Faria, 1990). Powder metallurgy With the completion of the Titanium Project at CTA, the Materials Division (AMR) began the development of powder metallurgy (P/M) techniques aimed at titanium alloy production, mainly because of the low production costs and the operation facilities. Powder metallurgy is now a mature commercial metalforming technology with the intrinsic advantage of net or near-net shape capability. P/M techniques afford designers the ability to produce significantly complex near-net shape parts at a potentially significant cost saving, with low material loss and it has been applied at CTA since 1998. Unfortunately, the parts are limited in size and complexity, as well as being less than 100 per cent of theoretical density, which can adversely affect mechanical properties (Henriques, 1999, Henriques, 2001). Journal of Aerospace Technology and Management

Figure 5: Titanium sponge (750kg) and titanium ingot (260kg) produced in CTA (Henriques, 2008). Two methods are used to produce titanium powder from titanium ingots: hydride/dehydride and molten metal fragmentation. In the hydride/dehydride process, the ingot is exposed to hydrogen under conditions in which it forms a brittle titanium hydride. The brittle hydride is crushed to the required powder size, and then the conditions are altered to remove the hydrogen, thus producing titanium powder. In the molten metal fragmentation process, the titanium is melted and fragmented, either by centrifugal force on the rim of a spinning titanium disk, or by gas jet disruption of a molten titanium stream (Henriques, 2003a, Henriques 2003b). As with the process to produce titanium ingot, the processes required for titanium powder are also complex and inherently expensive. This forces the prices to be rather high and results in a very small market for titanium powder. A less expensive way is the use of titanium hydride powders (TiH) that can promote high final densification. Titanium P/M preparation At CTA, the process chosen for the preparation of the alloys includes the blended elemental method, using titanium hydrides followed by a sequence of uniaxial and cold isostatic pressings with subsequent densification by sintering. In this review, results of Ti-6Al-4V and Ti-13Nb13Zr sintering are presented (Henriques, 2005, Henriques 2003c). Titanium hydride powders are obtained by the HDH technique from Ti sponge fines. Hydriding is carried out at 500째C in a vertical furnace for 3 hours under a positive V. 1, n. 1, Jan. - Jun. 2009

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pressure. After cooling to room temperature, the friable hydride is milled in a niobium container under vacuum. Vanadium, niobium, tantalum, zirconium and other reactive metal powders for Ti alloy preparation are obtained using the same route, however with, significantly higher hydriding temperatures ( 800°C). Table 1 shows the principal characteristics of the powders used in Ti-6Al-4V samples. Table 1: Characteristics of the powders used in the Ti-6Al-4V preparation (Henriques, 2005).

Figure 6: Plot of density vs. sintering temperature for Ti-6Al-4V. Dotted line indicates the theoretical density of the alloy (Henriques, 2005).

Microstructural development The starting powders are weighed and blended for 15 minutes in a double-cone mixer. After blending, the powders are cold uniaxially pressed at a pressure of 80 MPa, in cylindrical 20mm diameter dies. Afterwards, samples are encapsulated under vacuum in flexible rubber molds and cold isostatically pressed (CIP) at 350 MPa for 30 seconds in an isostatic press (Henriques, 2005). Sintering and microstructural characterization

Samples of Ti alloys present high densification, varying between 69 and 71 per cent of the theoretical specific mass after cold isostatic pressing, and between 93 and 95 per cent, after sintering, with homogeneous microstructure. Most of the titanium alloys presented a Widmanstätten-like microstructure, two-phase (), with low porosity. The amount of the Widmanstätten microstructure increased with the sintering temperature. The hardness values are a function of the sintering temperature, lying in the range from 370 to 400 HV for the specimens prepared at 1500°C.

Sintering is carried out in a titanium or niobium crucible in high vacuum condition (10-7 Torr). Sintering temperatures ranged between 900 and 1500°C and heating rates of 20°C/min. After reaching the nominal temperature, samples are held at the chosen temperature for 1 to 2 hours and then furnace cooled to room temperature. Metallographic preparation is carried out using conventional techniques. Specimens are etched with a Kroll solution: (3mL HF: 6mL HNO3: 100 mL H2O) to reveal their microstructure. Microhardness measurements are carried out with load of 0.2 kgf. Photomicrographs are obtained using a scanning electronic microscope. The density of the sintered samples is determined by the Archimedes method (Henriques, 2003).

A typical issue related to the flow of hydrided powders is observed in the microstructural evolution. Hydrided powders present an angular and irregular morphology. With the enlargement of the surface area, the friction level in powder mass increases. Consequently, the friction between particles is high, providing low flow and packing rates. Figure 7 presents areas with agglomerations of niobium particles that occur due to the low powder flow, preventing a good homogenization between the elemental hydrided particles, which require high sintering temperatures to achieve the total dissolution of these agglomerates and complete homogenization of the alloy (Henriques, 2008).

The influence of sintering temperature on the densification of the Ti-6Al-4V alloy was studied using isochronal sintering (holding time of 1h). Results are shown in Fig. 6. Density varies very little between 700 and 900C. Densification is speeded up between 900 and 1000C, the expected range for transus- with accompanying increase in diffusivity, reaching a maximum value of about 99.8 per cent of theoretical density at 1500C (Henriques, 2005).

An important fact in the microstructural development of titanium alloys produced by P/M is the dependence on the dissolution of metal particles with high melting points (normally β-stabilizers as Nb, V, Zr, Ta). Therefore, the microstructural development is only completed after the total dissolution of these elements in the titanium matrix which yields to a homogenous microstructure, as shown in Fig. 8 (Henriques, 2005).

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1300 C Figure 7: Microstructure of Ti-13Nb-13Zr sample sintered at 1100 째C presenting areas with niobium agglomerations (Henriques, 2008).

It can be observed that the Widmanst채tten-like structure (basket weaved) grows with the dissolution of the stabilizing particles through the increase in the sintering temperature. The dissolution of vanadium particles is very fast and at 1300C there are few regions without a two-phase microstructure. At the higher sintering temperature (/1500C), individual vanadium particles are found completely dissolved. Concerning the Widmanst채tten microstructure, the dark-contrasting areas are -phase plates. The -phase, present among -plates, gives rise to a white contrast (Henriques, 2005).

1500 C Figure 8: Microstructural development of Ti-6Al-4V alloy showing the Widmanst채tten growing from vanadium dissolution between 900 - 1500C (Henriques, 2005).

The expansion/contraction behavior during titanium alloy sintering brings important information in order to obtain high levels of densification. The sintering of Ti-13Nb-13Zr compacts using hydrided and dehydrided powders was investigated using a dilatometer (Henriques, 2008). The results are shown in Fig. 9.

900 C

Figure 9: Expansion/contraction behavior in Ti-13Nb-13Zr sample sintered up to 1500C (Henriques, 2008).

1100 C Journal of Aerospace Technology and Management

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powders, the compacts expand slightly with the temperature increase. At 800C, contraction owing to densification starts. This temperature is close to the transus temperature of titanium powders. Since the diffusivity of titanium is much higher than that of titanium, it is speculated that mutual diffusion between titanium and the other elemental powders is activated through the range of temperatures at which titanium is phase. Densification continued up to 1200°C and overall contraction exceeding 6 per cent was achieved. In the Ti13Nb-13Zr sample produced with hydrided powders, after a slight expansion, the start of contraction is observed between 400-500ºC, close to the dehydriding temperature, which demonstrates the efficiency of the use of hydride powders in relation the dehydrided ones, mainly, in the velocity of the sintering mechanisms, that occur at lower temperatures, probably driven by the atomic movement caused by the diffusion of hydrogen and consequent generation of vacancies, that possess a basic importance in the mechanisms of mass transport and contraction during the sintering of parts produced by powder metallurgy (Henriques, 2001). Densification continued up to 1200C and overall contraction exceeding 11 per cent was achieved (Henriques, 2008). This fact indicates the influence of hydrogen atoms in the sintering mechanisms providing a contraction even at low temperatures (Taddei, 2005, Taddei, 2004). From these results, it was established that the route using blended elemental technique with hydrided powders is the most suitable for aerospace parts production, mainly because of the high densification reached. CONCLUSIONS Future titanium technology development efforts should be directed toward lower final components costs for the aircraft manufacturer. Increased emphasis on delivery cost will make it more difficult for titanium to maintain its share of the structural weight of aerospace systems unless the cost of the components can be reduced. There are two possible approaches, development of lower cost alloys and optimization of the processes in order to reduce the production costs. More and more, engineers are coming to realize the benefits of titanium. This trend will continue and be enhanced through user education. Potential consumers need to be made aware of its outstanding properties, emerging lower cost processes, and its potential benefits to the life cycle of new applications. ACKNOWLEDGEMENT The author would like to thank Major Carlos Firmo Schmidt Rover for his dedication in the development of a Journal of Aerospace Technology and Management

Brazilian technology for titanium production. REFERENCES Allen, P., 1996, “Titanium Alloy Development”, Advanced Materials & Processes, Vol. 10, pp. 35-37. Andersen, P. J., Alber, N. E.; Thellmann, E. L., 1980, “P/M Titanium Reduces Aerospace Components Costs”, Precision Metals, Vol. 104, p. 34-41, Barksdale, J. 1966, “Titanium”, Ronald Press Company, USA. Boyer, R. R., 1994, “Aerospace Applications of Beta Titanium Alloys”, Journal of Metals, Vol. 46, pp. 20-23. Collings, E. W. 1983, “The Physical Metallurgy of Titanium Alloys”, American Society for Metals, USA. Donachie, M. J., 1988, “Titanium: a Technical Guide”, ASM Metals Park, USA, 512. Faria, J., 1990, “Fabricação de Lingotes de Titânio pelo Processo de Fusão a Arco sob Vácuo com Eletrodo Consumível”, Metalurgia-ABM, Vol. 46, No. 392, pp. 530536. Froes, F. H., Eylon, D., 1980, “Developments in Titanium Powder Metallurgy”, Journal of Metals, Vol. 32, pp. 47-54. Froes, F. H., 1998, “The Production of Low-Cost Titanium Powders”, Journal of Metals, Vol. 9, pp. 41. Froes, F. H., 2004, “How to Market Titanium: Lower the Cost”, Journal of Metals, Vol. 56, No. 1, pp. 39. Hanson, B. H., 1995, “The Selection and Use of Titanium”, Institute of Materials, USA. Henriques, V. A. R, Bellinati, C. E., Silva, C. R. M, Moura Neto, C., 1999, “Desenvolvimento da Metalurgia do Pó (M/P) em Titânio na Indústria Aeronáutica”. SAE Technical Papers Series, No. 1999-01-3013, pp. 1-5, Henriques, V. A. R, Bellinati, C. E., Silva, C. R. M., 2001, “Production of Ti-6% Al-7% Nb Alloy by Powder Metallurgy (P/M)”. Journal of Materials Processing Technology, Vol. 118, pp. 212-215. Henriques, V. A. R; Sandim, H. R. Z.; Silva, C. R. M., 2003, “Dissolution of Niobium Particles During Ti-6Al-7Nb Sintering”, Materials Science Forum, Vol. 416-18, pp. 257262. Henriques, V. A. R, Sandim, H. R. Z., Coelho, G. C., Silva, C.R.M., 2003, “Microstructural Evolution During Hot Pressing of the Blended Elemental Ti-6% Al-7% Nb Alloy” Materials Science And Engineering A, Vol. 347, pp. 315324. V. 1, n. 1, Jan. - Jun. 2009

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Henriques, V. A. R, Moura Neto, C., 2005, “Sintering of Titanium Alloys for Advanced Aerospace Systems”, SAE Technical Papers Series, No. 2005-01-2813, pp. 1-5. Henriques, V. A. R, Silva, C. R. M; Bressiani, J. C., 2003, “Utilização de Técnicas de Metalurgia do Pó (M/P) na Obtenção da Liga Ti-13Nb-13Zr”, M & M Metalurgia e Materiais, Vol. 59, No. 532, pp. 7-10. Henriques, V. A .R, Sandim, H. R. Z; Silva, C. R. M., 2003, “Use of Titanium Powders Obtained by The Sponge Screening and for The HDH Process in The Titanium alloys Production for Powder Metallurgy (P/M)”, Materials Science Forum, Vol. 416-18, pp. 23-28. Henriques, V. A. R, Silva, C. R. M., 2001, “Production of Titanium Alloys for Medical Implants by Powder Metallurgy”, Key Engineering Materials, Vol. 189, pp. 443448. Henriques, V. A. R.; Cairo, C. A. A.; Silva, C. R. M., Bressiani, J. C., 2005, “Production of Titanium Alloys for Advanced Aerospace Systems by Powder Metallurgy”, Materials Research, Vol. 8, No. 4, pp. 443-446. Henriques, V. A. R., 2008, “Titânio no Brasil”, Associação Brasileira de Metalurgia e Materiais, 373p, Brazil. Hurless, B. E, Froes, F. H., 2002, “Lowering the Cost of Titanium”, The AMPTIAC Quarterly, Vol. 6, No. 2, pp. 3-9. Kroll, W. J., 1937, Z. Anorganische Chemie, Vol. 234, pp. 422.

Rover, C. F. S., Ferrante, M., Santos, P. R. G. 1970b, “A Redução do TiCl4 pelo Mg na Obtenção da Esponja de Ti na Usina-Piloto do CTA”, Proceedings of the XXV ABM Congress; Porto Alegre, Brazil, pp.27-31. Rover, C. F. S., Ferrante, M., Santos, P. R. G., 1971b, “Novo Equipamento de Redução e Destilação a Vácuo na Produção de Esponja de Titânio”, Proceedings of the XXVI ABM Congress; Rio de Janeiro; Brazil, pp. 905-911. Rover, C. F. S., Ferrante, M., Santos, P. R. G. 1973, “Adição Simultânea de Mg e TiC14 na Produção de Esponja de Titânio”, Proceedings of the XXVIII ABM Congress; Salvador, Brazil, pp.43-49. Stephen, S. J., Froes, F. H., 1988, “Titanium Metallurgy and Applications”, Light Metal Age, Vol 46, No. 11, pp. 5-12. Seong, S. 2009, “Titanium: Industrial Base, Price Trends, and Technology Initiatives”, Rand Corporation, 154p, USA. Taddei, E. B., Henriques, V. A. R., Silva, C. R. M., Cairo, C. A. A., 2005, “Characterization of Ti-35Nb-7Zr-5Ta Alloy Produced by Powder Metallurgy”, Materials Science Forum, Vol. 498-499, pp. 34-39. Taddei, E. B., Henriques, V. A. R, Silva, C. R. M, Cairo, C. A. A., 2004, “Production of New Titanium Alloy for Orthopedic Implants”, Materials Science & Engineering. C, Biomimetic Materials, Sensors and Systems, Vol. 24, No. 5, pp. 683-687.

Kroll, W. J., 1940, Trans. Electrochem. Soc., Vol. 78, pp. 35. Leyens C., Peters M., 2003, “Titanium and Titanium Alloys: Fundamentals and Applications”, John Wiley & Sons, 260p, USA. Lütjering G., 2007, “Titanium (Engineering Materials and Processes)”, Springer, 300p, USA. Rossman, E., 2007, “Straightening of Titanium Alloy Parts”, Industrial Press, pp. 80, USA. Roza, G. , 2008, “Titanium”, Rosen Central, pp. 48, USA. Rover, C. F. S., Santos, P. R. G., Ferrante M., 1971a, “A Redução do TiCl4 pelo Mg na Obtenção de Esponja de Titânio na Usina Piloto do CTA”, Metalurgia”, Vol. 27, No. 158, pp. 11-18. Rover, C. F. S., Henriques, V. A. R., Cairo, C. A. A., Moura Neto, C., 2005, “Titânio no Brasil”, Metalurgia e Materiais, São Paulo, Vol. 61, No. 559, pp. 519-521. Rover, C. F. S., Ferrante, M., Santos, P. R. G., 1970a, “A Purificação do Tetracloreto de Titânio na Usina-Piloto do CTA”, Proceedings of the XXV ABM Congress; Porto Alegre, Brazil, pp. 32-41. Journal of Aerospace Technology and Management

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João Batista P. Falcão Filho* Institute of Aeronautics and Space São José dos Campos - Brazil jb.falcao@ig.com.br

Ana Cristina Avelar Institute of Aeronautics and Space São José dos Campos - Brazil anacristina@iae.cta.br

Maria Luísa C.da C. Reis Institute of Aeronautics and Space São José dos Campos - Brazil mluisareis@iae.cta.br

*author for correspondence

Historical review and future perspectives for Pilot Transonic Wind Tunnel of IAE Abstract: The Pilot Transonic Wind Tunnel of Institute of Aeronautics and Space (PTT Pilot Transonic Wind Tunnel) is an important result of a tremendous effort to install a high speed wind tunnel complex (TTS acronyms for Transonic and Supersonic Tunnels, in Portuguese) at the IAE, to support Brazilian aerospace research. Its history is described below, starting from the moment the TTS project was first conceived, highlighting each successive phase, mentioning the main difficulties encountered, and the solutions chosen, up until the final installation of the Pilot facility. A brief description of the tunnel's shakedown and calibration phases is also given, together with the present campaigns and proposed activities for the near future. Key words: Aerodynamics, Calibration phase, Experimental tests, Pilot installation, Transonic wind tunnel.

LIST OF ABBREVIATIONS AEB ALA AEDC ARA BAe CFD CNPq

Brazilian Space Agency Aerodynamics Division of the IAE Arnold Engineering Development Center (USA) Aircraft Research Association Ltd. (England) British Aerospace (England) Computational Fluid Dynamics National Council for Scientific and Technological Development (Brazil) CTA General-Command of Aerospace Technology DFVLR Deutsche Forschungs-Und Versuchsanstalt für Luft-Und Raumfahrt e. V. (Germany) DLR Deutsches Zentrum für Luft- und Raumfahrt (Germany) EEI Industrial Engineering College (São José dos Campos) FINEP Brazilian National Agency for the Financing of Project and Studies (Brazil) GTTS Work group for the installation of transonic and supersonic wind tunnels facility in Brazil IAE Institute of Aeronautics and Space (of the CTA) JAXA Japan Aerospace Exploration Agency ONERA Office National D'Etudes et Recherches Aeroespatiales NAL National Aerospace Laboratory (Japan) NASA National Aeronautics and Space Administration NLR National Lucht-En Ruimtevaartlaboratorium (Netherlands) PSP Pressure Sensitive Paint PTT Pilot Transonic Wind Tunnel (at the Aerodynamics Division of the IAE) ____________________________________ Received: 05/05/09 Accepted: 12/05/09 Journal of Aerospace Technology and Management

TA-2

Brazilian Subsonic Industrial Wind Tunnel at the Aerodynamics Division of the IAE TsAGI Central Aero-Hydrodynamic Institute (Russia) TTS Transonic and Supersonic Wind Tunnels (Brazil) UNITAU University of Taubaté UNIVAP University of Vale do Paraíba USP University of São Paulo INTRODUCTION The Pilot Transonic Wind Tunnel of Institute of Aeronautics and Space (PTT - Pilot Transonic Wind Tunnel) originated from the TTS-Project (Complex of Transonic and Supersonic Wind Tunnels). The TTS-Project was created in the mid-eighties with the aim of building a high speed aeronautical complex of wind tunnels, as a suitable tool for the Brazilian aeronautical industry. This effort would allow aerodynamic tests in the high speed range (up to Mach number 4), reaching strategic goals of safety and up-to-date testing for new Brazilian aerospace projects for the Air Defense. At that time, the only industrial wind tunnel was the subsonic TA-2, with a test section of dimensions 2 m 3 m. The first step was carried out in 1985, with the creation of a work group to study the problem. The first task was to contact potential national users through technical meetings to draw up an extensive report to fully support the idea for the next phases of the project. Embraer, Avibrás, D. F. Vasconcelos, and Engesa companies; and the IAE/CTA research institute were contacted at that time (David et al., 1985). After processing the collected information, a first technical specification for V. 1, n. 1, Jan. - Jun. 2009

Falc達o Filho, J. B. P., Avelar, A. C., Reis, M. L. C. C.

two industrial facilities was undertaken: one continuously driven transonic wind tunnel (test section of 2 m x 2.4 m and Mach number from 1.2 to 1.4); and another intermittent supersonic blowdown wind tunnel (test section of 1.2 m x 1.2 m and Mach number from 1.2 to 4.0). Embraer appeared as the main client for both wind tunnels, with about 52 per cent of the occupation time (GTTS, 1986, Escosteguy, 1987). The first conception of the tunnels was at that time a very modern installation including some technological challenges. Some important references in transonic tests were consulted during the initial specifications (Davis et al., 1986, Wu and Moulden, 1976, Goethert, 1961, Reed et al., 1977, Pope and Goin, 1978, Steinle and Stanewsky, 1982, Eckert et al., 1976). The transonic wind tunnel would be continuously driven not only by a main compressor but also by an injection system, which would help to enlarge the operational tunnel envelope, without penalizing the installed power. Because of this new feature, a pilot transonic wind tunnel was conceived in order to test this challenging new idea, and a special concern was raised about the optimization of running conditions by setting the automatic system parameters in a combined action of the main compressor and the intermittent injection system. This tunnel is a 1/8th scale down of the planned industrial transonic facility, completely representative of its functions and subsystems. With the specifications defined, the work group sought a specialist company as a partner for the project. Figure 1 shows the operational envelopes of the wind tunnel facilities (present subsonic TA-2, planned transonic and supersonic wind tunnels, and the Pilot Transonic Tunnel).

Figure 1: Operational envelopes of the wind tunnels in the planned facilities of CTA - Reynolds number is based on typical chord.

After completion of the technical and commercial analysis the Sverdrup company was chosen. During two technical visits (one to Europe and another to the USA) the GTTS work group contacted ONERA, DFVLR, NLR, BAe, ARA in Europe (Nogueira and Passos, 1986a), and FluiDyne, Calspan and Sverdrup, in USA (Nogueira and Passos, 1986b). The work group spent a 6-month period at Sverdrup Technology Inc., which was responsible for the Journal of Aerospace Technology and Management

development of the conceptual design of the industrial transonic facility (Sverdrup, 1987a) and of the detailed design for a scaled down 1/8th pilot transonic facility (Sverdrup, 1987b). For several reasons, mostly related to budget restrictions, only the pilot facility design was completely built. Table 1 summarizes the main events during the TTS Project and shows perspectives for the near future under the present test campaigns. In order to emphasize the importance of government participation in this kind of effort, it should be mentioned that, a wind tunnel project has a typical investment return of around 20 years, which generally makes them not very attractive to private companies, although these are also potential users. Therefore, wind tunnel projects are naturally considered a government issue. Moreover, it is considered a government issue also because it should be a political and strategic decision to invest in the technological strengthening of the nation's Aerospace power. It is also worthwhile to set forth the pioneering work done by the GTTS team in creating the possibility of a high speed aerodynamic test facility in Brazil, which today possesses only one subsonic industrial installation, while other countries with lesser aeronautical traditions, such as South Africa, Indonesia, Holland, China and Iran, have their own. Some important issues were assessed during the TTS project development, and they are worth noting. For example, the installation site definition. Considering criteria of the proximity of existing tunnel installations (subsonic tunnel TA-2), the availability of shared resources (technical team, computing, electricity, model shop etc.), the proximity of potential clients, allowing quick exchanges of people and materials, the availability of electricity and water (as obtained from the suppliers at that time), the installation of the TTS close to the lake in IAE, near the TA-2 subsonic tunnel facility, was a common sense solution among other possible sites considered. Figure 2 shows the selected site for the TTS project. Other important aspects were also considered, such as potential for future expansions, the environmental impact (cutting of trees, noise, chemically treated water leakage impact, etc.), interference in non-industrial areas, easy access, access to high voltage electric cables, easy access for employees, site preparation, installation of security and costs. After that, the chosen site was thoroughly investigated, and land sounding was performed, annual temperature and wind cycles, water availability and physical-chemical properties were determined, a study of the renewable water source from the lake was considered and availability of electrical energy was investigated by the source supplier. To perform these studies, the TTS technical team consulted competent sectors, such as INPE, Eletropaulo, Sverdrup Technology Inc., and other CTA divisions and institutes. V. 1, n. 1, Jan. - Jun. 2009

Historical review and future perspectives for the Pilot Transonic Wind Tunnel of IAE

Table 1: Main events during TTS Project. Year

Events

1985

! Creation of the TTS technical team; ! Contact with potential users (technical report made); ! Technical specification definition for two industrial wind

1986

Special computing programs were developed to calculate the noise distribution in the nearby area based on the noise source data provided by Sverdrup Technology Inc., and to evaluate the impact of a high pressure air reservoir burst. All this information is documented in the TTS project (GTTS, 2009) and presenting the results here would be too long.

tunnels (one transonic and one supersonic);

19861987

! Possible installation site analysis and definition, based on natural and available resources;

! Graphic conception to comply with operation and security requirements;

! Research for international and national expertise in wind tunnel design and industrial support;

! Research for environmental data and land characteristics to support the idea of installation nearby the TA-2 site;

! Conceptual design of the TTS wind tunnel complex with 19881989

the help of Sverdrup Technology Inc. (USA);

! Restriction from US DoD to the Supersonic Project; ! Brazilian government economic restrictions led to the Pilot Transonic Tunnel design;

! Conceptual design of PTT, and definition of systems and components, by Sverdrup Technology Inc. (USA);

! Search for financial resources from Air Ministry, DIRENG 19901992

and FINEP research funding organization to proceed with the Industrial Transonic Facility;

! Technical studies of Pilot Transonic Tunnel aerodynamic circuit;

! Detailed design of the Pilot Transonic Tunnel with open 19931995

aerodynamic circuit, driven only by injection system;

! Construction and Installation of the Open Circuit Pilot Transonic Tunnel at ITA;

! Use of US$ 3 million (90% from Air Ministry, 10% from 19961997

FINEP) in the complete aerodynamic circuit design and construction of the pilot facility;

! Installation of the Pilot Transonic Tunnel at ALA; ! Search for alternatives for a low cost Industrial Transonic Facility at TsAGI (Russia);

19981999

20002001

! Search for resources to start-up TTP main components (inverter, motors, compressors), circuit alignment and systems integration main program;

! Aerodynamic circuit alignment; ! Start-up of main power group and other tunnel components;

! Automatic control systems integration and main control program based on LabView platform;

20022004

2004

! Data control and acquisition equipment installation; ! Tests for automatic control systems adjustments; ! Systems integration tests; ! Pilot Transonic Tunnel Calibration tests; ! Damage caused by an atmospheric electric discharge on the main inverter;

! Search for financial resources and from FINEP to fix the 20052006

main inverter;

! Calibration tests performed using injection system with open aerodynamic circuit;

! Resources approved by FINEP to fix and modernize the control systems for the PTT;

! Development of project from VLS 20072010

Associated Technologies (AEB) to obtain know-how in sounding vehicles technology, by performing tests with VS-30;

! Development of project from VLS

Associated Technologies (AEB) to obtain know-how in PressureSensitive-Paint (PSP) in sounding vehicles testing, by performing tests with VS-40

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Figure 2: Proposed TTS installation site.

The project has inspired many theoretical studies to clarify specific technical aspects of the wind tunnel, among them, Master Degree thesis (Falcão Filho, 1996) and Doctoral Degrees dissertations (Fico Jr., 1991; Falcão Filho, 2006), besides many other scientific reports (Nogueira et al., 1988; Nogueira and Falcão Filho, 1998; Ortega and Escosteguy, 1988; Falcão Filho, 1990; Ortega and Fico Jr., 1991; Fico Jr. and Ortega, 1993; Escosteguy and Nogueira, 1997; Vieira et al., 1997a, 1997b; Falcão Filho et al., 1998, 2000a, 2000b, 2000c; Falcão Filho, 2000; Escosteguy, 1998; Falcão Filho and Ortega, 2007a, 2007b, 2008). The TTS project had, in chronological order, the following heads: Flávio de Carvalho Passos (Lieutenant Colonel, 1985-1986), Marcos Luiz Pereira (Colonel, 1986), Sidney Lage Nogueira (Civilian, 1986-1987), Wilson Cavalcanti (Lieutenant Colonel, 1987-1988), Roberto Kessel (Colonel, 1988-1990), Sidney Lage Nogueira (Civilian, 1990-1997), and João Pedro Caminha Escosteguy (Civilian, 1997). The original TTS project for building industrial facilities for high speed tests was practically interrupted in 1997, when the PTT was still under construction. At that time, the GTTS technical team prepared a report considering some of the possible options to be adopted in order to attain the original goal of having a high speed aerodynamic tests capability in Brazil. Part of the work group went to Russia (in TsAGI) for 10 months, sponsored by the CNPq agency, for a scientific expertise analysis of the original conceptual design for a lower cost transonic wind tunnel design as an alternative solution (Neiland, 1997). Table 2 shows the four possible situations set forth at that time, which are still under consideration by our authorities. The estimated cost values in Table 2 refer to the present time, taking into account monetary inflation over this period. V. 1, n. 1, Jan. - Jun. 2009

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Table 2: Four alternatives for the TTS project continuation. Costs in millions of US$ and the electric power installed in MW. Description

US$ millions

Original conception

Revision based on the Russian proposal made in 1997

Development of a blowdown trisonic project

Acquisition of an existing blow-down trisonic facility

150

MW Advantages

Disadvantages

Very modern and versatile installations

Expensive; Long period until fully operational (8 years)

Cost reduction

Limited productivity; Long period until fully operational (6 years)

Considerable cost reduction

Limited tests capabilities and productivity;

Short period to become fully operational (2 years)

Limited test capabilities and productivity; Eventual technical problems to be detected

110

All subsystem automatic controls use National Instruments data transfer cards with LabView computer interface. Technical details regarding PTT can be found in Falc達o Filho and Mello (2002).

Under the new idea of having only the pilot transonic tunnel, the GTTS work group extended the original conception to obtain a more versatile facility. So, the tunnel would be useful not only to test the new technological challenges for the industrial facility, such as the combined operation with the injection system, but also to perform all kinds of academic tests and tests with simple configuration models.

The tunnel is a 1/8th scale down from the industrial transonic project, and it was initially designed to study the innovative features of the industrial facility, specifically concerned with the injection system operation in combination with the conventional main compressor operation. It was also designed for training the technical team in high speed tests, to perform basic research and academic research assessment, to produce tests in developing new aerodynamic transonic profiles, tests with simple geometry vehicles, qualitative tests of airplane basic configuration, anemometric tests, and others. To accomplish this, the tunnel has three sets of six multi-component internal balances manufactured by MicroCraft for measuring forces and moments, two modules of 16 pressure channels PSI (Pressure Sensitive Instrument) for pressure distribution tests, a Schlieren visualization system, hot-wire equipment, and will have in the near future a PSP (Pressure Sensitive Paint) technique to determine pressure distribution over the model surface. In addition, the tunnel possesses a 2D probe positioning system, angle of attack remotely controlled system and re-entry flap capability. Figure 4 shows a partial view of the aerodynamic circuit of the PTT.

Main Characteristics of the Pilot Transonic Facility The PTT (Pilot Transonic Tunnel) is a modern installation, with a conventional closed circuit, continuously driven by a main compressor of 830 kW of power, and with an intermittent injection system which operates in a combined mode, for at least 30 seconds. Its test section is 30 cm wide and 25 cm high, with slotted walls. The tunnel has automatic pressure controls (from 0.5 bar to 1.25 bar), Mach number (from 0.2 to 1.3), temperature and humidity, in test section. Figure 3 shows its operational envelope.

Figure 3: PTT's operational envelope.

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Figure 4: Partial view of the PTT aerodynamic circuit.

In addition to Sverdrup Technology Inc. (USA), which was responsible for the project design, many other national companies and inner sectors from CTA worked together with the PTT technical team during the design, construction, installation and shakedown tasks of the tunnel project. Among them, IAE (manufacture of many internal parts of the aerodynamic circuit), Embraer (manufacture of some internal parts of the plenum chamber), ABLE (all detailed drawings), INNOBRA (aerodynamic circuit manufacture), M. C. Rocha (tubing installation and aerodynamic circuit alignment), NavCon (integrated control program development), and other components and systems suppliers, ABB (main power generation and control), Martin Bianco (auxiliary compressors and V. 1, n. 1, Jan. - Jun. 2009

Historical review and future perspectives for the Pilot Transonic Wind Tunnel of IAE

dryers), KMS (high pressure air reservoirs), HITTER (control valves), Masoneillan (injection system control valve), ALPINA (cooling tower), ITAIPU (high voltage electrical transformer). Shakedown and Calibration Results From 2002 to 2004, and also more recently, the PTT was subjected to many tests to set subsystem automatic control parameters, installed characteristics and working limits (operational envelope) determination, known as shakedown procedures. The phase where many attempts to assess to all functional characteristics of the tunnel are made over a relatively long period of time is called calibration phase, and it is fundamental in order to guarantee precision levels and productivity, for future tests. During this period of time, all the technical and operational characteristics of the tunnel are documented and used as a reference for future tests. Due to an atmospheric electric discharge which caused the main inverter failure, the calibration phase had to be shortened and limited in many aspects. Some procedures and results will be investigated only in the near future. However, many other significant outcomes have been already obtained, as described in Table 3.

Figure 5: Test section longitudinal Mach number distribution.

Another result is the calibration of internal balances which makes it possible to carry out analysis of aerodynamic loads acting on the model being tested in wind tunnels. A calibration rig was mounted in the PTT area (Fig. 6) and a methodology was developed for the assessment of the uncertainty of the loads supplied by the internal balance. The methodology follows international standardization and it is presented in Reis (2008).

Table 3: PTT Shakedown and calibration reports . Description

Documentation

Preliminary Tests with PTT in Open Circuit Escosteguy, 2000

Falcão Filho and Injection System Behavior in Open Circuit Mello, 2001

Preliminary Calibration Results of PTT

Falcão Filho, 2003

Schlieren System Installation in PTT

Miranda, 2004

Numerical Study of Injection System Operation

Falcão Filho and Ortega, 2007

Longitudinal Mach Number Distribution in Silva and Falcão Test Section (I) Filho, 2007

Reservoirs Polytropic Coefficient Determination

Longitudinal Mach Number Distribution in Zanin et al., 2008a Test Section (II)

10 Multi-Component Internal Balance Calibration 11

Injection System Behavior in Closed Circuit

Goffert and Falcão Filho, 2008

Figure 6: Internal balance calibration rig.

Tagawa et al., 2008 Goffert et al., 2008a

12 Calibration of Flow-meter by insertion turbine

Goffert et al., 2008b

13 Dryer System Analysis

Zanin et al., 2008b

14 Parameters Identification for Injection System

Truyts et al., 2008

15 Calibration Uncertainty Estimation for Internal Balance

Reis et al., 2008

Figure 5 shows one of these results where a Mach number distribution along the nominal test section can be seen. This kind of graphic is used to establish optimum operational conditions at a determined Mach number, by analyzing reentry flaps and plenum chamber forced mass flow extraction effects. Journal of Aerospace Technology and Management

Sounding Vehicles Tests As a transonic wind tunnel, the PTT is a suitable tool to be used to investigate important effects in the transition range. Particularly for IAE sounding vehicles, some physical phenomena can be more precisely assessed and be used for CFD code comparisons. These ideas inspired the proposals for a project, approved for implementation over the period 2007 until 2010, sponsored by the AEB agency through VLS Associated Technology Projects, to perform a complete test campaign with the sounding vehicle Sonda III, named “Realização de Ensaios do VS-30 no Túnel Transônico Piloto do IAE” (Tests Development with VS-30 in the IAE Pilot Wind Tunnel), with financial resources in the order of R$ 300,000.00, with the objective of achieving know-how about sounding vehicles tests. This way, the PTT V. 1, n. 1, Jan. - Jun. 2009

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technical team will be able to help the IAE in its vehicles design research area. Figure 7 shows the Sonda III model installed in the PTT test section to perform forces and moments tests. A new model is currently being prepared with pressure taps in order to analyze pressure distribution on its surface. The experimental data will be compared with CFD results.

Wind Tunnel of ALA for Tests in Sounding Vehicles Models). Resources in the order of R$ 200,000.00 are being used to acquire special equipment (camera, paints, special devices etc.), and for training courses. In the PTT, as with almost all practical aerodynamic testing or basic fluid mechanics experiments, surface pressure measurements are of fundamental importance. Until recently, wind tunnel pressure measurements were performed solely by the use of pressure taps, which need to be connected to transducers. This complicates the model design, it is time-consuming and expensive. In the 1980s the use of the optical measurement method of Pressure Sensitive Paint (PSP) to acquire surface pressure was developed (Denovan et al., 1993, Troyanovsky et al., 1993, Volan and Alati, 1992, Peterson and Fitzgerald, 1980, Kavandi et al., 1990). This method uses a special coating (paint) and digital-imaging technology to obtain surface pressure information at high resolution, and has recently emerged as a powerful tool for global pressure distribution. The fundamental operating principle of PSP is the oxygen quenching of luminescence from the paint.

Figure 7: Sonda III installed in the PTT test section.

To support the new PTT activities, a maintenance Project sponsored by FINEP, “Projeto MCT/FINEP/CT-INFRA PROINFRA 01/2006”, costing around R$ 220,000.00, is presently underway to fix the main inverter unit and modernize the tunnel's automatic control system. To implement these projects, the PTT technical group has welcomed the assistance of many undergraduate students from some outstanding universities (ITA, UNITAU, USPSão Carlos, EEI, UNIVAP) who have participated in academic tasks of scientific initiation (PIBIC-IAE), sponsored by a grant from the CNPq, among other academic activities. Each contribution is either documented by internal reports or reported in conferences (Goffert and Falcão Filho, 2008, Goffert et al., 2008a, 2008b, Zanin et al., 2008a, 2008b, Tagawa et al., 2008). It should be noted that a wind tunnel with these characteristics has an important role in the training of undergraduate and graduate students, since it is ideally suited to performing basic research in aerodynamics.

Light intensity emitted by the paints is measured by a photo-detector, and is inversely proportional to the local air pressure. More details about the PSP principle can be obtained in Liu and Sullivan (2005) and also in the reviews by Bell et al. (2001) and Liu et al. (1997). Conventional paint formulations were first applied to wind tunnel testing in the late 1980s and early 1990s, when the initial tests demonstrated that PSP could successfully resolve the chordwise pressure distribution on a wind tunnel model (Gregory et al., 2008). This method is especially effective for the higher-speed flows (transonic and higher), where the pressure levels and differences are in a much higher percentage of the ambient pressure. The main advantage of the PSP technique is that, in principle, a full spatial distribution of the surface pressures can be obtained, with the spatial accuracy determined by the characteristics of the camera lens and charge-coupled device (CCD). The richness of information that can be extracted from the images permits the investigations of complex flows and comparisons with CFD results. It also offers savings in terms of model instrumentation cost and model construction time. Initially the investment required is, typically US$ 50,000.00, which can be amortized over several tests.

FUTURE PERSPECTIVES New technological advances are expected with a new project, approved for implementation between 2008 and 2010, also sponsored by the AEB agency through VLS Associated Technology Projects, to perform tests with the sounding vehicle VS-40. The project title is “Implantação da Técnica de Tintas Sensíveis a Pressão no Túnel Transônico Piloto da ALA para Realização de Ensaios em Modelos de Veículos de Sondagem” (Implementation of the Pressure Sensitive Paint Technique in the Pilot Transonic Journal of Aerospace Technology and Management

Nowadays PSP is a well-established surface pressure measurement method, used in transonic wind tunnels in several research institutions around the world: NASA (Ames, Langley and Glenn), Boeing Seattle, Boeing St. Louis, Purdue University, Arnold Engineering Development Center (AEDC), University of Florida, Air Force Laboratory Wright-Patterson, in USA, British Aerospace (BAe) and DERA, in England, DLR, in Germany, ONERA, in France, National Aerospace Laboratory and JAXA Aerospace Research Center, in V. 1, n. 1, Jan. - Jun. 2009

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Japan, TsAGI, in Russia, among others. A review of PSP paints used for high-speed and unsteady aerodynamics was presented by Gregory et al. (2008), and it was shown that significant strides have been made in the development of PSPs for unsteady measurements, although there remains a substantial amount of work to be undertaken to further develop the technology. A lot of research has also been done in improving PSPs for use in low-speed conditions. One company, JAXA, has already achieved results with PSP in low-speed conditions for the development of aircrafts. The PTT wind tunnel work group is seeking new partnerships with universities and aeronautical companies to maintain and develop its research activities in the high speed realm. In this sense, a new project with Embraer has just come up with the aim of Silent Jet Research, sponsored by FINEP. The tunnel installation will have its capacity increased to perform tests on high speed jets over long periods inside a specially constructed fully instrumented anechoic chamber. Further applications are being considered for the PTT, like, new transonic airfoils development, research on unsteady aerodynamics, tests of special flight devices, such as trailing cones and anemometers. REFERENCES Bell, J. H., Schairer, E. T., Hand, L. A., Mehta, R. D., 2001, “Surface Pressure Measurements Using Luminescent Coatings.” Annu. Rev. Fluid Mech., 33, 55-206. David, S., Moraes, P. Jr., Uyeno, S., Cavalcanti, S. G., Nogueira, S. L., 1985, “Relatório do Grupo de Trabalho de Plano de Capacitação da Infra-Estrutura para Ensaios em Túnel de Vento,” Internal Report from IAE-ALA-TTS. Davis, M. W., Gunn, J. A., Herron, R. D., Kraft, E. M., 1986, “Optimum Transonic Wind Tunnel,” AIAA 14th Aerodynamic Testing Conference, 14, West Palm Beach, AIAA-86-0756-CP. Donovan, J. F., Morris, M. J., Pal, A., Benne, M. E., Crites, R. C., 1993, “Data Analysis Techniques for Pressure and Temperature-sensitive Paint,” AIAA Paper 93-0176. Presented at Aerosp. Sci. Meet. Exhib., 31st, Reno, NV. Divisão de Aeronáutica, 1986, “Projeto do Túnel Transônico/Supersônico 1o. Caderno Descritivo”, Internal Report from IAE-ALA-TTS.

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Goethert, B. H., 1961, “Transonic Wind Tunnel Testing”, Pergamon Press, New York. Gregory, J. W., Asai, K., Kameda, M., Liu, T., Sullivan, J. P., 2008, “A Review of Pressure-Sensitive Paint for HighSpeed and Unsteady Aerodynamics,” Journal of Aerospace Engineering, Vol. 222 Part G.

Falcão Filho, J. B. P., 2006, “Estudo Numérico do Processo de Injeção em um Túnel de Vento Transônico” ,Tese de Doutorado, ITA, São José dos Campos, 369 páginas.

GTTS, 1986, “Projeto do Túnel Transônico/Supersônico 1º Caderno Descritivo”, Internal Report from IAE-ALATTS, elaborado pelo Grupo de Trabalho para a Instalação dos Túneis Transônico e Supersônico no Brasil, São José dos Campos.

Falcão Filho, J. B. P., Ortega, M. A., 2007a, “Numerical Study of the Injection Process in a Transonic Wind Tunnel. Part I: The Design Point.” ASME, Journal of Fluids Engineering, Vol. 129, June, Issue 6, pp 682-694. DOI: 10.1115/1.2734236.

GTTS, 2009, “A Collection of Papers”, Internal Publication of IAE concerning the TTS Project, São José dos Campos classified.

Falcão Filho, J. B. P., Ortega, M. A., 2007b, “Numerical Study of the Injection Process in a Transonic Wind Tunnel. The Numerical Details”, Computers and Fluids, (approved for publication in 2007), available online in: www.sciencedirect.com. DOI: 10.1016/j.compfluid.2007. 10.015. Falcão, J. B. P., F., Ortega, M. A., 2008, “Numerical Study of the Injection Process in a Transonic Wind Tunnel. Part II: The Off-Design Points”, Computers and Fluids, (approved for publication). DOI: 10.1016/ j.compfluid.2008.09.009. Fico Júnior, N. G. C. R., 1991, “Simulação do Escoamento na Região do Flape de Reentrada de um Túnel de Vento Transônico,” Tese de Doutorado, ITA, São José dos Campos, 158 páginas. Fico Júnior, N. G. C. R., Ortega, M. A., 1993, “Numerical Prediction of Flap Losses in a Transonic Wind Tunnel”, AIAA Journal, Vol. 31, No. 1, p. 133-139. Goffert, B., Tagawa, G. B. S., Zanin, R. B., Reis, M. L. C. C., Falcão Filho, J. B. P., 2008a, “Ensaio de Calibração de Turbina de Inserção do Sistema de Extração Forçada de Massa do Túnel Transônico Piloto do IAE”, Anais do V Congresso Nacional de Engenharia Mecânica, CONEM2008, Salvador-Bahia, artigo 0941. Goffert, B., Truyts, C. F., Lima, D. S. A, Falcão Filho, J. B. P., 2008b, “Control of Injection System for the Pilot Transonic Wind Tunnel of IAE in Closed Circuit”, Proceedings of XII Brazilian Congress of Thermal Engineering and Sciences, ENCIT-2008 (accepted for publication), Belo Horizonte-MG, article 1-5054. Goffert, B., Falcão Filho, J. B. P., 2008, “Determinação do Coeficiente Politrópico Associado aos Reservatórios de Ar Comprimido do Túnel Transônico Piloto do IAE”, Anais do V Congresso Nacional de Engenharia Mecânica, CONEM2008, Salvador-Bahia, artigo 1029. Journal of Aerospace Technology and Management

Kavandi, J., Callis, J., Gouterman, M., Khalil, G., Wright, D., Green, E., Burns, D., McLachlan, B., 1990, “Luminescent Barometry in Wind Tunnels,” Review of Scientific Instruments, Vol. 61, No. 11, pp. 3340-3347. Liu, T., Sullivan, J. P., 2005, “Pressure and Temperature Sensitive paints”, Springer, Berlin. Liu, T., Campbell, B. T., Burns, S. P., Sullivan, J. P., 1997, “Temperature- and Pressure-sensitive Luminescent Paints in Aerodynamics”, Appl. Mech. Rev. 50(4): pp. 227-246. Miranda, R.V., 2004, “Instalação do Equipamento de Visualização Schlieren”, Relatório de Iniciação Científica sob orientação de Olympio Achilles de Faria Mello, ITA/FAPESP, São José dos Campos. Neiland, V. Y., 1997, “Scientific and Technical Proposals of TsAGI Concerning Concept of TTS Transonic Wind Tunnel”, Contracted Report from IAE-ALA-TTS to TsAGI Central Aero-Hydrodynamic Institute, Russia, Internal Report from IAE-ALA-TTS, classified. Nogueira, S. L., Passos, F. C., 1986a, “Relatório de Viagem à Europa”, Internal Report from IAE-ALA-TTS. Nogueira, S. L., Passos, F. C., 1986b, “Relatório de Viagem a Sverdrup”, Internal Report from IAE-ALA-TTS. Nogueira, S. L., Falcão Filho, J. B. P., Fico Júnior, N. G. C. R, Ortega M. A., 1988, “Injection Optimization and its Application to Wind Tunnels”, Proceedings of II Brazilian Congress of Thermal Sciences and Engineering, ENCIT88, Águas de Lindóia-SP, Vol. I, pp. 151-153. Nogueira, S. L., Falcão Filho, J. B. P., 1988, “Otimização no Projeto Conceitual dos Reservatórios para Túnel Supersônico de Sopro (tipo “Blowdown”)”, Anais do II Congresso Brasileiro de Ciências Térmicas e Engenharia, ENCIT-88, Águas de Lindóia-SP, Vol. I, pp. 154-156. Ortega, M. A., Escosteguy, J. P. C., 1988, “Simplified V. 1, n. 1, Jan. - Jun. 2009

Historical review and future perspectives for the Pilot Transonic Wind Tunnel of IAE

Analysis of the Flow in a Transonic Wind Tunnel Test Section with Ventilated Walls”, Proceedings of II Congresso Brasileiro de Ciências Térmicas e Engenharia, ENCIT-88, Águas de Lindóia, SP. Ortega, M. A.; Fico Jr., N. G. C. R., 1991, “Numerical Calculation of the Flowfield in the Flap Region of a Transonic Wind Tunnel Test Section”, Proceedings of XI COBEM, Congresso Brasileiro de Engenharia Mecânica, 1991, São Paulo, SP. Pope, A., Goin, K. L., 1978, “High-Speed Wind Tunnel Testing”, John Wiley & Sons, New York. Peterson, J. I., Fitzgerald, R. V., 1980, “New Technique of Surface Flow Visualization Based on Oxygen Quenching of Fluorescence,” Review of Scientific Instruments, Vol. 51, No. 5, pp. 670-671. Reed, T. D., Pope, T. C., Cooksey, J. M., 1977, “Calibration of Transonic and Supersonic Wind Tunnels”, NASA Contractor Report 2920. Reis, M. L., Castro, R. M., Falcão Filho, J. B. P., Mello, O. A. F., 2008, “Calibration Uncertainty Estimation for Internal Aerodynamic Balance”, Proceedings of 12th IMEKO TC1-TC7 joint Symposium on Man, Science & Measurement, September, Annecy, France. Steinle, F., Stanewsky, E., 1982, “Wind Tunnel Flow Quality and Data Accuracy Requirements”, AGARD Advisory Report No. 184. Sverdrup, 1987a, “Brazilian Transonic Wind Tunnel (TTS Project) Concept Definition Study,” prepared by Sverdrup Technology Inc. as a Contracted Report from IAE-ALATTS.

the Euler Equations”, Proceedings of XIV Congresso Brasileiro de Engemharia Mecânica, Baurú - SP. Viera, R., Azevedo, J. L. F., Fico Jr., N. G. C. R., Basso, E., 1998a, “Three Dimensional Simulations of the Flow in a Slotted Transonic Wind Tunnel. In: 10th International Conference on Finite Elements in Fluids,” Proceedings of 10th International Conference on Finite Elements in Fluids, Tucson Arizona. Viera, R., Azevedo, J. L. F., Fico Jr., N. G. C. R., Basso, E., 1998b, “Three Dimensional Flow Simulation in the Test Section of a Transonic Wind Tunnel”, Proceedings of XXI Congress of the International Council of the Aeronautical Sciences, Melbourne. Volan, A,, Alati, L., 1991, “A New Optical Pressure Measurement System”, Presented at Int. Congr. Instrum. Aerosp. Simul. Facil., 14th, New York, pp. 249-290. Wu, J. M., Moulden, T. H., 1976, “A Survey of Transonic Aerodynamics”, AIAA Paper no. 76-326, San Diego, California. Zanin, R. B., Reis, M. L. C. C., Falcão Filho, J. B. P., 2008a, “Análise da Uniformidade Longitudinal do Número de Mach na Seção de Testes do Túnel Transônico Piloto do IAE em Circuito Aberto”, Anais do V Congresso Nacional de Engenharia Mecânica, CONEM-2008, Salvador-Bahia, artigo 1031. Zanin, R. B., Braz, R., Avelar, A. C. B. J., Falcão Filho, J. B. P., 2008b, “Analysis of the Drier System of the Pilot Transonic Wind Tunnel of IAE”, Proceedings of XII Brazilian Congress of Thermal Engineering and Sciences, ENCIT-2008 (accept for publication), Belo Horizonte-MG, article 1-5117.

Sverdrup, 1987b, “Pilot Tunnel Detail Design for TTS Project,” Prepared by Sverdrup Technology Inc. as a Contracted Report from IAE-ALA-TTS. Tagawa, G. B. S., Reis, M. L. C. C., Falcão Filho, J. B. P., 2008, “Ajuste de Curva de Calibração de uma Balança Interna Multi-Componente”, Anais do V Congresso Nacional de Engenharia Mecânica, CONEM-2008, Salvador-Bahia, artigo 1124. Troyanovsky, I., Sadovskii, N., Kuzmin, M., Mosharov, V., Orlov, A., 1993, “Set of luminescence pressure sensors for aerospace research”, Sens. Actuators B, 11:2016. Truyts, C., Hemerly, E. M., Falcão Filho, J. B. P., 2008, “Identificação e Controle do Sistema de Injeção do Túnel Transônico Piloto”, Anais do XVII Congresso Brasileiro de Automática, CBA-2008, Juiz de Fora-MG. Viera, R., Azevedo, J. L. F., Fico Júnior, N. G. C. R., 1997, “Slotted Transonic Wind Tunnel Flow Simulation Using Journal of Aerospace Technology and Management

V. 1, n. 1, Jan. - Jun. 2009

Jairo Sciamareli* Instituto de Aeronáutica e Espaço São José dos Campos - Brasil sciamareli@iae.com.br

Jorge R. Da Costa Instituto de Aeronáutica e Espaço São José dos Campos - Brasil jrocosig@yahoo.com.br

Marta Ferreira K.Takahashi Instituto de Aeronáutica e Espaço São José dos Campos - Brasil martat@iae.cta.br

Koshun Iha Instituto Tecnológico de Aeronáutica São José dos Campos - Brasil koshun@ita.br

Agda Alvarenga V. Berdugo Instituto de Aeronáutica e Espaço São José dos Campos - Brasil agdaaavb@ifi.cta.br

Milton F. Diniz Instituto de Aeronáutica e Espaço São José dos Campos - Brasil miltond@iae.cta.br

Miriam H. Miyano Cognis Brasil Ltda Jacareí - Brasil Miriam.miyano@cognis.com

Carlos Ferreira Cognis Brasil Ltda Jacareí - Brasil carlos.ferreira@cognis.com

Otimização do processo de obtenção do pré-polímero metil azoteto de glicidila Resumo: Este trabalho descreve as ações e os resultados alcançados na otimização do processo de obtenção do pré-polímero Metil Azoteto de Glicidila (GAP). Foram obtidas amostras de poliepicloridrina (PECH) utilizando três diferentes catalisadores, BF3, SnCl4.5H2O e SnCl4 anidro, sob diferentes condições e cada amostra foi convertida, posteriormente, no pré-polímero GAP. Cada uma das amostras foi submetida às análises por FT-IR, determinação do índice de hidroxila e determinação da massa molar. Ao final, os resultados obtidos foram comparados com os valores previamente estabelecidos e determinado o melhor método de obtenção do GAP. Palavras-chave: Metil azoteto de glicidila, Síntese, Otimização, Caracterização, GAP.

Optimization of the process to obtain glycidyl azide polymer Abstract: This paper describes the action and results achieved during the optimization of Glycidyl Azide Polymer (GAP) characterization and process. Under different conditions, three different kinds of catalysts, BF3, SnCl4.5H2O and SnCl4 were used to obtain polyepichlorohydrin and each sample was converted into GAP. All the samples were submitted for characterization analysis by FT-IR and determination of molecular mass and hydroxyl value. Finally, results were compared and the best method to obtain GAP was determined. Keywords: Glycidyl azide polymer, Synthesis, Optimization, Characterization, GAP.

*autor para correspondência

INTRODUÇÃO Nos últimos anos tem sido constante a pesquisa de novos materiais que possam ser utilizados em propelentes. Buscam-se materiais mais energéticos, de maior estabilidade, menos agressivos ao meio ambiente, de menor custo, de mais fácil manuseio, entre outras características, que permitam um melhor desempenho de foguetes, mísseis e explosivos (Kawamoto, 2005, 2006). O Metil Azoteto de Glicidila (GAP) é um material energético considerado como material estratégico e de tecnologia avançada. A presença de grupos azida na molécula torna-o um composto energético, tendo o produto calor de formação positivo, da ordem de +975 kJ/kg a 293K (Kubota, 1988). Assim sendo, pode ser empregado na produção de propelentes energéticos e/ou propelentes “sem fumaça”, também conhecidos como “smokeless”. Para ____________________________________ Recebido: 24/03/09 Aceito: 27/04/09 Journal of Aerospace Technology and Management

estes casos, é desejável que o GAP tenha uma massa molar semelhante à dos pré-polímeros utilizados na produção de propelentes, ou seja, entre 2000 e 3000 g/mol (Ochoa Gomez, 1994). O estudo de obtenção de azido polímeros com terminações hidroxílicas teve início em meados da década de 1970 e, mais especificamente o GAP, começou a ser desenvolvido no final daquela década, a pedido da Força Aérea NorteAmericana, interessada em utilizá-lo na composição de propelentes para mísseis táticos e balísticos (Frankel, 1992). O GAP é produzido em duas etapas: na primeira, a partir da reação de homopolimerização da epicloridrina é obtido o intermediário poliepicloridrina (PECH) e este, reagindo com azida metálica dá origem ao GAP. A reação de obtenção da poliepicloridrina ocorre por meio V. 1, n. 1, Jan. - Jun. 2009

Sciamareli, J. et al.

de mecanismos diferentes, de acordo com o catalisador utilizado: mecanismo de monômero ativado quando se utiliza o trifluoreto de boro (BF3) e mecanismo catiônico e coordenativo quando se utiliza o tetracloreto de estanho (SnCl4). Pode ocorrer, ainda, outro mecanismo (Francis, 2003), chamado de término de cadeia ativada, em maior ou menor grau, proporcionando a formação de compostos cíclicos. A formação destes compostos cíclicos é indesejada, visto que são contaminantes no produto final. Isto acontece quando uma molécula de PECH em crescimento reage com uma molécula de epicloridrina e mantém o anel epóxido protonado. Ocorre um rearranjo molecular, com formação de composto cíclico (Kubisa, 1999). Após ser formada, a parte cíclica se desprende da molécula, permanecendo no meio como contaminante. As reações de obtenção da poliepicloridrina e GAP são mostradas nas Fig. 1 e 2. A etapa de obtenção da PECH é de fundamental importância, pois, praticamente todas as propriedades mecânicas do GAP são funções da PECH, tais como massa molar, índice de hidroxila e funcionalidade. Nesta etapa é muito importante utilizar reagentes os mais isentos possíveis de água, já que esta pode funcionar como iniciador e/ou terminador de cadeia, prejudicando a obtenção do pré-polímero com a massa molar planejada.

produzido, houve a necessidade de determinar a massa molar do polímero obtido. Foi estabelecido como objetivo obter o GAP com massa molar média (Mn) entre 2200 e 3000 g/mol e índice de hidroxila entre 0,75 e 0,90 mmol/g. Um dos caminhos para atingir tal objetivo foi a variação nas razões iniciador/monômero e catalisador/monômero. Outro ponto abordado foi o método utilizado para obtenção do produto. Conforme o catalisador utilizado, tetracloreto de estanho ou o trifluoreto de boro eterato na obtenção da PECH, há métodos de síntese modificados um em relação ao outro. Os catalisadores citados fazem parte de um grupo de compostos conhecidos como ácidos de Lewis, que são caracterizados por acomodar um par eletrônico na molécula, sendo chamados de catalisadores catiônicos (Manzara, 1992). Foram reproduzidos os dois métodos e comparados os resultados finais para melhor avaliação de cada um, no que concerne ao rendimento de reação e características químicas do produto obtido. Para a caracterização da massa molar existem métodos descritos em artigos já publicados (Biedron, 1991), bem como métodos de análise do índice de hidroxila e de funcionalidade.

EXPERIMENTAL

Figura 1: Reação de obtenção da PECH.

Figura 2: Reação de obtenção do GAP.

Neste trabalho, houve a intenção de aperfeiçoar o processo de obtenção do GAP conduzido anteriormente (Sciamareli, 2009), melhorando o rendimento das reações de obtenção e caracterizando os produtos obtidos por meio de análises instrumentais. Além de conseguir maior transformação de reagentes em produtos de reação, melhorando o rendimento da reação, outra preocupação foi com aquela que é considerada uma importante propriedade de um polímero, sua massa molar, que tem forte influência nas propriedades mecânicas do material elastomérico (Davenas, 1993). Assim sendo, pequenas modificações no processo de obtenção do produto foram efetuadas para atingir os resultados desejados. Para cada batelada de produto Journal of Aerospace Technology and Management

Para obter o GAP com as características citadas, foram testados 3 catalisadores diferentes na etapa de obtenção do intermediário poliepicloridrina: tetracloreto de estanho anidro (SnCl4), tetracloreto de estanho pentahidratado (SnCl4.5H2O) e trifluoreto de boro eterato (BF3) e feitas variações nas razões iniciador/monômero e catalisador/ monômero. Além destes, foram escolhidos como reagentes o butanodiol 1,4 como iniciador, o diclorometano e dicloroetano como solventes para obtenção da PECH, o ácido trifluoracético e a epicloridrina. Alguns reagentes selecionados foram logo abandonados, como o 1,4 bis hidroximetil ciclohexano, por ser extremamente deliquescente e o etileno-glicol, por favorecer a formação de compostos cíclicos (Biedron, 1991). Ainda, na parte de tratamento das amostras de PECH, foram utilizados ácido clorídrico, EDTA tetrasódico, hidróxido de amônio e carbonato de sódio. Para a reação de obtenção do GAP, além da PECH, foram utilizados dimetil formamida (DMF) e dimetil acetamida (DMA) como solventes e azida de sódio. A reação de obtenção da PECH implica na utilização de diferentes métodos de síntese, conforme o catalisador utilizado. Estes métodos estão descritos em relatório (Sciamareli, 2007). Cada uma das amostras de PECH e GAP obtidas foi submetida a análise por FT-IR, análise para a determinação de massa molar e do índice de hidroxila. V. 1, n. 1, Jan. - Jun. 2009

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Os seguintes equipamentos e condições foram utilizados para a determinação das características das amostras: espectrofotômetro Spectrum One da Perkin Elmer (condições básicas: região 4000-400cm-1, resolução 4cm-1, ganho 1, 20 varreduras); cromatógrafo líquido marca Waters (condições básicas: colunas styragel HR 0.5, 1.0, 2.0 e 3.0, colunas em série, tetrahidrofurano como fase móvel, detecção por índice de refração e concentração de amostra de 20mg/mL de solvente, forno a 40ºC e padrões de poliestireno) e titulador potenciométrico marca Metrohm, modelo Titrando 836 com eletrodo para meio não-aquoso. RESULTADOS E DISCUSSÕES Síntese dos produtos A poliepicloridrina foi obtida utilizando os catalisadores citados. De modo geral, utilizando a proporção iniciador/catalisador considerada a mais adequada, como é mostrado na Tab. 1, o rendimento da reação de obtenção da PECH situa-se próximo de 90%.

A Tabela 3 exibe os dados referentes às sínteses de GAP, como rendimento de reação e PECH utilizada. Tabela 3: Rendimento da reação de obtenção do GAP. Amostra GAP 01/07 GAP 02/07 GAP 03/07 GAP 04/07 GAP 05/07 GAP 06/07 GAP 07/07 GAP 08/07 GAP 09/07 GAP 10/07 GAP 11/07 GAP 12/07

Rendimento da reação 77,0% 77,0% 77,5% 81,3% 80,8% 70,0% 55,0% 55,0% 77,3% 71,0% 81,7% 85,0%

PECH utilizada PECH 01/07 PECH 02/07 PECH 03/07 PECH 06/07 PECH 07/07 PECH 08/07 PECH 09/07 PECH 10/07 PECH 11/07 PECH 12/07 PECH 13/07 PECH 14/07

Caracterização do produto Tabela 1: Proporção iniciador/catalisador considerada mais adequada. Catalisador utilizado

BF3

SnCl 4

SnCl4 .5H2O

Proporção adequada

2:1

1:1

2:1

A reação de obtenção do GAP possui um rendimento entre 70 e 80% quando se utiliza o dimetil formamida (DMF) como solvente e em torno de 55% quando se utiliza o dimetil acetamida (DMA). Além disso, a utilização deste último dificulta muito a separação das fases orgânica e aquosa nesta etapa. A Tabela 2 exibe dados referentes às sínteses de PECH, catalisador utilizado, proporção deste em relação ao iniciador e rendimento de reação. Tabela 2: Dados referentes à síntese das amostras de PECH. Amostra PECH 01/07 PECH 02/07 PECH 03/07 PECH 04/07 PECH 05/07 PECH 06/07 PECH 07/07 PECH 08/07 PECH 09/07 PECH 10/07 PECH 11/07 PECH 12/07 PECH 13/07 PECH 14/07

Proporção Catalisador iniciador/catalisador utilizado BF3 BF3 SnCl4.5H2O SnCl4 SnCl4 SnCl4 SnCl4.5H2O SnCl4 SnCl4 SnCl4 SnCl4.5H2O SnCl4 SnCl4.5H2O BF3

2:1 2:1 2:1 2:1 4:1 1:1 2:1 1:1 1,5:1 1:1 3:1 1:1 2:1 1,5:1

Journal of Aerospace Technology and Management

Rendimento 92,0% 88,9% 93,5% 70,0% 32,7% 88,0% 92,3% 81,5% 94,4% 88,0%* 93,7% 91,3% 86,9% 84,1%

Análise FT-IR As principais absorções espectofotométricas da epicloridrina caracterizadas com base em tabelas de absorção de grupos funcionais (Silverstein, 1991) estão em torno de: 3063, 3004, 2963, 2926, 2874 e 2850cm-1, estiramento de grupos CH e CH2, 1267cm-1, vibração do anel epoxídico e deformação tipo sacudida de grupos CH2Cl; 1430cm-1, deformação no plano de grupos CH2; 926 e 852 cm-1, anel epóxido; 906 e 760cm-1, balanço de grupos CH2 e CCl; 723cm-1, Ccl. Quando da formação da poliepicloridrina, são esperados o desaparecimento das absorções em 1267, 926 e 852cm-1, todas referentes a abertura do anel epóxido. Já na poliepicloridrina (PECH), caracterizada pela unidade repetida CH(CH2Cl)CH2O, são esperados o aparecimento das absorções em torno de 3460-3480cm-1, região de estiramento de grupos OH e em 1110-1120cm-1, região de grupos COC de éter. A Figura 3 exibe os espectros da epicloridrina (A) e das poliepicloridrinas obtidas com os 3 diferentes catalisadores (B, C e D). Pode se observar nos espectros o desaparecimento e o surgimento das absorções esperadas, o que confirma a obtenção de poliepicloridrina por meio dos diferentes métodos e catalisadores empregados. Nos espectros das poliepicloridrinas obtidas com a utilização do catalisador SnCl4, anidro e hidratado, aparece uma banda de absorção em torno de 1780cm-1, região de absorção de grupos carbonila. Este grupo não pertence à cadeia. Uma possível hipótese para sua presença é a presença de resíduo do co-catalisador ácido trifluoracético ou de um derivado deste. V. 1, n. 1, Jan. - Jun. 2009

Sciamareli, J. et al.

No espectro do GAP é esperado o desaparecimento da absorção em torno de 748cm-1, região de grupos CH2Cl da PECH e o surgimento de bandas de absorção na região de 2100 e 2280cm-1, referente a estiramento de grupos CH2N3. A Fig. 4 exibe os espectros das poliepicloridrinas obtidas com os três diferentes catalisadores (A, C e E) e das amostras de GAP obtidas com cada uma destas poliepicloridrinas (B, D e F).

A e B são, respectivamente, os espectros FT-IR da PECH 01/2007 CLS e seu correspondente GAP 01/2007 CLS, C e D da PECH 12/2007 CLS e GAP 10/2007 CLS e E e F da PECH 13/2007 CLS e GAP 11/2007 CLS. Como já era previsível, ocorre o aparecimento e o desaparecimento das bandas citadas, confirmando a obtenção do GAP. Para as outras amostras foi observado o mesmo resultado, evidenciando que, em todas as variações estudadas, a PECH e o GAP foram obtidos (Takahashi, 2007), porém, com características diferentes, tais como, índice de hidroxila e massa molar, embora não apresentem alterações espectrofotométricas. Massa Molar A massa molar das amostras foi determinada por meio da técnica Cromatografia de Permeação de Gel (GPC).

A Tabela 4 exibe os valores de massa molar numérica média (Mn), massa molar ponderal média (Mw) e massa molar no pico máximo (MP) na faixa de maior extensão de massa molar, além da polidispersão. Tabela 4: Valores de massa molar das diferentes amostras de PECH e GAP. 4000.0

3600

3200

2800

2400

2000

1800 1600 cm-l

1400

1200

1000

800

600

400.0

Figura 3: Espectros FT-IR da: (A) epicloridrina, marca Fluka (B) PECH obtida com catalisador BF3; (C) PECH obtida com catalisador SnCl4 anidro (D) PECH obtida com catalisador SnCl4.5H2O.

4000.0

3600

3200

2800

2400

2000

1800 1600 cm-l

1400

1200

1000

800

600

400.0

Figura 4: Espectros FT-IR: (A) e (B) PECH 01/2007 e seu correspondente GAP 01/2007 CLS; (C) e (D) PECH 12/2007 e seu correspondente GAP 10/2007 CLS; (E) e (F) PECH 13/2007 e seu correspondente GAP 11/2007 CLS. Journal of Aerospace Technology and Management

Amostra

Polidispersão

PECH 01/07 PECH 02/07 PECH 03/07 PECH 04/07 PECH 05/07 PECH 06/07 PECH 07/07 PECH 08/07 PECH 09/07 PECH 10/07 PECH 11/07 PECH 12/07 PECH 13/07 PECH 14/07 GAP 01/07 GAP 02/07 GAP 03/07 GAP 04/07 GAP 05/07 GAP 06/07 GAP 07/07 GAP 08/07 GAP 09/07 GAP 10/07 GAP 11/07 GAP 12/07

1928 1993 1643 1719 2343 1897 2400 1881 2362 2926 2905 1669 1896 1662 2044 2129 2242 2002 2724 2347 2709

2169 2313 2744 2821 2737 2264 2825 2477 3269 3289 3284 2404 3175 2363 3131 3091 3129 2298 3128 2724 3758

2289 2170 2230 2990 1244 2825 2272 2745 3056 3009 2171 2965 2555 3061 2650 2586 2545 3085 2470 3216 2800 2666 2342 3338 2809 3361

1,12 1,16 1,67 1,64 1,17 1,19 1,18 1,32 1,38 1,12 1,13 1,44 1,67 1,42 1,53 1,45 1,40 1,15 1,15 1,16 1,39

V. 1, n. 1, Jan. - Jun. 2009

Otimização do processo de obtenção do pré-polímero metil azoteto de glicidila

As Figuras 5 e 6 mostram, respectivamente, os cromatogramas para as amostras PECH 12/2007 CLS e GAP10/2007 CLS. Também neste caso, o mesmo tipo de resultado foi encontrado para as outras amostras. De acordo com as figuras citadas, a amostra de PECH 12/CLS 2007 tem massa molar (Mn) em torno de 2400 g/mol, com polidispersão de 1,18 e a amostra de GAP 10/2007 CLS tem massa molar (Mn) em torno de 2724 g/mol, com polidispersão de 1,15. Esses valores indicam, neste caso específico, que o produto precursor e o GAP obtido têm moléculas de tamanhos próximos em grande parte da extensão da amostra e dentro dos parâmetros requeridos.

Índice de hidroxila As amostras de PECH obtidas com o catalisador BF3 (PECH 01/2007 CLS e PECH 02/2007 CLS) e as respectivas amostras de GAP (GAP 01/2007 CLS e GAP 02/2007 CLS) possuem índice de hidroxila dentro da faixa requerida neste estudo, no caso 0,75 a 0,90 mmol/g. As amostras de PECH obtidas com o catalisador SnCl4.5H2O e seus respectivos GAP apresentaram, todas, índice de hidroxila superior à faixa desejada, de modo geral, de 0,92 a 1,1 mmol/g enquanto as amostras obtidas com SnCl4 anidro e seus respectivos GAP apresentaram teor de hidroxila entre 0,74 e 0,82 mmol/g, dentro da faixa requerida.

Auto-Scaled Chromatogram

40.00

30.00

As amostras de PECH obtidas com catalisador BF3, juntamente com seus respectivos GAP, apresentam massa molar com valores muito variados, o que significa que as amostras têm moléculas de “tamanhos” muito diferentes, sendo que menos de 40% delas têm a massa molar dentro da faixa desejada.

20.00

A Tabela 5 exibe os dados referentes aos índices de hidroxila de cada uma das amostras.

10.00

Tabela 5: Índice de hidroxila das amostras obtidas.

0.00

5.00

10.00

15.00

20.00

25.00 Minutes

30.00

35.00

40.00

45.00

50.00

Figura 5: Cromatograma da amostra PECH 12/2007 CLS.

Auto-Scaled Chromatogram 60.00

50.00

40.00

30.00

20.00

10.00

0.00

5.00

10.00

15.00

20.00

25.00 Minutes

30.00

35.00

40.00

45.00

50.00

Figura 6: Cromatograma da amostra GAP10/2007 CLS.

A amostra PECH 12/2007 CLS foi obtida com catalisador SnCl4 anidro na proporção 1:1 iniciador/ catalisador. As amostras de PECH, e seus respectivos GAP, obtidas com a utilização de catalisador SnCl4.5H2O apresentam, de modo geral, massa molar (Mn) na faixa de 1650 a 2000 g/mol, abaixo do mínimo esperado, que é 2200 g/mol. Não obstante, têm baixa polidispersão, a melhor dentre as amostras estudadas. Journal of Aerospace Technology and Management

Amostra

Índice de hidroxila (mmol/g)

0,80±0,01 0,79±0,01 1,05±0,02 1,14±0,03 1,19±0,05 0,82±0,01 0,95±0,04 0,78±0,01 0,80±0,01 0,74±0,01 0,97±0,02 0,78±0,02 0,93±0,01 0,68±0,01 0,81±0,01 0,81±0,01 1,06±0,02 0,82±0,02 1,05±0,01 0,80±0,01 0,95±0,01 0,94±0,02 1,09±0,01 0,82±0,03 0,98±0,08 0,66±0,04

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Sciamareli, J. et al.

CONCLUSÕES Para obter o GAP dentro dos parâmetros esperados, rendimento das reações superior a 50%, massa molar entre 2200 e 3000 g/mol e índice de hidroxila entre 0,75 e 0,90 mmol/g, deve-se utilizar o SnCl4 anidro como catalisador na proporção 1:1 iniciador /catalisador. A utilização do catalisador SnCl4.5H2O, nas condições estudadas, leva a obtenção de um produto com massa molar abaixo do especificado e índice de hidroxila acima.

Ochoa Gomez, J. R. et al, 1994, “Process for Obtaining a Hydroxyl-Ended Glycidil Azine Polymer”, U.S. Pat 5,319,037. Sciamareli, J. et al, 2009, “Síntese e Caracterização do Polímero Energético Metil Azoteto de Glicidila (GAP) Via Análises Instrumentais” Polímeros: Ciência e Tecnologia (no prelo). Sciamareli, J., 2007, “Processo de Otimização da Obtenção e Caracterização do Glicidil Azida Polimérico”, IAE, São José dos Campos, Brazil (DOC.AQI-010-RT/07).

A utilização do catalisador BF3, também nas condições estudadas, nos leva a obtenção de um produto com massa molar muito diversificada, ou seja, “tamanhos” de moléculas muito diferentes entre si.

Silverstein, R. M., 1981, “Spectrometric Identification of Organic Compounds”, John Wiley & Sons, New York, USA.

REFERÊNCIAS

Takahashi, M. F. K., 2007, “Análise por FT-IR de amostras de PECH E GAP”, IAE, São José dos Campos (IR/M09/07) (IR/M13/07) (IR/M21/07).

Biedron, T. et al;, 1991, “Polyepichlorohydrin Diols Free of Cyclic: Synthesis and Characterization”, Journal of Polymer Science, Vol. 29, pp.619-628. Davenas, A., 1993, “Composite Propellants”, In: Davenas, A. (ed.). Solid Rocket Propulsion Technology, Pergamon Press, London, England, Cap. 10, pp.415-475. Francis, A. U. et al, 2003, “Structural Characterization of Hydroxyl Terminated Polyepichlorohydrin Obtained Using Boron Trifluoride Etherate and Stannic Choride as Initiators”, European Polymer Journal, Vol. 39, pp.831841. Frankel, M. B.; Grant, L. R.; Flanagan, J. E., 1992, “Historical Development of Glycidyl Azide Polymer”, Journal of Propulsion and Power, Vol. 8, No.3, pp. 560-563. Kawamoto, A. M. et al., 2005, “Synthesis and Characterization of Energetic Oxetane-Oxirane Polymers for Use In Thermoplastics Elastomers Binders Systems”, Proceedings of the 36th International Annual Conference of ICT, Karlshure, Germany. Kawamoto, A. M. et al., 2006, “Synthesis and Characterization of Energetic ABA-Type Thermoplastics Elastomers for Propellant Formulations”, Proceedings of the 37th International Annual Conference of ICT, Karlshure, Germany. Kubisa, P.; Penczek, S., 1999, “Cationic Activated Monomer Polymerization of Heterocyclic Monomers”, Progress in Polymer Science, Vol. 24, pp.1409-1437. Kubota, N.; Sonobe, T., 1988, “Combustion Mechanism of Azide Polymer”, Propellants, Explosives, Pyrotechnics, Vol.13, pp. 172-177 . Manzara, A. P.; Johnnessen, B., 1992, “Primary HydroxylTerminated Polyglycidyl Azide”, U.S. Pat 5,164,521. Journal of Aerospace Technology and Management

V. 1, n. 1, Jan. - Jun. 2009

Aparecida M. Kawamoto* Institute of Aeronautics and Space São José dos Campos - Brazil cidak@iae.cta.br

José Irineu S.Oliveira Institute of Aeronautics and Space São José dos Campos - Brazil jirineu@iae.cta.br

Rita de Cássia L. Dutra Institute of Aeronautics and Space São José dos Campos - Brazil chefia.aqi@iae.cta.br

Luis Claudio Rezende Institute of Aeronautics and Space São José dos Campos - Brazil lcrezende@iae.cta.br

Thomas Keicher Institut Chemische Technologie Pfinztal - Germany thomas.keicher@ict.fhg.de

Horst Krause Institut Chemische Technologie Pfinztal - Germany kr@ict.fhg.de * author for correspondence

Synthesis and characterization of energetic thermoplastic elastomers for propellant formulations Abstract: Synthesis and characterization of energetic ABA-type thermoplastic elastomers for propellant formulations has been carried out. Following the working plan elaborated, the synthesis and characterization of Poly 3bromomethyl-3-methyl oxetane (PolyBrMMO), Poly 3- azidomethyl-3-methyl oxetane (PolyAMMO), Poly 3,3-bis-azidomethyl oxetane (PolyBAMO) and Copolymer PolyBAMO/AMMO (by TDI end capping) has been successfully performed. The thermoplastic elastomers (TPEs) were synthesized using the chain elongation process PolyAMMO, GAP and PolyBAMO by diisocyanates. In this method 2.4-toluene diisocyanate (TDI) is used to link block A (hard and monofunctional)) to B (soft and di-functional). For the hard A-block we used PolyBAMO and for the soft B-block we used PolyAMMO or GAP.This is a joint project set up, some years ago, between the Chemistry Division of the Institute of Aeronautics and Space (IAE) - subordinated to the Brazilian Ministry of Defense and the Fraunhofer Institut Chemische Technologie (ICT), in Germany. The products were characterized by different techniques as IR- and (1H,13C)NMR spectroscopies, elemental and thermal analyses. New methodologies based on FT-IR analysis have been developed as an alternative for the determination of the molecular weight and CHNO content of the energetic polymers. Key words: Energetic thermoplastic elastomers, PolyAMMO, PolyBAMO, Copolymer PolyBAMO/AMMO, Propellants.

LIST OF SYMBOLS AMMO BA BAMO BDO BrMMO CHN CsI DSC E-TPE FT-IR GAP GPC IR KBr Mw Mn NMR N3 PolyAMMO PolyBAMO PolyBBrMO

3-Azidomethyl-3-methyl oxetane Benzyl Alcohol 3,3-Bis-azidomethyl oxetane Butanediol 3-Bromomethyl-3-methyl oxetane Elemental analysis Cesium Iodide Differential scanning calorimetry Energetic thermoplastic elastomer Fourier transform infrared spectroscopy Glycidyl azido polymer Gel permeation chromatography Infrared spectroscopy Potassium bromide Molecular weight (average weight) Molecular weight (average number) Nuclear magnetic resonance Azide Polymer of 3-azidomethyl-3-methyl oxetane Polymer of 3,3-bis-azidomethyl oxetane Polymer of 3- bromomethyl-3-methyl oxetane

____________________________________ Received: 14/04/09 Accepted: 07/05/09 Journal of Aerospace Technology and Management

ppm TDI THF δ

Parts per million Toluene di-isocyanate Tetrahydrofuran Chemical shift

INTRODUCTION Modern solid explosive compositions, like propellants, generally consist of particulate solids such as fuel material (metal powders), oxidizers and explosives, which are held together by an elastomeric binder matrix. In this binder matrix the energetic solid filler composition is embedded and immobilized to achieve defined combustion characteristics and also to keep the propellant in a fixed geometry. During combustion, the binder acts as fuel but with the restriction that the energy output from the combustion of the binder is much lower in comparison to the energy output from the combustion of metal powders. Therefore, the use of binder materials, which are energetic itself, is an attempt to improve the performance of propellants. On the other hand, with energetic binder systems the filler content can be reduced without any loss in performance but with the benefit of decreased signature caused from the combustion products of the solid fillers (metal powders, halogenated oxidizers). Another benefit in V. 1, n. 1, Jan. - Jun. 2009

Kawamoto, A.M. et al.

the reduced filler content might be sensitivity reduction. Conventional binder systems consist of liquid prepolymers that are cross-linked by chemical curing agents. These systems have to be cast within a short time frame after adding the curative, which sets some restriction for the industrial processing. Additionally, the once cured binder material cannot be reused or recycled because the curing reaction is irreversible (Archibald et al., 1997, Wardle et al., 1996). Energetic thermoplastic elastomers (E-TPE) are one possibility to overcome all these disadvantages. Thermoplastic elastomers are block copolymers that exhibit rubber-like elasticity without requiring chemical cross-linking, which present ABA, AB, or (AB)n structure, where A and B are the hard and the soft segments respectively. The hard segment (glassy or semi crystalline at room temperature) gives its thermoplastic behavior, whereas the soft segment (rubbery at room temperature) gives the elastomeric behavior. The thermoplastic behavior results from the formation of rigid domains by chain association due to reversible interaction such as dipoledipole interactions, hydrogen bonding, etc. The soft segments are incompatible with the hard segments, hence leading to a microphase separation. Therefore, a thermoplastic elastomer behaves like a rubber because it is cross-linked in the same manner as a conventional elastomer, but with reversible physical cross-links instead of chemical ones. For processing, the E-TPE can be heated above the transition temperature to melt it or it can be dissolved in a solvent, then mixed with other components of a formulation, and processed. Cooling the E-TPE or evaporating the solvent allows the broken physical crosslinks to re-form and the elastomeric properties are recovered. Depending on the processing technique used to prepare a Gun or Rocket Propellant, or a High Explosive formulation, steps such as cooling or evaporating the solvent can allow the E-TPE physical bonds to re-form and give the final material. This also means that a formulation containing E-TPE, when obsolete, could be heated above the transition temperature or dissolved, allowing for the recovery of the ingredients that could be separated. Therefore, the use of E-TPE will lead to recyclable energetic materials (Sanderson and Edwards, 2000, Manser and Miller, 1993, Manser et al., 1996, Saegusa et al., 1970). Energetic Thermoplastic Elastomers (E-TPEs), have exhibited their wide value application in the research development of novel binders for Solid Rocket Propellants. They are considered as crosslinked polymers that provide a matrix which binds the explosive ingredients together with particulate particle oxidizer, burning rate catalyst, plasticizers and so forth, resulting in a tough elastomeric three-dimensional network structure capable of absorbing and dissipating energy from hazardous stimuli. They represent the next generation of energetic binders. Since they mimic the elastomeric behavior of conventional binders, they can lead to insensitive munitions and increase the energy of the formulations. They can also be Journal of Aerospace Technology and Management

recuperated, which leads to recyclable munitions (Murali et al., 2004). Another advantage of thermoplastic elastomers over the conventional binders is that they do not need to be cured, so there is no possibility of missed batches. They are reusable and are reprocessed a number of times, and can also be solvated by organic solvents, so surplus material can be recuperated, cleaned and used again As for the use in Solid Rocket Propellant the E-TPE's and their synthesis should present the following properties (Provatas, 2000). 

Molecular weight control



Reproducible molecular weight



Low dispersity



Low glassy transition temperature



Good and easy-to-handle processibility



Energetic characteristics



Low sensitivity against mechanical stimulus and shock wave impact



Good thermal stability



Good compatibility with other propellant ingredients

However, many non energetic commercially available Thermoplastic Elastomers fail to meet the aforementioned important requirements expected in propellant formulations, particularly that of being processible below approximately 120°C. It has been desirable that a Thermoplastic Elastomer polymer for use as binder in a high energy system should have a melting point temperature of between 60°C to 120°C. The 60°C is related to the fact that the propellant composition may be subject to somewhat elevated temperatures during storage and use, and it is undesirable that significant softening of the propellant composition occurs. The 120°C is determined by the instability of many components ordinarily used in propellant compositions, particularly oxidizers, explosives and energetic plasticizers (Hsiue et al., 1994). An attractive approach to high energy and low sensitivity propellants involves the use of energetic oxetane prepolymers (Wardle, 1989). These binders act as energy partitioning agents by allowing an energetic formulation to maintain a constant energy level at lower solid percentages. Partitioning a portion of the formulation energy into the binder phase is predicted to result in significant improvements in the formulation. The lower solid is V. 1, n. 1, Jan. - Jun. 2009

Synthesis and characterization of energetic thermoplastic elastomers for propellant formulations

predicted to result in improved processing mechanical properties, and reduced friability (Wardle, 1989).

reaction is represented by the equation:

Copolymers are generally advantageous relative to homopolymers because of the presence of an additional oxetane or other monomer unit(s), even in small amounts, which substantially reduces chain regularity. Homopolymers with a high degree of chain regularity exhibit substantial chain folding, resulting in a compact structure which tends to be crystalline or highly viscous (Sanderson and Edwards, 2000).

A (monomer)

+B (monomer)

A high energy binder based on block copolymers of ABA, AB, or (AB)n structure of cylic ethers and oxetanes and derivatives, will be examined to determine whether the postulated improvements for the binder will be possible in solid rocket propellants. Attention has been particularly focused on polymers that contain the energetic azido group. The monomer or combination of monomers of the A block are selected to prove a crystalline structure at usual ambient temperature, whereas the monomer or combination of monomer of the B block are selected to ensure an amorphous structure at usual ambient temperature.

A (active polymer)

AB (active polymer) +A (monomer) ABA triblock polymer

Alternatively, a difunctional initiator could be used to initiate the polymerization of the B block. When the A block is added, the polymerization would proceed from both active ends of the B block. The reaction is represented by the equation: B (monomer)

B (difunctional active polymer) +A (monomer) ABA triblock polymer

By selecting the appropriate block functionality or by repetition of steps, these methods are also proposed as suitable for producing (AB)n polymers.

The A and B blocks of such polymers are mutually miscible in a polymer melt. The melt viscosities of such a TPE decrease rapidly as the temperature is raised above the melting point of the crystalline A blocks, contributing to its processibility.

Both of these methods to produce TPEs have been proven to be satisfactory. Joining blocks A and B is found to be much better, as described by Wardle et al. (1996).

Furthermore, a thermoplastic elastomer based on crystalline domains exhibits advantageous solventresistance and minimal setup shrinkage. Such a TPE can be formulated to have a melting temperature which falls within a desirable 60째C to 120째C range.

According to Wardle (1989), a three stage method is provided for forming thermoplastics that have polyether crystalline A blocks and B blocks that are individually synthesized. The A blocks and B blocks are each separately end-capped with a diisocyanate, in which one isocyanate is substantially more reactive with active groups on the blocks than is the other isocyanate group.

Two methods can be used to prepare these TPEs. One method to get the ABA triblock or (AB)n polymers may be to join them together through a block linkage technique in which a linking moiety, such as isocyanate, is reacted with both ends of the middle (B) block and the end (A) blocks are subsequently reacted with the linking group (x). Generally the reaction is:

Finally, the end-capped blocks are mixed and reacted with a difunctional linking chemical, in which each function on the linking chemical is isocyanate reactive and sufficiently unhindered to react with a free isocyanate group in a capped block. However, to link difunctional A and B bocks and form exclusively ABA elastomers by controlling the blocks' stoichiometry is statistically unrealistic.

+2A B + 2x

xBx

AxBxA polymer

The other method is when the ABA copolymer is formed by systematic monomer addition. For example, the A monomer may be reacted with an initiating adduct to form an A block by cationic polymerization and the reaction is allowed to proceed until monomer A is substantially exhausted. Then, the monomers of block B are added and polymerization proceeds from the active end of block A. When the monomers of block B are substantially exhausted, additional monomers of block A are added, and polymerization proceeds for the active end of block B. The Journal of Aerospace Technology and Management

Therefore the same author in another patent (Wardle et al., 1996) developed a novel one pot method for the synthesis of the copolymer. After individual synthesis of monofunctional A blocks and di functional B blocks, the monofunctional crystalline A block is end-capped with a difunctional isocyanate that has one of the isocyanate groups more reactive than the other one. Therefore the more reactive isocyanate group reacts to the functional group of A block, leaving the less reactive isocyanate group free and unreacted. Thereafter, adding the difunctional B blocks to the end-capped A blocks at approximately the stoichiometric ratios that they are intended to be present in the Thermoplastic Elastomer, the free and unreacted V. 1, n. 1, Jan. - Jun. 2009

Kawamoto, A.M. et al.

isocyanate group on the end-capped monofunctional A block reacts with a functional group of the B blocks to produce ABA Thermoplastic Elastomers. For the synthesis of TPEs, first it is necessary to synthesize the polymer that will serve as the A block, which is crystalline in nature and with a relatively elevated melting point, i.e., between about 60oC and 120oC, preferably near 80oC and then the synthesis of a polymer, which is to serve as the B block, which is amorphous in structure, with a glass transition temperature (Tg) below about -20oC and preferably below -40oC. The property of the block polymer depends on the molecular weights of the individual blocks and the total molecular weights. Typically the A blocks have molecular weights ranging from about 3000 to about 12500, whereas the B blocks have molecular weights ranging from about 5000 to about 50.000. Preferably, the A blocks are shorter than B blocks, the total molecular weight of the A blocks typically range from about ½ to 1 times the molecular weight of the B blocks in an ABA triblock copolymer. The decomposition and combustion products of polyBAMO contain relatively high concentrations of fuel fragments such as C(s), H2, and CO. Thus, the addition of oxidizers in combination with azide polymers enables the propellant a better performance, such as high specific impulse. In 2004, a joint project was set up between the Chemistry Division of the Institute of Aeronautics and Space (IAE) subordinated to the Brazilian Ministry of Defense - and the Fraunhofer Institut Chemische Technologie (ICT), in Germany, with the goal to synthesize some energetic binders that could have several applications, including their use in propellants. Therefore the compounds Poly 3bromomethyl-3-methyl oxetane (PolyBrMMO), Poly 3azidomethyl-3-methyl oxetane (PolyAMMO), Poly 3,3bis-azidomethyl oxetane (PolyBAMO) and Copolymer PolyBAMO/AMMO (by TDI end capping) have been synthesized and characterized by different techniques. The appropriate characterization of these energetic polymers is the key point for selecting the best thermoplastic elastomer for propellant applications and also to verify the effects of its structure on the propellant properties, comparable to ordinary binders.

cm of space. Solid samples were analyzed in KBr pellets (0.8:400mg). GPC (Gel Permeation Chromatography was conducted on a Water's gel permeation chromatography equipped with four ultrastyragel columns (100 Å, 500 Å, 1000 Å and 10000 Å), a refractive index detector and a Datamodule 730. THF was used as the mobile phase. It was calibrated with a set of well characterized (i.e., Mn, Mw are well known) polystyrene and polypropylene standards (Narrow Standards), and thus the number average molecular weight (Mn) and weight average molecular weight (Mw) are reported relative to polystyrene and polypropylene. The solvents were purchased from Aldrich, Fluka or Merck according to the purity required, price and availability. Butanediol was purified by distillation prior to use. Synthesis of polymers and copolymers was performed according to the literature (Kawamoto et al., 2005, Kawamoto et al., 2006) and was fully characterized as it has also been the object of other studies at our laboratory (Oliveira et al., 2006, Oliveira et al., 2007). The synthesis of polyAMMO, polyBAMO and of the copolymer polyBAMO/AMMO were performed in accordance to a previous paper (Kawamoto et al., 2006). The ABA-type copolymer was synthesized by using 2,4toluene diisocyanate (TDI) as chain extender, with polyAMMO as soft block and polyBAMO as hard block. The molecular weight (MW) of PolyAmmo, PolyBamo and their copolymer PolyAmmo/Bamo was performed by means of infrared spectroscopy (IR). This method was developed at the Chemistry Division (IAE/Brazil) as an alternative for the determination of the number average molecular weight of polyAMMO, polyBAMO and their copolymer polyAMMO/BAMO. The measurement is based on the azide absorption (FT-IR) band at 2100 cm-1, having as reference the MW determined by NMR analysis of a certain azide polymer. However, as the NMR technique did not work for the copolymers, due to the overlapping of the bands of both polymer segments, the MW of the copolymers was measured by GPC. The band intensity plotted versus the inverse of MW provides a fitting of type Y= a + bX, enabling a simple way of measuring the MW of these kind of polymers.

RESULTS AND DISCUSSION EXPERIMENTAL 1

H-NMR, 13C-NMR analysis were conducted using a 300 MHz Bruker MSL-300 spectrometer. The proton and carbon chemical shifts are recorded in ppm and calibrated on the solvents as internal standard. Infrared spectroscopy was recorded by a Spectrum 2000 PERKINELMER FT-IR spectrometer, in the spectral region of 6500 to 250 cm-1, gain 1, resolution of 4 cm-1 and 40 scans. Liquid samples were analyzed as liquid film in CsI cells separated in 0.025 Journal of Aerospace Technology and Management

PolyBAMO (Fig. 1) and PolyAMMO (Fig. 1) were synthesized by cationic polymerization and the copolymers PolyAMMO/BAMO (Fig. 1) were synthesized by TDI endcapping. AMMO was polymerized using butane diol (BDO) as initiator, and BAMO with benzyl alcohol (BA). The molecular weights of the products were measured by GPC (standard Poly-Styrene) and by 1 H-NMR spectroscopy. At the NMR method the molecular weights were calculated from the correlation between integrals of BDO protons and -CH2N3-, -CH2O- or CH3-groups. V. 1, n. 1, Jan. - Jun. 2009

Synthesis and characterization of energetic thermoplastic elastomers for propellant formulations N ³

concentration, the lower the number of growing chains that consumes the added monomer, leading to a higher molecular weight. 1H-NMR of polyAMMO exhibited three major peaks. At = 3.32 ppm the singlet related to the methylene protons of azidomethyl groups, the splitting at 3.24 ppm refers to CH2O protons of the backbone, and the singlet at 0.98 ppm to the protons of the methyl groups. The small multiplet peak at 1.68-1.69 ppm belongs to the protons of butanediol. The integrals of methylene protons from butane diol and the methyl groups were used for calculating the molecular weights.

H O CH ²

O N ³

Poly AMMO

N ³

H O

N ³

H m

Poly BAMO

CH ²

N ³ O O N ³

Poly BAMO

O C

O N

n H

C N H

N ³ O

N ³ O n

O n

C O

Poly AMMO

O C O

N ³

N ³ O HC ² n

Poly BAMO

Figure 1: Structures of PolyAMMO, PolyBAMO and Poly AMMO/BAMO.

PolyBAMO is a yellow solid with the melting point between 65 to 75°C. The molecular weight calculated from NMR spectra was based on the integrals of BA-ring protons and BAMO-azidomethyl protons. 1H-NMR of polyBAMO exhibited two major peaks close to one another, corresponding to the methylene protons of the azidomethyl group (δ = 3.33ppm) and to the methylene groups of the backbone (δ = 3.32 ppm). The aromatic protons of benzyl alcohol give a multiplett at 7.26-7.37 ppm. The infrared spectrum of polyBAMO shows the opening of the oxetane ring with the formation of the C-O bond, leading to the disappearance of the band related to the oxetane ring at 980 cm-1 (ring stretching) and the appearance of new bands related to the formation of C-O (1000-1100 cm-1) and OH (3400 cm-1), the latter at the end of the polymeric chain. The dominating band is the azide group at around 2110 cm-1. The DSC analysis of all poly BAMO showed the endothermic melting peaks (Tab. 1) and exothermic decomposition peaks with onset temperatures at around 246C, which is typical for organic azide compounds. PolyAMMO is a highly viscous to waxy material depending on the molecular weight. Because polyAMMO is the soft block in the E-TPEs and is located mostly at the centers of the thermoplastic polymer sequences, it was synthesized only as di-functional. This difunctionality allows the later chain elongation on both ends of the molecule. The molecular weight is mainly influenced by the monomer/initiator ratio. The lower the initiator Journal of Aerospace Technology and Management

The FT-IR analysis of polyAMMO showed that polymerization of the corresponding monomer leads to a broadening of most of the vibration modes. The C-O-C stretch of the oxetane ring at 980 cm-1 is replaced by an intense absorption at 1111 cm-1 which refers to C-O-C stretch of the polymer. The OH stretch (broad band around 3300 cm-1) is also present, which is attributed to the end group of the polymer chain. The azide group appears at approximately 2100 cm-1 and does not have a significant change in comparison to AMMO spectrum. The DSC analysis of polyAMMO shows only an exothermic peak from decomposition of the azide groups at the expected onset temperature around 256C. The 1H-NMR analysis of the copolymer showed the main peaks of the corresponding polymers (polyAMMO and polyBAMO) and also from TDI (small peaks). From polyAMMO peaks were observed at 0.92 ppm (singlet) corresponding to the CH3 protons, a multiplet at 3.16 3.21 ppm of the CH2O protons of the chain backbone and another singlet at 3.24 ppm of the methylene protons of athe zidomethyl groups. From polyBAMO at 3.30-3.32 a broad singlet can be observed that corresponds to 4H of -CH2Oand 4H of -CH2N3. The small multiplet peak at 1.55-162 ppm belongs to the protons of butanediol and at 2.13 and 2.19 singlets of the 3H of -CH3 can be observed from the TDI isomers. The FT-IR spectra of polyAMMO/BAMO showed that the addition reaction was quantitative because of the absence of the isocyanate band at 1700 cm-1. The strongest band is caused by the azido groups at 2106 cm-1 and from the C-O-C stretch vibration of the polymer backbone (1102 cm-1). A broad band at 3364 cm-1 comes from the N-H-vibration of the urethane groups. The DSC analysis of the copolymer shows an endothermic melting peak at 74 °C and an exothermic peak at 248 C. For the starting polymers polyBAMO and polyAMMO, the exothermic peaks are at 246 C and 256 C, respectively. It is seen that the decomposition peak temperature of the copolymer is very close to that of polyBAMO, indicating that AMMO units do not significantly affect the thermal decomposition of the copolymer. Therefore, the thermochemical characteristics of the copolymer polyBAMO/AMMO are similar to polyBAMO. V. 1, n. 1, Jan. - Jun. 2009

Kawamoto, A.M. et al.

Table 1 shows the molecular weight values of polyAMMO, polyBAMO and of copolymer polyAMMO/BAMO, measured by NMR and GPC, together with the absorbance of the azide group at 2100 cm-1. This refers to the N3 group that was measured to use the measuring method of the molecular weight (Mw) of polyAMMO, polyBAMO and their copolymer polyAMMO/BAMO by means of infrared spectroscopy (IR).

9779 AK 80 Poly AMMO 6350 AK 96 Poly AMMO 15875 AK 113 Poly AMMO 4200 AK 97 Poly BAMO 4368 AK 81 Poly BAMO 9744 AK 110 Poly BAMO 4872 AK 116 Poly BAMO 1680 AK 133 Poly BAMO AK 98 Poly AMMO/BAMO AK 109 Poly AMMO/BAMO AK 120 Poly AMMO/BAMO

IR Mw by absorbance (azide GPC group) 5358 2332 3076

2.626 2.773 2.354 2.693 2.623 2.260 3.116 5.927 2.604 2.513 2.405

The molecular weight of the aforementioned polyBAMO was calculated by correlating the NMR spectra integrals of benzyl alcohol (BA)-ring protons and BAMO-azidomethyl protons. The molecular weight of polyAMMO was calculated by correlating the NMR spectra integrals of butanediol (BDO) protons and -CH2N3-, -CH2O- or CH3groups. The Mw of the copolymer was measured by GPC. With these results it was possible to build four curves that relate the intensity of the IR band of the azide group with the inverse of molecular weight of PolyAMMO (Fig. 2), Poly BAMO (Fig. 3), PolyAMMO/BAMO (Fig. 4) and all of them together in only one curve (Fig. 5).

6,0

Poly-AMMO 5,5 5,0 4,5

Abs[N ] 続

Mw by NMR

Y = 2.11 + 2403.459 X Where: Y = medium value of N3 absorbance (A2100) X = inverse of molecular weight for PolyAMMO

Table 1: Properties of polymers and copolymers.

Polymers/Copolymers

The relationship between the azide band intensity and the inverse of molecular weight for PolyAMMO shown in Fig. 2 enabled to observe a linear tendency relationship with a coefficient of 0.997, which can be represented by the following equation:

4,0 3,5

Y = 0.78 - 6832.362 X

3,0 3,5 2,0 0,0001

0,0002

0,0003

0,0004

0,0005

0,0006

1 / M W [g/mol]

Figure 3: Intensity of azide band vs. inverse of molecular weight for PolyBAMO.

The relationship between the azide band intensity and the inverse of molecular weight for PolyBAMO shown in Fig. 3 enabled to observe a linear relation with a coefficient of 0.981. A good linear relationship was obtained (R= 0.981) and it is represented by the following equation: Y = 0.78 - 6832.362 X Where: Y = medium value of N3 absorbance (A2100) X = inverse of molecular weight for PolyBAMO

Poly-AMMO/BAMO

2,60

Abs[N ] 続

2,55

2,8

Y = 2.177 + 1794.199X 2,45

Poly-AMMO

2,7

Abs[N ] 続

2,50

2,40

0,00012

2,6

0,00014

0,00016

0,00018

0,00020

0,00022

0,00024

1 / M W [g/mol] Y = 2 . 11 + 2 4 0 3 . 4 5 9 X

2,5

Figure 4: Intensity of azide band vs. inverse of molecular weight for PolyAMMO/BAMO.

2,4

2,3 0,00004

0,00008

0,00012

0,00016

0,00020

0,00024

1 / M W [g/mol]

Figure 2: Intensity of azide band vs. inverse of molecular weight for PolyAMMO. Journal of Aerospace Technology and Management

The relationship between the azide band intensity and the inverse of molecular weight for PolyAMMO/BAMO shown in Fig. 4 enabled to observe a linear tendency relationship with a coefficient of 0.996 which can be V. 1, n. 1, Jan. - Jun. 2009

Synthesis and characterization of energetic thermoplastic elastomers for propellant formulations

represented by the following equation: Y = 2.177 + 1794.199 X Where: Y = medium value of N3 absorbance (A2100) X= inverse of molecular weight for PolyAMMO/BAMO

The curves suggest that the methodology developed in our laboratory and described herein are very useful as a practical and fast alternative to determine a molecular weight of a known polymer that needs to be synthesized routinely and also for scaling up purposes.

Poly-AMMO Poly-BAMO Poly (BAMO/AMMO)

6,0 5,5

and the IR absorbance of N3 band intensity of PolyAMMO, Poly BAMO and Poly AMMO/BAMO have been measured and the curves of the N3 band intensity were plotted vs. the inverse of MW, hence providing a type Y= a + bX curve, which will allow a simple analysis of the same type of MW polymer/copolymer.

5,0

Abs[N ] ³

4,5

REFERENCES

4,0 3,5 3,0 3,5 2,0 0,0000

0,0001

0,0002

0,0003

0,0004

0,0005

0,0006

1 / M M [g/mol]

Figure 5: Intensity of azide band vs. inverse of molecular weight for PolAMMO, PolyBAMO and PolyAMMO/BAMO.

The relationship between the azide band intensity and the inverse of molecular weight for PolyAMMO, PolyBAMO and PolyAMMO/BAMO shown in Fig. 5 also enabled to observe a linear relationship with a coefficient of 0.950. A good linear relation was obtained (R= 0.950) and it is represented by the following equation: Y = 1.388 + 7041.963 X Where: Y = medium value of N3 absorbance (A2100) X= inverse of molecular weight for PolyAMMO/BAMO The linear relationship in this case is not very precise as it is for single compounds, given that the points in the curves are not precisely distributed and also a curve could fit to join the points. Therefore the method for predicting a molecular weight from the intensity of azide band of the polymers or copolymers is better estimated using curves for only a specific compound.

CONCLUSION PolyAMMO and polyBAMO has been successfully synthesized by cationic polymerization, and the thermoplastic elastomers (TPEs) were synthesized using the chain elongation method of PolyAMMO, GAP and PolyBAMO by diisocyanates. 2.4-Toluene diisocyanate (TDI) was used to link block A (hard and mono-functional)) to B (soft and di-functional). For the hard A-block we used PolyBAMO and for soft B-block we used PolyAMMO or GAP. This copolymer will be included in future research program to be tested in formulations of solid rocket propellants. The molecular weight measurements by GPC and NMR Journal of Aerospace Technology and Management

Archibald, T. G., Carlson, R. P., Malik, A. A., Manser, G. E., 1997, “Preparation and Polymerization of Initiators Containing Multiple Oxetane Rings: New Routes for Star Polymers”, US Patent 5,663,289. Hsiue G. H., Liu Y. L. and Chiu Y. S., 1994, “Triblock Copolymers Based on Cyclic Ethers: Preparation and Properties of Tetrahydrofuran and 3,3-bis (Azidomethyl) Oxetanetriblock Copolymers”, Journal of Polymer Science, Part A: Polymer Chemistry, Vol. 32, pp. 21552159. Kawamoto A. M. et al., 2005, “Synthesis and Characterization of Energetic Oxetane-Oxirane-Polymers for use in Thermoplastic Elastomer Binder Systems”, Proceedings of the 36th International Annual Conference &32th International Pyrotechnics Seminar of ICT, Karlshure, Germany. Kawamoto A. M., et al., 2006, “Synthesis and Characterization of Energetic ABA-Type Thermoplastic Elastomers for Propellants Formulations”, Proceedings of the 37th International Annual Conference of ICT, Karlshure, Germany. Manser, G. E., Miller, R. S., 1993, “Thermoplastic Elastomers Having Alternate Crystalline Structure For Us as High Energy Binders”, US Patent 5,210,153. Manser, G. E., Malik, A. A., Archibald, T. G., 1996, “3Azídation-3-Nitratomethyloxetane”, US Patent 5,489. Murali M. Y., Padmanabha R. M., and Mohana R. K., 2004, “Synthesis, Spectral and DSC Analysis of Glycidyl Azide Polymers Containing Different Initiating Diol Unit”, Journal of Applied Polymer Science, Vol. 93, pp. 21572163. Oliveira, J. I. S., et al., 2006, “Characterization MIR/NIR/FIR of Energetic Binders used in Solid Propellants”, Propellants, Explosives, Pyrotechnics, Vol. 32, pp. 395. V. 1, n. 1, Jan. - Jun. 2009

Kawamoto, A.M. et al.

Oliveira, J. I. S., et al., 2007, “Determination of CHN Content in Energetic Binder by MIR Analysis”, Polímeros: Ciência e Tecnologia, Vol. 17, pp. 46. Provatas, A., “Energetic Polymers and Plasticizers for Explosive Formulations-A Review of Recent Advances”, Defense Science & Technologie Organization, DSTO-TR0966. Saegusa T., Matsumoto S., and Hashimoto Y., 1970, “Cationic Block Copolymerization of Tetrahydrofuran with 3,3-Bis(Chloromethyl) Oxacyclobutane”, Macromolecules, Vol. 3, pp. 377. Sanderson, A. J., Edwards, W., 2000, “Method for the Synthesis of Energetic Thermoplastic Elastomers in InonHalogenated Solvents”, WO 00/34353, (PCT)/US99/24013”. “Synthesis of energetic thermoplastic elastomers containing oligomeric urethane linkages”, 2000, WO 00/34350 A3 (PCT). Wardle, R. B., Edwards, W. W., Hinshaw, J. C., 1996, “Method of Producing Thermoplastic Elastomers Having Alternate Crystalline Structure Such as Polyoxetane ABA or Star Block Copolymers by a Block Linking Process”, US Patent 5,516,854. Wardle, R. B., 1989, “Method of Producing Thermoplastic Elastomers Having Alternate Crystalline Structure for Use as Binders in High-Energy Compositions”, US Patent 4.

Journal of Aerospace Technology and Management

V. 1, n. 1, Jan. - Jun. 2009

Ulrich Teipel* Georg-Simon-Ohm University Nuremberg - Germany ulrich.teipel@ohm-hochschule.de

Ulrich Förter-Barth Institut Chemische Technologie Pfinztal - Germany

*author for correspondence

Rheology of suspensions with aluminum nano-particles Abstract: Nano-scale aluminum particles are innovative materials increasingly used in energetic formulations. In this contribution, the rheological behavior of suspensions with either paraffin oil or HTPB as the matrix fluid and nano-scale aluminum (ALEX) as the dispersed phase is described and discussed. The paraffin oil/aluminum suspensions exhibit non-Newtonian flow behavior over a wide range of concentrations, whereas the HTPB/aluminum suspensions exhibit Newtonian behavior (i.e. the viscosity is independent of shear stress) up to a concentration of 50 vol.% aluminum. Both systems have unusual viscoelastic properties in that their elastic moduli are independent of the solids concentration. Key words: Aluminum nano-particles, Rheology, ALEX, HTPB, Viscoelastic properties

LIST OF SYMBOLS .

η(γ) γ γ^ ω τ(t) δ G*(ω) G'(ω) G''(ω) η ρ S

F low properties Deformation Amplitude Radial frequency Sinusoidal shear stress Phase shift Shear modulus Storage modulus Loss modulus Dynamic viscosity of Density Specific surface

At such small sizes, interparticle interactions become significantly more important and, as a result, nano-scale particles have a higher tendency to agglomerate (Glotov, 2000). In addition, the changed material poses difficulties when they are mixed with a fluid polymer matrix. This work examines and discusses the rheological properties of suspensions containing nano-scale aluminum particles in steady state and oscillatory shear flows. EXPERIMENTAL Measurement Methods

INTRODUCTION Aluminum particles are well known as an ingredient in energetic materials. The typical diameter of aluminum used in explosives and propellants is in the order of ~ 30 µm (Miller, 1991). To enhance aluminum reactivity, for instance during combustion of solid rocket propellants, it is advantageous to use particles with the largest possible specific surface area, i.e., particles with a smaller mean particle size are desirable. By vaporizing and subsequently condensing aluminum in argon, or by electric explosion of an aluminum wire, it is possible to produce aluminum particles in the nanometer size range (Ivanov and Tepper 1997, Tepper and Ivanov 1998). Particles in this size range exhibit physical properties very different than those in the micrometer range. At such small sizes, interparticle interactions become significantly more important and, as a result, nano-scale particles have a higher tendency to agglomerate (Glotov, 2000). ____________________________________ Received: 30/04/09 Accepted: 04/05/09

Journal of Aerospace Technology and Management

The rheological behavior of suspensions filled with nanoscale aluminum was examined in steady state and oscillatory shear flow using a UDS 200 rotational rheometer manufactured by Physica Meßtechnik GmbH. The measurement fixtures included a modified coaxial cylinder (Mooney-Ewart-System) and a cone and plate. Under steady state shear flow, the characteristic material function can be described as follows: (1) .

Here, η(γ) is a characteristic material function that describes the flow properties when the fluid is subjected to a rheometric flow. In oscillatory shear flow, the fluid is subjected to a periodic (e.g., sinusoidal) deformation γ(t) with an amplitude γ^ at a radial frequency ω = 2πf (Fig. 1) (Teipel, 1999): (2) Subjecting the material to an oscillatory (sinusoidal) shear deformation at sufficiently small amplitudes, i.e. in the linear viscoelastic range, results in a sinusoidal shear stress V. 1, n. 1, Jan. - Jun. 2009

Teipel, U., Förter-Barth, U.

τ(t) output (Fig. 2). Viscoelastic material behavior is characterized by the existence of a phase shift δ between the shear stress output τ(t) and the deformation input γ(t): (3) By definition, the phase shift of a perfectly elastic solid is zero and that of a purely viscous fluid is π/2, whereas for viscoelastic fluids it is 0<δ<π/2. The shear stress function can be described in terms of the frequency dependent complex shear modulus G*(ω),

linear viscoelastic region, the moduli G'(ω), G''(ω) and G*(ω) are independent of the oscillatory amplitude in tests conducted at a constant frequency. The mean particle size and particle size distribution of the aluminum were determined via laser diffraction spectrometry or photon correlation spectroscopy. Scanning electron micrographs were accomplished to further characterize the material.

(4) The complex shear modulus can also be expressed as (5) The complex shear modulus G*(ω) of a viscoelastic material is composed of two material functions, a real and an imaginary component, called the storage modulus, G'(ω), and the loss modulus, G''(ω), respectively. The storage modulus G'(ω) is proportional to the deformation energy stored by the material (the elastic component), while the loss modulus G''(ω) is proportional to the amount of energy dissipated by the material (the viscous component). (6)

γ, γ γ^

Figure 2: Shear stress profile of a viscoelastic fluid resulting from an oscillatory shear deformation.

Materials The suspensions investigated consisted of nano-scale aluminum particles dispersed in paraffin oil or hydroxylterminated polybutadiene (HTPB). The paraffin oil exhibited Newtonian flow behavior with a dynamic viscosity of η(20 °C) = 198 mPas. It had a ρ = 874.7 kg/m3 density and a σ = 30.5 mN/m surface tension. The hydroxyterminated polybutadiene (designated HTPB R 45-M) also exhibited Newtonian flow behavior with a dynamic viscosity of η(20 °C) = 9300 mPas. The nano-scale aluminum (ALEX) was obtained from Argonide Corporation, Stanford, Florida/USA. The density of the aluminum particles was determined by gas pycnometry to be ρ = 2.4 g/m3 and the specific surface area determined by gas adsorption was S = 11.2 m2/g. A SEM image of the aluminum powder is shown in Fig. 3

γ Figure 1: Deformation and shear rate profiles in oscillatory shear flow.

Oscillatory shear experiments must be conducted at deformations within the material's linear viscoelastic range. In this range, at a constant radial frequency , the deformation amplitude γ^ is proportional to the resulting shear stress amplitude τ^ , i.e., τ^ ~γ^ : This is only the case for sufficiently small oscillatory deformations. Within the Journal of Aerospace Technology and Management

Figure 3: Nano-scale aluminum powder. V. 1, n. 1, Jan. - Jun. 2009

Rheology of suspensions with aluminum nano-particles

Flow Behavior of the Paraffin Oil/Aluminum Suspensions Prior to the rheological characterization, the paraffin oil/ aluminum suspensions were stirred for a number of hours and the aluminum was well dispersed using an ultrasound homogenizer. This process ensured that aluminum agglomerates were broken down and the suspension was adequately homogenized. After mixing, the flow behavior was characterized under steady shear flow. Fig. 4 illustrates the relative viscosity as a function of shear rate for the suspensions, which ranged in solids concentration from 2 to 45 vol.%, as well as for the pure paraffin oil. 10000

Cv=0 vol%

viscosity is much less pronounced at higher shear rates because of the flow induced structuring of the system. Figure 5 shows the relative viscosity of the suspension as a function of solids concentration for the limiting viscosity at . . zero shear rate ( γ → 0) and at a relatively high shear rate, γ = -1 1000 s . 10 pure HTPB Cv=2,48 vol% Cv=4,81 vol%

Relative viscosity

RESULTS

Cv=11,21 vol% Cv=20,16 vol% Cv=24 vol% Cv=27,48 vol% Cv=38,7 vol% Cv=46,92 vol%

Cv=2,67 vol% Cv=5,2 vol%

1000 Relative viscosity

Cv=12,06 vol%

1 0,001

0,01

0,1

1 . 10 Shear rate γ [1/s]

100

1000

Cv=21,53 vol%

100

Cv=25,53 vol% Cv=29,15 vol% Cv=32,43 vol%

Cv=35,43 vol% Cv=38,15 vol%

Cv=40,68 vol% Cv=43 vol% Cv=45,14 vol%

0,1 0,001

Figure 5: Relative viscosity of paraffin oil/aluminum suspensions as a function of solids concentration.

0,01

0,1

100

1000 10000

Shear rate γ [1/s]

Figure 4: Relative viscosity of the paraffin oil/aluminum suspensions as a function of shear rate; = 20 °C.

The relative viscosity rel is defined as the ratio of the viscosity of the suspension to that of the matrix fluid at a . constant shear rate γ :

(7) With increasing aluminum concentration the suspensions exhibit more and more distinct shear thinning behavior. This non-Newtonian response can be attributed to particleparticle interactions and the changed hydrodynamics of the suspension compared to the single phase fluid. At small shear rates, the viscosity increase as a function of concentration is particularly pronounced. In this shear rate range, the interparticle forces dominate the relatively weak hydrodynamic forces, so that the rheological response of the suspension is strongly dependent on the solids concentration and the resulting structural interactions. As the shear rate is increased, the hydrodynamic forces also increase, leading to flow induced structuring of the nano-scale particles and a corresponding decrease in the viscosity at a given solids concentration. The effect of solids concentration on the suspension Journal of Aerospace Technology and Management

At the highest shear rate examined, a linear increase in the relative viscosity as a function of solids concentration is observed, up to a CV ~~ 25 vol.% concentration. At very low concentrations, there is almost no difference in the relative viscosity determined at the minimum and maximum shear rate. In this range of concentration, sufficient distance between the particles contributes to small particleparticle interactions, and likewise flow induced orientation of the particles has a relatively minor effect on the viscosity. Increasing the concentration leads to an increased contribution of the viscosity from particleparticle interactions. The quiescent particle structure formed with increasing concentration at low shear rates is one of the reasons for the strong concentration dependence of the limiting viscosity at zero shear rate, as shown in Fig. 5. At higher shear rates a flow induced structure is formed leading to a reduction in the relative viscosity at a given solids concentration. The difference of the viscosity . . function at the two shear rates γ → 0 and γ = 1000 s-1, which increases with increasing solids concentration, can be attributed primarily to the behavior of the particles in the Couette flow. At a concentration of 45 vol.%, the viscosity difference is nearly of the order of 104.

Flow Behavior of HTPB/Aluminum Suspensions Figure 6 shows the relative viscosity of the HTPB/aluminum suspensions as a function of shear rate for solids concentrations from 0 < CV < 47 vol.%. Hydroxyterminated polybutadiene, HTPB R 45-M, without additives exhibits Newtonian flow behavior, see Fig. 6 (Hordijk, 1996 and Muthiah, 1996). V. 1, n. 1, Jan. - Jun. 2009

Teipel, U., Förter-Barth, U. 10000

Viscoelastic Properties of the Suspensions

Relative viscosity

1000

. η(γ

100

. η(γ = 1000s ¹)

Viscoelastic material properties can be determined by oscillatory shear experiments. The complex shear modulus determined by dynamic experiments in the linear viscoelastic region can be expressed in terms of two material functions (as shown in Eq. (6)), the storage modulus G'(ω) and the loss modulus G''(ω). The storage and loss modulus functions of the paraffin oil/aluminum suspensions are shown in Fig. 8 for various solids concentrations.

1 10

Solids concentration, by volume, cv [vol%]

1000

G’ Cv=21,53 vol% G’ Cv=25,53 vol%

Figure 6: Relative viscosity of HTPB/aluminum suspensions as a function of shear rate, = 20°C.

In contrast to the paraffin oil/aluminum suspensions, the HTPB suspensions exhibited Newtonian behavior over a wide shear rate range up to a solids concentration of ~ 50 vol.%. With increasing concentration, the relative viscosity of the suspensions increased; however, the behavior remained linear. Figure 7 shows the relative viscosity of the suspensions as a function of solids concentration.

G’ Cv=29,15 vol%

100

G’ Cv=32,43 vol% G’ Cv=35,43 vol%

G’/g’’ [Pa]

G’ Cv=38,17 vol%

G’ Cv=40,68 vol% G’ Cv=21,53 vol%

G’ Cv=25,53 vol% G’ Cv=29,15 vol% G’ Cv=32,43 vol%

0,1

G’ Cv=35,43 vol% G’ Cv=38,17 vol%

0,01

G’ Cv=40,68 vol%

0,1

100

1000

Frequency ω [1/s]

Figure 8: Storage and loss modulus functions of the paraffin oil/aluminum suspensions.

Relative viscosity

1 0

Solid volume concentration cv [vol%]

At low frequencies the storage modulus is smaller than the loss modulus, meaning that the viscous properties are dominant in this frequency range. Both functions increase steadily with frequency; however, the slope of the storage modulus function is greater than that of the loss modulus and, as a result, the two functions intersect at a characteristic frequency ωi, which differs depending on the solid volume concentration. Above this frequency, the elastic properties are dominant. The structural relaxation time λ is equal to the reciprocal of the frequency at which the storage and loss moduli intersect: (9)

Figure 7: Relative viscosity of the HTPB/aluminum suspensions as a function of solids concentration.

The rheological characterization of the HTPB-based suspensions filled with nano-scale aluminum yielded the following relationship for the relative viscosity as a function of solid volume concentration:

(8) Eq. (8) is valid for solid volume concentrations CV up to 50 vol.%. Journal of Aerospace Technology and Management

For the paraffin oil/aluminum suspensions up to solids concentrations CV < %40 vol.%, the structural relaxation time range is from 0.24 s < λ 0.37 s. It was also observed that the storage modulus G'(ω) was essentially independent of the aluminum concentration. One concludes that for these suspensions, filled with nano-scale particles, the stored (elastic) deformation energy is independent of the particle concentration. The storage and loss modulus functions of the HTPB/aluminum suspensions are shown in Figure 9 for various solids concentrations. As in the previous case, the storage modulus G'(ω) is independent of solids concentration. However, the structural relaxation times for V. 1, n. 1, Jan. - Jun. 2009

Rheology of suspensions with aluminum nano-particles

the HTPB-based suspensions are significantly smaller than those of the paraffin oil-based suspensions, falling in the millisecond range (0.0021 s < λ < 0.0062 s) 10000

G’; Cv=11,21 vol% G’’; Cv=11,21 vol% G’; Cv=20,16 vol%

1000

Generalized Correlation and Evaluation of Pot Life'', Propellants, Explosives, Pyrotechnics, Vol. 21, pp.186-192. Teipel,U., 1999, ''Rheologisches Verhalten von Emulsionen und Tensidlösungen'', Dissertation, Universität Bayreuth; Wissenschaftliche Schriftenreihe des Fraunhofer ICT, Band 22.

G’’; Cv=20,16 vol%

G’/g’’ [Pa]

G’; Cv=24 vol%

100

G’’; Cv=24 vol% G’; Cv=27,48 vol% G’’; Cv=27,48 vol%

G’; Cv=38,7 vol%

Tepper, F., Ivanov,G. V., Lerner, M. and Davidovich, V., 1998, ''Energetic Formulations from Nanosize Metal Powders'', 24th International Pyrotechnics Seminar, Monterey, California, USA, July 2731, pp. 519-530.

G’’; Cv=38,7 vol% G’; Cv=43,11 vol%

G’’; Cv=43,11 vol% G’; Cv=46,92 vol%

0,1 0,1

G’’; Cv=46,92 vol%

100

1000

10000

Frequency ω [1/s]

Figure 9: Storage and loss modulus functions of the HTPB/aluminum suspensions.

CONCLUSION The paraffin oil/aluminum suspensions exhibit nonNewtonian flow behavior over a wide range of concentrations, whereas the HTPB/aluminum suspensions exhibit Newtonian behavior (i.e. the viscosity is independent of shear stress) up to a concentration of 50 vol.% aluminum. Both systems have unusual viscoelastic properties in that their elastic moduli are independent of the solids concentration.

REFERENCES Glotov, O. G., Zarko, V. E, and Beckstead, M. W. , 2000 ''Agglomerate and Oxide Particles Generated in Combustion of Alex Containing Solid Propellants'', 31st International Annual Conference of ICT, Karlsruhe, Germany, June 2730, pp. 130/1130/15. Hordijk, A. C., Sabel,H. W., Schonewille, R. L. and Meulenbrugge, J. J., 1996, ''The Application of Rheological Equipment for Improved Processing of HTPB based PBXs'', 27th International Annual Conference of ICT, Karlsruhe, Germany, June 2528, pp. 3/13/11. Ivanov, G. V. and Tepper, F., 1997, ''Activated Aluminum as a Stored Energy Source for Propellants", in: K. K. Kuo (ed.) ''Challenges in Propellants and Combustion, 100 Years after Nobel'', Begell House, pp. 636-645. Miller, R. R., Lee, E. and Powell, R. L., 1991, ''Rheology of Solid Propellant Dispersions'', Journal of Rheology , Vol.35, No. 5, pp.901-920. Muthiah, R, Krishnamurthy, V. N. and Gupta, B. R., 1996,''Rheology of HTPB Propellant: Development of Journal of Aerospace Technology and Management

V. 1, n. 1, Jan. - Jun. 2009

Vanderlei O. Gonçalves* Instituto de Aeronáutica e Espaço São José dos Campos - Brasil vanderlei@iae.cta.br

Luiz Cláudio Pardini Instituto de Aeronáutica e Espaço São José dos Campos - Brasil pardini@iae.cta.br

Kledermon Garcia Instituto de Aeronáutica e Espaço São José dos Campos - Brasil kleder@iae.cta.br

Antonio Carlos Ancelotti Jr Instituto Tecnológico de Aeronáutica São José dos Campos - Brasil antonio.ancelotti@embraer.com.br

Eduardo Marcelo Bezerra Instituto Tecnológico de Aeronáutica São José dos Campos - Brasil edumarcelo@superig.com.br

* autor para correspondência

Resistência ao cisalhamento Iosipescu em compósitos de fibra de carbono e de vidro com resina epóxi Resumo: O principal objetivo do presente trabalho foi a determinação do módulo de cisalhamento G12 e a máxima resistência ao cisalhamento (ô12) utilizando o ensaio de cisalhamento Iosipescu. Os testes foram conduzidos com dois tipos de compósitos, fibra de carbono/epóxi e fibra de vidro/epóxi utilizados na indústria aeroespacial e também uma matriz de resina moldada. Os resultados indicam a efetiva contribuição das fibras de reforço para a resistência ao cisalhamento (ô12) e para o módulo de cisalhamento (G12) comparado com a matriz polimérica sem reforço. Palavras-chave: Compósitos, Fibra de carbono, Fibra de vidro, Cisalhamento Iosipescu, Resina epóxi.

Iosipesco shear resistance in composites of carbon and glass fiber with epoxi resin Abstract: The main aim of the present work was the determination of the shear modulus (G12 ) and the maximum shear strength (ô12) using the Iosipescu Shear Test. Tests were carried out on two types of composites, carbon fiber/epoxy and glass fiber/epoxy, used in the aerospace industry, and also a molded epoxy resin matrix. The results indicate the effective contribution of fiber reinforcements to the shear strength (ô12) and shear modulus (G12) compared to the no reinforcement polymer matrix. Key Words: Composites, Carbon fiber, Glass fiber, Iosipescu shear, Epoxy resin.

LISTA DE SÍMBOLOS cdp G G12 P τ12 ε γ Pa Gpa Mpa µm/m

Corpo de Prova Módulo de cisalhamento Módulo de cisalhamento no plano Carga aplicada no dispositivo de ensaio Tensão de cisalhamento no plano Deformação específica longitudinal Deformação específica angular Pascal = 1 Newton /m2 Giga Pascal = 1 Pa x 109 Mega Pascal = 1 Pa x 106 Micro-metro por metro = 1 m x 10-6

INTRODUÇÃO Os materiais compósitos formados de fibra de carbono/epóxi e de fibra de vidro/epóxi têm estabelecido seu uso na indústria aeroespacial. Tipicamente, a manufatura desses materiais é realizada pelo empilhamento de camadas de fibras de reforço. Assim, a resistência mecânica paralela ao plano das fibras atende aplicações de uso aeroespacial que se alia ao fato do material possuir ___________________________________ Recebido: 30/04/09 Aceito: 13/05/09 Journal of Aerospace Technology and Management

baixa massa específica. Entretanto, o empilhamento de camadas implica na existência de umaregião interlaminar ocupada essencialmente por resina que apresenta uma resistência, no caso de cisalhamento, dez vezes menor que a resistência no plano de reforço. A medida da resistência ao cisalhamento de compósitos envolve desafios, tendo em vista o fato de que é necessário induzir um estado de tensões cisalhantes no plano. Assim, dentre as propriedades semi-estáticas, como a resistência à tração e à compressão, a resistência ao cisalhamento em compósitos estruturais é provavelmente uma das mais difíceis de serem determinadas com confiabilidade. Há vários métodos para avaliar a resistência ao cisalhamento no plano em compósitos. Exemplos de ensaios utilizados para operacionalizar essas medidas são o cisalhamento Iosipescu, tração 10º fora-de-eixo, tração [+45º/-45º1]ns, cisalhamento em 2 trilhos, cisalhamento em 3 trilhos, torção em cilindros sólidos e torção em tubos de parede fina e resistência ao cisalhamento interlaminar (Pindera, 1989, Odegard, 2000, Khashaba , 2004, Hussain, 1999, Lessard, 1995, Ferry, 1999 e El-Assal, 2007). Recentemente, o teste Arcan, oriundo de ensaio de cisalhamento para madeira, também tem sido empregado para avaliação de resistência ao cisalhamento de compósitos (Hung, 1997). V. 1, n. 1, Jan. - Jun. 2009

Gonçalves, V. O. et al.

Em alguns desses testes de cisalhamento os resultados apresentam inconsistências devido ao fato do estado de tensão de cisalhamento na seção dos corpos de prova não serem puros e, na maioria dos casos, também não serem uniformes. Por sua vez, o ensaio de cisalhamento Iosipescu tem sido o mais utilizado atualmente para determinar as propriedades de cisalhamento em compósitos. O ensaio de cisalhamento Iosipescu, representado na Fig. 1, foi proposto originalmente no início dos anos 60 para materiais isotrópicos, e posteriormente adaptado para uso em compósitos desde o início da década de 1970 (Walrath, 1983).

Figura 1: Esquema do dispositivo de ensaio (ASTM Designation: D 5379/D 5379M 05).

No ensaio de cisalhamento Iosipescu, a presença do entalhe em V, como mostra a Fig. 2, resulta em um estado de tensão na seção do entalhe que pode ser considerado puro mesmo que ainda não uniforme (Pindera, 1989, Tew, 2001). Existem seis possibilidades possíveis de medidas de resistência ao cisalhamento em função da orientação das fibras no plano, conforme mostrado na Fig. 3.

Figura 3: Seis orientações possíveis para as tensões e módulo. ASTM D 5379M/05).

Os módulos de cisalhamento G e as tensões de cisalhamento τ obtidos neste trabalho são relativos à direção no plano, ou seja, G12 e τ12. O módulo de cisalhamento no plano G12 é obtido através do gráfico τ versus γ, tensão de cisalhamento pela deformação angular e o coeficiente angular da reta na zona elástica deste gráfico será o G12, conforme mostrado na Fig. 4.

Figura 2: Diagrama de corpo livre com os diagramas de cisalhamento e de momento fletor. (ASTM D 5379M/05). Journal of Aerospace Technology and Management

Figura 4: Esquema do gráfico τ x γ para obtenção do módulo G12. V. 1, n. 1, Jan. - Jun. 2009

Resistência ao cisalhamento Iosipescu em compósitos de fibra de carbono e de vidro com resina epóxi

Para a região linear mostrada na Fig. 4 é válida a lei de Hooke obtendo-se assim o módulo G12 conforme Eq. (1). τ = Gγ

(1)

A Figura 5 mostra que quando a carga P1 é aplicada existe a tendência de ocorrer uma rotação em uma região parcial da amostra, mas devido à configuração do dispositivo ocorre uma reação P2 evitando a rotação da mesma. Portanto, neste ensaio, dois pares de força são aplicados através da seção entre as raízes dos entalhes em V gerando dois momentos contrários produzindo um estado puro e uniforme de tensão de cisalhamento na seção A-B, (Dias, 2004).

Figura 5: Esquema de aplicação de carga do ensaio Iosipescu.

EXPERIMENTAL O cisalhamento na seção entre os entalhes é igual à carga P aplicada no dispositivo de ensaio e não existe flexão nesta região entre os entalhes. Por definição a média da tensão de cisalhamento na seção dos entalhes é demonstrada na Eq.(2). τ = P/(t.w) (2) Onde P é a força aplicada em Newton, t é a espessura do corpo de prova e w é a distância entre a origem dos entalhes. A deformação angular ou de cisalhamento é calculada através de dois extensômetros elétricos colados a ± 45º próximos a origem dos entalhes conforme mostra a Fig. 6.

corpo de prova, ε1 e ε2, e por meio da Eq. (3) é calculada a deformação angular ou de cisalhamento γ. γ

= │ε1│ + │ε2│

(3)

Os materiais utilizados neste trabalho foram: Material #1: Resina epóxi Epon 826 com endurecedor Epicure 527 (26% em massa sobre a resina) e acelerador Epicure W (1% em massa sobre a resina). O ciclo de cura utilizado foi de 1 hora a 80º C, 2 horas a 120º C e 2 horas a 180º C. Material # 2: Compósito de fibra de vidro/resina epóxi, com orientação das fibras de vidro de 0/90º com relação ao eixo horizontal, obtido com 8 camadas e com teor de fibra de vidro de 64±1 %/massa. Foram manufaturados em autoclave, utilizando pré-impregnados de tecido 5HS 7781, da Hexcel Co. Estes compósitos apresentam 55% em volume de fibras. Material # 3: Compósito de fibra de carbono/resina epóxi com orientação das fibras de carbono de ±45º com relação ao eixo horizontal, obtido com 8 camadas e com nível de porosidade menor que 1,5 %. Foram manufaturados em autoclave utilizando pré-impregnados de tecido plano F155, da Hexcel Co. Estes compósitos apresentam 58% em volume de fibras. As resinas utilizadas nos pré-impregnados, material # 2 e # 3, são de formulação proprietária. Embora a formulação da resina utilizada no material #1 não seja a mesma do sistema de resina utilizado nos pré-impregnados, os ensaios foram realizados de forma comparativa para demonstrar tendências no comportamento em fadiga para os diversos materiais testados. Além disso, as resinas epóxi utilizadas em compósitos estruturais, de forma geral, apresentam modo de fratura frágil na ruptura quando submetidas a quaisquer tipos de carregamentos mecânicos (Kinloch, 1995). Foi ensaiado um total de dezesseis corpos de prova, sendo seis de compósito com fibra de carbono, cinco de compósito com fibra de vidro e cinco de resina epóxi. Os ensaios foram realizados no Laboratório de Ensaios Estruturais - ASA-E/IAE. Foi utilizado um equipamento de ensaios marca MTS modelo 810.25 com célula de carga de 25 kN. A aquisição de dados foi realizada em equipamento marca “National Instruments” modelo SCXI e aplicativo computacional “Labview”, para a coleta dos dados de deformação dos extensômetros e da carga aplicada. Os ensaios foram executados de acordo com a norma ASTM 5379M/05 e utilizado um dispositivo padrão conforme mostrado nas Fig. 1 e 7.

Figura 6: Esquema de colagem dos extensômetros elétricos a ± 45º. (ASTM D 5379M/05).

Os extensômetros elétricos medem as deformações longitudinais a ± 45º com relação ao eixo horizontal do Journal of Aerospace Technology and Management

Cada corpo de prova foi montado no dispositivo de ensaio e cada ensaio foi executado aplicando-se a carga P em um carregamento monotônico com uma taxa constante de 0,5 mm/min. até que o corpo de prova se rompesse. Para cada ensaio, foram coletados os dados de dois canais de extensômetros, ε1 e ε2 e um canal da carga aplicada, P. V. 1, n. 1, Jan. - Jun. 2009

Gonçalves, V. O. et al.

epóxi. O módulo em cisalhamento de compósitos com orientação ±45º é maior que os compósitos com orientação 0/90º, independentemente do tipo de reforço.

Figura 7: Corpo de prova de fibra de carbono montado no dispositivo de ensaio.

RESULTADOS E DISCUSSÕES A Tabela 1 mostra os resultados obtidos para tensão de cisalhamento no plano máxima τ12 máx. e módulo de cisalhamento no plano G12, obtidos para cada tipo de material estudado neste trabalho.

Figura 8: Tensão de cisalhamento em função da deformação para compósitos de fibra de carbono/resina epóxi ± 45º.

As Fig. 8, 9 e 10 mostram os valores de tensão máxima de cisalhamento obtidos para cada tipo de material. Para efeito de comparação, a resistência ao cisalhamento de compósitos de fibra de carbono/epóxi com orientação 0/90º mostra valores de 69 MPa e módulo de 4,2 GPa (Bezerra, 2007). Para compósitos de fibra de vidro/epóxi obtidos com orientação ±45º a resistência ao cisalhamento reportada em literatura é de 85 MPa, e módulo em cisalhamento de 19,7 GPa (Souza, 2006). Tabela 1: Média das tensões de cisalhamento máximas e dos módulos de cisalhamento. τ12 (MPa)

G12 (GPa)

Resina Epóxi

41,6 ± 6

1,4 ± 0,3

Fibra de vidro 0/90º

96,3 ± 26

7,7 ± 2,8

Fibra de carbono ± 45º

136,7 ± 19

35,7 ± 8

Os resultados mostram que os reforços com fibras de carbono ou fibras de vidro aumentam tanto a resistência como o módulo em cisalhamento de compósitos, em qualquer das configurações de reforço de 0/90º e ±45º. O módulo em cisalhamento de compósitos é no mínimo cinco vezes maior que o módulo em cisalhamento de uma resina Journal of Aerospace Technology and Management

Figura 9: Gráfico tensão em função da deformação para os cinco cdps de compósito de fibra de vidro/resina epóxi 0/90º.

Figura 10: Tensão de cisalhamento em função da de formação para resina epóxi. V. 1, n. 1, Jan. - Jun. 2009

Resistência ao cisalhamento Iosipescu em compósitos de fibra de carbono e de vidro com resina epóxi

CONCLUSÕES Os resultados obtidos, G12 e τ12, para os dois compósitos estudados e para a resina epóxi sem reforço, mostram a influência dos reforços de fibra de carbono e de vidro no aumento da resistência ao cisalhamento e do módulo de cisalhamento. A resistência ao cisalhamento dos compósitos reforçados com fibras de carbono é da mesma grandeza da resistência ao cisalhamento da resina epóxi. Isso denota que a resistência ao cisalhamento de compósitos é dominada pelas propriedades da matriz. Comparando com a resina epóxi sem reforço, os compósitos com fibra de carbono ± 45º e 0/90º apresentaram um aumento na resistência ao cisalhamento de aproximadamente 330% e 170% e no módulo de cisalhamento de 2550% e de 300%, respectivamente.

Materials”, J. Compos. Technol. Res., Vol. 21, No. 4, pp. 215-223. Khashaba, U.A., 2004, “In-Plane Shear Properties of Cross-Ply Composite Laminates With Different off-Axis Angles”, Compos. Struct., Vol. 65, No. 2, pp.167-177. Kinloch, A.J.; Young, R.J. 1995, “Fracture Behavior of Polymers”, Chapman & Hall, UK, pp. 315-317. Lessard, L.B., Eilers, O.P., Shokrieh, M.M., 1995, “Testing of in Plane Shear Properties Under Fatigue Loading”, J. Reinf. Plast. Compos. Vol. 14, No. 9, pp. 965-987. Odegard, G., Kumosa, M., 2000, “Determination of Shear Strength of Unidirectional Composite Materials with the Iosipescu and 101 Off-Axis Shear Tests”, Compos. Sci. Technol. Vol. 60, pp. 2917-2943.

Ainda, comparando com a resina epóxi sem reforço, os compósitos com fibra de vidro ± 45º e 0/90º apresentaram um aumento na resistência ao cisalhamento de aproximadamente 200 e 230% e no módulo de cisalhamento de 1400 e de 550% respectivamente.

Pindera, M. J., Ifju, P., Post, D., 1989, “Iosipescu Shear Characterization of Polymeric and Metal Matrix Composites”, Experimental Mechanics, vol. 30, No. 1, pp. 101-108.

REFERÊNCIAS

Souza, E. B., 2006, “Resistência ao cisalhamento Iosipescu do compósito laminado reforçado com tecido de fibras de vidro/epóxi”, Tese de Mestrado, Universidade Federal de Itajubá, pp. 13-33.

ASTM D 5379M/05. “Standard Test Method for Shear Properties of Composite Materials by the V-Notched Beam Method”. Bezerra, E. M., Ancellotti, A. C., Pardini, L. C., Rocco, J. A. F. F., Ilha, K., Ribeiro, C. H. C., 2007, “Artificial Neural Networks Applied to Epoxy Composites Reinforced with Carbon and E-Glass Fibers: Analysis of the Shear Mechanical Properties”, Material Science and Engineering A 464, pp. 177-185.

Tew, B.W., Odom, E. M., Teel J. D., 2001, “Composite Specimen Bearing Failure Reduction in Iosipescu Shear Tests”, Experimental Mechanics, Vol. 41, No. 3, pp. 218224. Walrath, D.E., Adans, D.F., 1983, “The Iosipescu Shear Test as Applied to Composite Materials”, Experimental Mechanics, pp. 105-110.

Dias, J. C., 2004, “Resistência ao Cisalhamento de Compósito Carbono Reforçado com Fibras de Carbono/Tecido tipo Twill”, Revista Matéria, Vol. 9, No. 4, pp. 263-270. El-Assal, A.M., Khashaba, U.A., 2007, “Fatigue Analysis of Unidirectional GFRP Composites Under Combined Bending and Torsional Loads”, Compos. Struct., Vol. 79, No. 4, pp 599-605. Ferry, L., Perreux, D., Varchon, D., Sicot, N., 1999, “Fatigue Behavior of Composite Bars Subjected to Bending and Torsion”, Compos. Sci. Technol. Vol.59, No.4, pp. 575582. Hung, S. C., Liechti, K. M., 1997, “An Evaluation of the Arcan Specimen for Determining the Shear Moduli of Fiber-reinforced Composites”, Experimental Mechanics, Vol. 37, No. 4, pp. 460-468. Hussain, A.K., Adams, D.F., 1999, “The WyomingModified Tworail Shear Test Fixture for Composite Journal of Aerospace Technology and Management

V. 1, n. 1, Jan. - Jun. 2009

Darci Cortes Pires Instituto de Aeronáutica e Espaço São José dos Campos - Brasil darci@iae.cta.br

Aparecida M. Kawamoto Instituto de Aeronáutica e Espaço São José dos Campos - Brasil cidak@iae.cta.br

Jairo Sciamareli Instituto de Aeronáutica e Espaço São José dos Campos - Brasil sciamareli@iae.cta.br

Elizabeth E.Mattos Instituto de Aeronáutica e Espaço São José dos Campos - Brasil beth@iae.cta.br

Milton F. Diniz Instituto de Aeronáutica e Espaço São José dos Campos - Brasil miltond@iae.cta.br

Rita de Cássia L. Dutra* Instituto de Aeronáutica e Espaço São José dos Campos - Brasil chefia.aqi@iae.cta.br

Koshun Iha Instituto Tecnológico da Aeronáutica São José dos Campos - Brasil koshun@ita.br

*autor para correspondência

Avaliação de agente de ligação aziridínico por meio de técnicas de análise química e instrumental Resumo: Um novo método de análise por via úmida e instrumental foi desenvolvido para avaliação da abertura do anel aziridínico do óxido de tris(1(2-metil)aziridinil) fosfina (MAPO), agente de ligação usado em propelente compósito. Foi observada redução de intensidade das bandas de absorção em 1400 e 1040 cm-1, que são características do anel aziridínico. Em alguns casos, observou-se que, quando o número de anéis abertos aumenta, a banda de absorção do grupo NH, na região 3400 e 3300 cm-1, que aparece com a abertura do anel, está localizada na região de menor número de onda. O estudo de síntese do derivado do MAPO evidenciou reações secundárias com a hidroxila do ácido 12-hidroxiesteárico, homopolimerização e reação com a umidade existente na amostra. Palavras-chave: Via úmida, FT-IR, Agente de ligação, Abertura de anel aziridínico .

Evaluation of aziridine bonding agent by means of chemical and instrumental techniques of analysis Abstract: A new method using wet chemistry and instrumental analysis has been developed for evaluating the ring-opening of aziridine tris [1-(2 methyl) aziridinyl] phosphide oxide (MAPO) of the bonding agent used in composite propellant. A reduction was observed in the intensity absorption bands in 1400 and 1040 cm-1, characteristic of aziridinic ring. It was also observed, in some cases, that when the number of open aziridinyl ring increases, the NH band in the range 3400-3300 cm-1, that appears with ring-opening, is located in the region of lower wave numbers. The study of the synthesis of MAPO derivative indicated side reactions such as homopolymerization of rings and also, with secondary hydroxyl of the 12-hydroxy stearic acid and probable humidity existent in the original sample. Key words: Wet chemistry, FT-IR, Bonding agent, Opening of aziridine ring.

INTRODUÇÃO Propulsores de veículos espaciais, também conhecidos como motores-foguetes, para cumprirem missões específicas, exigem propelentes especiais, altamente energéticos, que ofereçam alto impulso específico. O propelente sólido é uma mistura complexa e estável de compostos redutores e oxidantes que, quando entram em ignição, queimam de uma maneira homogênea, contínua e controlada, formando, a altas temperaturas, moléculas gasosas de baixa massa molar. Os gases são expelidos em alta velocidade através de uma tubeira, sistema conversor de energia térmica em energia cinética, provocando a propulsão do foguete (Klager, ____________________________________ Recebido: 23/03/09 Aceito: 05/05/09 Journal of Aerospace Technology and Management

1970). Os propelentes sólidos compósitos são constituídos por três componentes principais: uma parte orgânica, rica em carbono e hidrogênio, conhecida como “binder” ou matriz polimérica, um sal inorgânico oxidante, rico em oxigênio, e um auxiliar balístico, um metal. A matriz polimérica funciona como aglutinante das partículas sólidas e também como combustível, sendo mais utilizados atualmente os polímeros à base de polibutadieno (Carvalheira, 1995). O oxidante fornece o oxigênio necessário para a reação de combustão, e é o componente com maior peso na mistura. O oxidante mais empregado é o perclorato de amônio (AP). O auxiliar balístico, também denominado de redutor metálico, serve para aumentar a temperatura dos gases da combustão, e o mais comum é o V. 1, n. 1, Jan. - Jun. 2009

Pires, D. C. et al.

alumínio em pó. Além dos componentes básicos, as formulações de propelentes compósitos contêm outros produtos, presentes em pequena quantidade, que são os plastificantes, os catalisadores de cura e de queima, os antioxidantes, e os agentes de processamento e de ligação. A adição de um agente de ligação na composição do propelente é indispensável para assegurar e promover a interação na interface entre o AP e o “binder”, melhorando as propriedades mecânicas (Hori, 1985 e 1990). Esta interação ocorre por meio de reações químicas do “binder” com o AP ou pela atração intermolecular secundária (Hori, 1990). Estes efeitos conferem ao propelente melhor resistência à umidade e ao envelhecimento e maior resistência à tração e ao alongamento, tornando-o menos quebradiço (Klager, 1967; Wallace, 1995). O agente de ligação RELOX, denominado na literatura de BA-114 (Hamwi, 1987), é formado pela reação de substituição entre o óxido de tris(1-(2-metil)aziridinil) fosfina (MAPO) e o ácido 12-hidroxiesteárico (A. 12HE) com dois grupos funcionais distintos (hidroxila e aziridina), disponíveis para promoverem interações físicas e químicas durante o processo de fabricação, dando melhores propriedades mecânicas e prolongando a vida útil de estocagem do grão de propelente. O MAPO contém 3 anéis aziridínicos e, portanto, existe a possibilidade de um, dois ou três anéis serem abertos, ou mesmo que os 3 anéis fiquem intactos. Pode ocorrer também, que uma molécula de MAPO reaja com o anel aziridínico de outra molécula, numa reação de homopolimerização. O agente de ligação RELOX, resultante da reação, contém, ou deve conter, dois anéis aziridínicos, principal função de interesse. No propelente, estes anéis aziridínicos se abrem, ocorrendo uma homopolimerização sobre o sólido oxidante, cobrindo toda a superfície das partículas e formando uma camada firme e resistente sobre as mesmas, envolvendo-as, completamente, permitindo que se liguem à matriz polimérica (Oberth, 1995). Para avaliação dos produtos formados, é importante caracterizar a atividade química dos grupos funcionais aziridínicos e o ácido livre residual. Dentre as análises por via úmida, utilizadas na caracterização dos agentes de ligação aziridínicos, destacam-se a determinação do teor de ácido livre e a determinação do teor de imina. No caso do agente de ligação RELOX, a primeira determinação indica o limite máximo de 0,2 mg de KOH por grama de amostra, como adequado para uso nas formulações de propelentes. A determinação do teor de imina indica se o produto sintetizado possui os grupos funcionais de interesse na proporção desejada, ou seja, caracteriza a atividade do produto. Como desvantagem, na metodologia por via úmida empregada para caracterização desses materiais, o tempo de análise é consideravelmente longo, comparado a outras técnicas instrumentais. Journal of Aerospace Technology and Management

A síntese e a caracterização de agentes de ligação do tipo aziridínico (Bisol, 2007) e amínicos (Stockler, 2006), como o Tepan (tetraetileno pentamina parcialmente cianoetilada, denominado comercialmente, pela 3M, de HX-879) e Tepanol (produto de reação de TEPA, acrilonitrila e glicidol, denominado comercialmente, pela 3M, de HX878), desenvolvidos na Divisão de Química (AQI) constituem um importante programa de pesquisa do Instituto de Aeronáutica e Espaço (IAE) do Comando da Aeronáutica (CTA) (Sciamareli, 2001, 2002, 2000; Kawamoto, 2002). Os métodos alternativos desenvolvidos nos laboratórios da AQI, rápidos e confiáveis para controle da qualidade dos produtos sintetizados, são necessários para adequada aplicação nos sistemas de propelentes. Entre as técnicas instrumentais mais adequadas ao estudo de abertura de anéis aziridínicos, destaca-se a espectroscopia no infravermelho (IR). Para os reagentes e produtos da reação, a análise IR é feita por meio da identificação dos grupos funcionais formados, ou que desapareceram, durante a abertura do anel. Em trabalho anterior, foi feito um estudo sobre a homopolimerização de MAPO e a reação desse composto com resina polibutadiênica hidroxilada, utilizando-se a espectroscopia IR (Dutra. 1984). Este estudo serviu de base, juntamente com outros trabalhos que utilizaram técnicas IR (Spell. 1967; Thomas, 1964; Rahmatullah, 1992), para caracterização da abertura de anéis aziridínicos por meio da avaliação de alterações espectrométricas (deslocamento, aparecimento ou desaparecimento, aumento ou diminuição de intensidade de bandas) decorrentes das reações entre MAPO e ácido 12hidroxiesteárico. Visando contribuir com pesquisas na área de caracterização de agentes de ligação usados em propelentes, esse trabalho apresenta uma nova metodologia qualitativa, por análise química e IR na região do infravermelho médio (MIR), de 4000 a 400 cm-1, para avaliação de estruturas formadas decorrentes da reação de MAPO com o ácido 12hidroxiesteárico.

EXPERIMENTAL Síntese do Relox e seus derivados e caracterização por análise química O RELOX e seus derivados foram obtidos no Laboratório de Síntese, a partir da reação de substituição nucleofílica, nas seguintes proporções em mol (1:1, 1:2 e 1:3), de MAPO (Antrix Corporation Ltd./ISRO) com o monoácido, com agitação em rotavapor, e nas temperaturas 60 e 80ºC. O controle do produto final foi feito pela determinação de ácido livre ainda presente na mistura reacional. Os grupos aziridínicos foram determinados pelo método do tiocianato (Sciamareli, 2001). A proporção 1:1 é mostrada pelo Esquema 01. V. 1, n. 1, Jan. - Jun. 2009

Avaliação de agente de ligação aziridínico por meio de técnicas de análise química e instrumental

Análise por FT-IR As análises por Infravermelho com Transformada de Fourier (FT-IR) foram realizadas utilizando-se um espectrômetro Spectrum 2000 PerkinElmer com resolução 4 cm-1; ganho 1; 4000 a 400 cm-1 e 40 varreduras. As amostras foram analisadas por meio da técnica de transmissão, utilizando pastilha de brometo de potássio (KBr 1: 400 mg). Nesta técnica, uma pequena quantidade, normalmente 1 a 3 mg de amostra sólida triturada, é misturada com, aproximadamente, 400 mg de KBr em pó, e então prensada sob vácuo. Os discos resultantes são transparentes e adequados para obtenção de bons espectros.

abertura do anel aziridínico. Outra possibilidade da reação ser lenta seria a ausência de um catalisador adequado. O impedimento estérico em moléculas complexas é sempre um parâmetro presente, que também, pode influenciar a cinética da reação química para a abertura dos anéis. Tabela 01: Resultados (valor ácido e imina) obtidos a 60 e a 80ºC

Amostra

RX 01/2006

Tempo (dias)

Tempe- Imina anel ratura fechado (ºC) %

0,19±0,05

Derivado RELOX 02/2006

0,61±0,03

Derivado RELOX 03/2006

18,40±0,08

0,11±0,01

Derivado RELOX 06/2006

0,15±0.04

Derivado RELOX 07/2006

17,60±0,20

RELOX 05/2006

Esquema 01: Reação do MAPO com o ácido 12-hidroxiesteárico na proporção 1:1 mol

Anéis Índice acidez aziridí(mg KOH/g) nicos abertos

RESULTADOS E DISCUSSÃO Resultados de análise via úmida / associação com dados IR O índice de acidez, como variável de processo, e o teor de imina, representando a atividade química da substância, foram os parâmetros de controle da reação do A. 12HE com a aziridina do MAPO. O laboratório sintetizou os produtos RELOX, e seus dois derivados, em duas temperaturas (60 e a 80ºC). Embora, a reação seja lenta, o foco foi avaliar a presença de anel aziridínico nos três níveis de concentração de ácido (1, 2 e 3 mols de ácido 12-hidroxiestearico para 1 mol de MAPO). Foi constatado que, a 80ºC houve uma redução do teor de ácido livre, quando comparado com a reação a 60ºC, nos respectivos níveis de concentração do ácido 12hidroxiesteárico (Tab. 01). Foi observada maior conversão quando a reação é processada a 80C, sem promover a degradação dos reagentes, tornando-se a temperatura mais adequada para a síntese dos derivados aziridínicos estudados, com uma redução do tempo de síntese. A cinética com o ácido mostrou-se lenta, embora a protonação ácida de aziridinas ativadas seja rápida, mas a ausência de bom agente nucleofílico pode ter sido o principal motivo da baixa velocidade de reação, para a Journal of Aerospace Technology and Management

A metodologia usada foi a protonação e a abertura do anel pelo nucleófilo SCN .Como a reação de abertura de anéis aziridínicos é lenta na ausência do nucleófilo, a adição deste reagente é imprescindível. As análises foram realizadas após oito dias, e os resultados mostrados na Tab. 01. Na determinação dos anéis aziridínicos fechados (2), verificou-se uma conversão de 81%, numa amostra com índice de acidez de aproximadamente, 0,19 mgKOH/g. Esta conversão sugere reações secundárias, como mencionadas, na literatura, pela homopolimerização, presença de umidade e o conteúdo hidroxila (Strecker, 1968). Pelos cálculos teóricos, o valor deveria estar próximo de 100% de conversão da imina, excluindo as impurezas normais de produto comercial. Foi encontrado o valor 81% (Tabela 01- valor imina RX), devido à abertura do anel aziridínico, via reações secundárias. Para o derivado do RELOX com dois anéis abertos, sintetizado a 60ºC, observou-se uma conversão de 50% de anel aziridínico. O equivalente usado foi a própria massa molar (815 g/mol). A concentração do ácido dobrou para promover a reação de abertura do segundo anel mas, ao mesmo tempo, aumentou o seu efeito catalítico de protonação sobre a homopolimerização e a esterificação da hidroxila secundária do ácido, além da reação com a umidade existente nos reagentes. A conseqüência foi o V. 1, n. 1, Jan. - Jun. 2009

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aumento da abertura do anel por um caminho não desejado, e numa intensidade muito alta. Isto pode impedir o uso deste derivado como agente de ligação em formulações de propelentes. Dados IR, que serão discutidos posteriormente, orientaram a análise do número de anéis aziridinicos abertos após as reações de obtenção do RELOX e dos seus derivados. Como será observado adiante, o espectro IR detectou uma significativa redução da banda dos anéis fechados, sugerindo que o aumento da concentração do ácido favoreceu as reações secundárias. O valor encontrado para o ácido livre, determinado no final da reação estequiométrica em mol (1:3) entre o MAPO e o ácido, foi 18,4 mg KOH/g. Não foi observada a banda de -1 absorção em 1400 cm , então não se analisou o teor do anel aziridinico por via úmida. A interpretação para as reações secundárias podem ser explicadas pelo grande acesso de ácido livre no produto final. A imina é consumida muito mais rapidamente que o ácido, conforme mencionado por Strecker (1968), confirmando a existência de reações secundárias, e o ácido agindo como catalisador de abertura de anel pela protonação. Para os resultados obtidos a 80ºC, prevalecem os mesmos argumentos, sugerindo que o Relox pode ser obtido nesta temperatura, condição esta que manteve a reação secundária no mesmo nível que a 60ºC. A explicação é um menor efeito catalítico do ácido, no tocante à abertura do anel. O teor de ácido livre a 80ºC, ficou mais baixo, como esperado, melhorando a qualidade do produto para uso em formulações de propelentes. Como os resultados a 80ºC mostraram maior conversão, estas condições foram selecionadas para estudo por IR. Análise IR das amostras RELOX

altera as considerações feitas sobre a atribuição das alterações espectrométricas, pois o formato da banda também deve ser levado em consideração. A banda de umidade (grupo OH) é larga e a de NH, apresenta-se mais fina, conforme observado nos espectros dos derivados do RELOX. Segundo a literatura, para acompanhar reações por meio de espectrometria na região do infravermelho, métodos empíricos são empregados, com a finalidade de atribuir, de um modo aproximado, números de ondas característicos (Dutra, 1984; Spell, 1967). Pode-se citar o exemplo em que o anel reage com uma molécula pequena para produzir um outro composto. Isto produz alterações no espectro de absorção IR do produto, que resulta da abertura do anel, o qual é então comparado ao espectro da aziridina original. Este procedimento permite caracterizar os modos vibracionais associados ao grupo que reagiu. A análise de uma amostra de RX sintetizada na Divisão de Química evidenciou alterações espectrométricas IR na região 3300 a 3400 cm-1, correspondendo à absorção do grupo ―NH―, indicando a abertura do anel aziridínico do MAPO (Dutra 2002). Os três derivados do MAPO apresentaram alterações espectrométricas na região entre 3300 e 3400 cm1 , com variações de número de onda, sugerindo uma dependência em função da concentração do grupo ―NH―, previamente planejada pela adição do ácido. Uma explicação para estas alterações espectrométricas pela presença variável do grupo ―NH― é a formação de ligações de hidrogênio, levando para um de onda mais baixo (Smith, 1979). Com relação às bandas do anel aziridínico, na região de 1100 - 1330 cm-1, aparecimento e deslocamentos de bandas são observados, sem uma tendência mais nítida relacionada com o número de anéis abertos, provavelmente devido à interferência de bandas de P═O, conforme já citado (Dutra, 1984). No caso da banda em torno de 1040 cm-1, com um anel aberto, RX, a posição é a mesma do seu derivado com dois anéis abertos e o MAPO indicando a presença de anel aziridínico (Dutra, 2002).

O espectro IR do MAPO, Fig. 01, é caracterizado por um grande número de bandas, mas foram selecionadas aquelas com números de onda em 1040 e 1400 cm-1, (Dutra 1984, Strecker 1968) as quais estão relacionadas às bandas de absorção características do anel aziridínico. Estas bandas têm intensidades de absorção que variam em função do consumo do grupo durante o processo de reação. A banda (Spell, 1967) em 1250 cm-1, como uma das bandas de absorção do anel aziridínico, pode estar sobreposta à absorção do grupo P═O, que permanece inalterada em qualquer destes processos. O aparecimento da banda (Sciamareli, 2001) em 1740 cm-1, característica do grupo éster formado pela reação entre o anel aziridínico e o ácido 12-hidroxiesteárico, foi considerado como critério do progresso da reação. Deve-se ressaltar que a banda em torno de 3400 cm-1 pode ser atribuída à presença de umidade. Na tentativa de avaliar o teor de umidade da amostra, foi feita uma análise, sendo encontrado um teor de 0,13%. Entretanto este fato não Journal of Aerospace Technology and Management

Figura 01: MAPO comercial Lote SSC-263 tambor 01 Absorção do anel aziridínico, cm-1, em: 1400 1250; 1040.- bandas com intensidades variáveis. V. 1, n. 1, Jan. - Jun. 2009

Avaliação de agente de ligação aziridínico por meio de técnicas de análise química e instrumental

A Tabela 02 mostra as principais bandas IR como indicativo dos reagentes e produtos, caracterizando-os por meio da espectroscopia MIR. Na temperatura de 80ºC, Fig. 02, num período de 8 dias, na proporção 1:1 em mol, foram observadas bandas de absorção em 1400 e 1040 cm-1, menos intensas, qualitativamente, em relação ao MAPO puro, indicando abertura parcial do anel e um aumento perceptível da banda de absorção em torno de 1740 cm-1 pela formação do éster (R1COOR2). As bandas em aproximadamente, 1650 e 1540 cm-1, associadas à vibração do grupo O═P―NH, confirmam a reação de abertura do anel aziridínico. Ao serem analisados os espectros IR dos derivados com dois anéis abertos (1 mol MAPO:2 mols A. 12HE), obtidos a 80ºC, Fig. 03, num mesmo período de oito dias, observouse que continuaram a mostrar a banda em 1400 cm-1, atribuída à vibração do anel aziridínico.

Na análise de via úmida foi observado que, mesmo com apenas oito dias, aproximadamente 40% dos anéis fechados, existiam. A banda IR, em torno de 1740 cm-1, do éster formado e as absorções em 1660 e 1550 cm-1, devidas ao grupo O═P―NH, são mostradas com relativa maior intensidade quando comparadas com as respectivas bandas do RELOX.

Figura 03: Espectro IR do abertos à 80 ºC.

Figura 02: Espectro IR de RELOX derivado do Mapo com um anel aberto, à temperatura 80 ºC - bandas com intensidades variáveis.

Derivado do RELOX, dois anéis

O derivado com os três anéis abertos, planejado pela estequiometria da reação de 1 mol MAPO : 3 mols A.12HE, foi confirmado por meio do total desaparecimento da banda de absorção em 1400 cm-1, característica do anel aziridínico, Fig. 04. A ausência do anel e o grande excesso de ácido livre presentes, no final de oito dias, na temperatura de 80ºC, comprovam o consumo mais rápido do MAPO que do ácido. Chega-se à conclusão que o MAPO foi consumido por

Tabela 02: Bandas IR das substâncias estudadas (Dutra, 1984; Strecker, 1968; Smith 1979) Grupos Químicos/ Números de onda (cm-¹) Reagentes e Produtos

Anel aziridinico (cm-1)

P O (cm-1)

MAPO

1400, e 1040

1130 a 1280

A. 12HE

--------

------

Ácido O C O (cm-1)

Alcool OH/C O (cm-1)

1700 a 1720

3200 a 3500 1440,

Éster O C OR (cm-1)

O P NH (cm-1)

1155 RELOX

1400 e 1040

1154

3300, 1130 e 1075

1736

3390,1659 e 1559

Derivado: 2 Aneis abertos

1400 e 1040

1130

3300, 1130 e 1075

1736

3380, 1659 e 1559

Derivado: 3 anéis abertos

Desapareceu

1130

3300, 1130 e 1075

1736

3320, 1659 e 1559

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outras reações diferentes da esterificação. As reações secundárias da hidroxila do A.12HE, a de homopolimerização e a da umidade existente nas amostras comerciais, provavelmente foram as reações que contribuíram para o consumo mais rápido do MAPO (Strecker, 1968). As absorções dos produtos formados são evidenciadas em 1740 cm-1 do éster e 1660 e 1550 cm-1, referentes ao grupo O═P―NH, com intensidades variáveis.

Figura 04: Derivado do RX com três anéis abertos, à 80ºC

A reação entre o MAPO e o ácido 12 hidroxiesteárico para síntese de RX é uma reação de esterificação calculada estequiometricamente para a abertura de apenas um dos três anéis aziridínicos da molécula de MAPO. É uma reação de adição (Esquema 01). No espectro IR do produto formado, pode ser observada a formação da banda de absorção em torno de 1740 cm-1, indicando a formação do grupo éster, como previsto pelo tipo de reação mencionada pela literatura (Strecker, 1968), e constado experimentalmente. A intensidade desta banda se mostrou variável em função das condições planejadas pelo laboratório. Por outro lado, convém observar o aparecimento de uma banda na região de 1650cm-1 a 1540 cm-1 sugerindo a abertura do anel aziridinico para formar a ligação O═P―NH.As mesmas alterações espectrométricas IR foram observadas para os derivados obtidos a 60 ºC. A possibilidade de existirem outras reações paralelas, com formação de éster, por exemplo pelo ataque do grupo hidroxi sobre o carboxilato (reação inter ou intramolecular) deve ser considerada. Entretanto, a diminuição das bandas em 1040 e 1400 cm-1 do anel aziridínico e o aparecimento de bandas em 1650cm-1 a 1540cm-1, na região do grupo O═P―NH, reforçam que houve a reação de abertura do anel aziridínico. CONCLUSÕES l

O teor baixo de imina do RELOX sugere que houve homopolimerizaçao do MAPO

A reação de homopolimerização do MAPO é confirmada, na reação estequiométrica de aziridina e

Journal of Aerospace Technology and Management

ácido, pelo grande excesso de ácido livre no final de 8h. l

A reação processada a 60ºC contém um teor de ácido livre maior que aquela realizada a 80ºC.

Foi observada maior conversão quando a reação é processada a 80ºC, sem promover a degradação dos reagentes, sendo esta a temperatura mais adequada para a síntese dos derivados aziridínicos estudados, com uma redução do tempo de síntese.

Como os resultados a 80ºC mostraram maior conversão, estas condições foram selecionadas para estudo por IR, sendo observado que há uma redução da intensidade das bandas IR em 1400 e 1040 cm-1 quando aumenta o conteúdo COOH do meio reacional. Por outro lado, há um equivalente aumento da banda de absorção na região de 1650 a 1550 cm-1 pela formação do grupo O═P―NH.

Aparentemente, há uma tendência da banda IR, mais intensa na região de NH, em 3300 3400 cm-1, se deslocar para menor número de onda, com o aumento do número de anéis aziridínicos abertos.

REFERÊNCIAS Bisol, T.B.; Sá, M.M., 2007, “Recentes Avanços na Preparação de Aziridninas. Aplicações Sintéticas e Implicações Mecanísticas”, Química Nova, Vol.30, No. 1, pp. 106-115. Carvalheira, P., Gadiot, G. .H.J.L., Klerk, W.P.C.,1995, “Thermal Decomposition of Phase-stabilised Ammonium Nitrate (PSAN), Hydroxyl-terminated Polybutadiene (HTPB) Based Propellants. The Effect of Iron (III) Oxide Burning-rate Catalyst”, Thermochimica Acta, Vol.269270, pp.269-273. Dutra, R.C.L., 1984, “Estudo de Reação de Polibutadieno Carboxilado com Aziridina através de Espectrofotometria no Infravermelho”, Tese de Mestrado, Universidade Federal do Rio de Janeiro, 139p. Hori, K., Iwama, A., and Fukuda, T., 1985, “On the Adhesion Between Hydroxyl-Terminated Polybutadiene Fuel-Binder and Ammonium Perchlorate. Performance of Bonding Agentes”, Propellants, Explosives, Pyrotechnics, Vol.10, pp. 176-180. Hori, K., Iwama, A., and Fukuda, T., 1990, “FTIR Spectroscopic Study on the Interaction between Ammonium Perchlorate and Bonding Agents”, Propellants, Explosives, Pyrotechnics, Vol. 15, pp. 99-102. Kawamoto, A. M. and Wills, M., 2002, “Enantioselective Synthesis of Aziridines using Asymetric Transfer Hydrogenation as a Precursor for Chiral Derivatives used as V. 1, n. 1, Jan. - Jun. 2009

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Bonding Agent for Rocket Solid Propellants”, Química Nova, Vol. 25, No. 6, pp. 1-13. Klager, K., and Wrightson, J. M., 1967, “Recent Advances in Solid Propellant Binder Chemistry, Proceedings of Symposium Navigation Structure”, Mechanical Pardue University, pp. 47-74. Klager, K. and Di Millo, A. J., 1970, “Rocket Propellants” in: Encyclopédia of Polymer Science and Technology; Interscience Publishers, New York, USA, Vol.12, pp.105139.

diisopropanolamina por FTIR”, Proceedings of Encontro Técnico de Química Militar, IPqM, Rio de Janeiro, Brasil, pp. 1-10. Thomas, L. C. and Chittenden, R. A., 1964, “Characteristic Infrared Absorption Frequencies of Organophophorus -The Phophoryl (P=O) Group”, Spectrochimica Acta, Vol. 20, pp. 467-487. Wallace, Ii and Ingvar, A., 1995, “Ambient Temperature Mix, Cast, and Cure Composite Propellant Formulations”, US Patent 5472532.

Oberth, A., 1995, “Bonding Agents for HTPB-Type Solid Propellants”, US Patent 5417895. Pinto, D. V. B. S. et al, 2006, “Cura de Poliuretanos à Base de PBLH em Presença de Agente de Ligação Poliamínico”, Proceedings of 17º CBECIMat, Foz de Iguaçu, Brasil. Rahmatullah, M. S. K, Jie, L. K., Marcel, S. F., 1992, “Synthesis and Spectroscopic Properties of Long-Chain Aza, Aziridine and Azetine Fatty Esters”, JAOCS, Vol. 69, No. 4, pp. 359-362. Sayles, D., C., 1987, “Method of Generating Crosslinking Sites on the Surface of Ammonium Perchlorate in Solid Interceptor Propellantes. US Patent 4708754. Sciamareli, J., et al., 2001, “Síntese e Caracterização do Agente de Ligação Aziridínico bis (2-metel-1aziridinilisoftalimida). Anais da Associação Brasileira de Química V.50, No. 1, p.14-17. Sciamareli, J., 2001, “Síntese e Caracterização de Agentes de Ligação para Propelentes Polibutadiênico Compósitos”, Tese de Mestrado, Instituto Tecnológico da Aeronáutica, São José dos Campos, S.P., Brasil. 122p. Sciamareli, J., Takahashi, M. F. K., Teixeira, J. M. and Iha, K., 2002, “Propelente Sólido Compósito Polibutadiênico: Influência do Agente de Ligação”, Química Nova, Vol. 25, No. 1, pp. 107-110. Smith, A. L, 1979, “Applied infrared Spectroscopy”, John Wiley & Sons, New York, USA, 322 p. Spell, H. L., 1967, “The Infrared Spectra of N-Substituted Aziridine Compounds”, Analytical Chemistry, Vol. 39, No. 2, pp.185-193. Strecker, R. A. and Tompa, A. S., 1968, “Investigation of Reactions in Carboxi-Terminated Polybutadiene and Tris(1-(2-methyl)aziridinyl)phosphine Oxide”, Journal of Polymer Science, Part A-1, Vol.6, pp. 1233-1241. Takahashi, M. F. K, Sciamareli, J., Teixeira J. M. and Iha, K., 2000, “Acompanhamento da Síntese de N,NJournal of Aerospace Technology and Management

V. 1, n. 1, Jan. - Jun. 2009

Maria L. Gregori* Institute of Aeronautics and Space São José dos Campos - Brazil luisa.gregori@iae.cta.br

Edson A. Barros Technological Institute of Aeronautics São José dos Campos - Brazil barros@ita.br

Gilberto P. Filho Technological Institute of Aeronautics São José dos Campos - Brazil gilberto@ita.br

Luiz Cláudio Pardini Institute of Aeronautics and Space São José dos Campos - Brazil pardini@iae.cta.br

Sonia F. Costa Institute of Aeronautics and Space São José dos Campos - Brazil sonia@iae.cta.br

*author for correspondence

Ablative and mechanical properties of quartz phenolic composites Abstract. Quartz phenolic composites have been applied to thermal protection systems (TPSs) for reentry vehicles since the late fifties due to their excellent ablative resistance and mechanical performance. TPSs must withstand the aggressive reentry environment, such as atomic oxygen, when submitted to very high temperatures (> 1000° C) and heat flux. The ablative performance of composites is influenced by both base materials and environmental parameters during the ablation process. For TPS systems phenolic resin is usually used as the base matrix due to its ability to form a stable char during decomposition. This char plays an important role in the absorption of the heat generated during the ablation process. During re-entry, parts of the charred matrix can be abrasively removed by shear force due to high pressure and velocity. In this work the ablative and mechanical properties of quartz phenolic composites were evaluated in order to identify the range of properties suitable for the use of these materials as thermal protection systems for space vehicles. Quartz fabric having an areal weight of 680 g/m2 and a resole-type phenolic resin were used to prepare the composites. The resin has a viscosity of 165 MPa at 20°C. The prepreg material was cured by heating under pressure of 100 bar in a mold. The resin content of the prepreg obtained was about 50 per cent. The mechanical properties evaluated were, tensile, shear and flexural strength. The results obtained showed that this material has average values of 38.5 MPa, 52 MPa and 85 MPa for tensile, shear and flexural strength, respectively. The ablative tests were carried out in a high-energy air plasma in ambient atmosphere and the mass losses were measured for different exposure time. Key words: Ablation, Quartz phenolic, Mechanical properties, Thermal protection systems.

INTRODUCTION Thermal protection systems (TPS) are essential for the successful launch and operation of all spacecraft, manned or unmanned. TPS must be good enough to prevent excessive heat from destroying or damaging a vehicle or its contents. Of course the selection of a TPS depends on the spacecraft's mission. Also there are different mechanisms of thermal protection. The one investigated in this work is the ablative system. Ablative materials (or ablators) are materials used in Thermal Protection Systems (TPS) that dissipate heat generated by atmospheric friction. Ablative materials are generally employed on non reusable planetary probes. Ablative materials work by insulating a great amount of heat through a phase change. When the surface of the temperature, the resin begins to decompose and absorbs a large part of the heat, preventing it from passing to the backup materials (Sykes, 1967). The porous layer that ________________________________ Received: 27/04/09 Accepted: 25/05/09 Journal of Aerospace Technology and Management

is formed after this degradation (“char”) is very important because it acts as an insulator while the material continues to decompose and outgas (Knop, 1985 and Kanno, 1993). The char depth and the surface temperature continue to rise until at a certain surface temperature the char will be removed by mechanical shearing, melting and chemical reaction. For TPS applications, one of the most important requirements is low thermal conductivity, to prevent an increase in temperature on the back face of the composite, transferring heat to the payload structure. Ablation products injected into the flow field and surface recession alter the flow environment recession. Thus, these processes must be modeled to obtain accurate aero-thermodynamic predictions. Figure 1 shows schematically the influence of atmosphere, materials properties and aero-thermodynamic loads in the process of ablation. This paper presents preliminary mechanical properties (tensile, shear and flexural strength) and the ablative properties of a quartz phenolic composite. The ablative properties were obtained in an arc jet plasma that produces V. 1, n. 1, Jan. - Jun. 2009

Gregori, M. L. et al.

jets with gas enthalpies comparable to those encountered during atmospheric reentry. In order to analyze the microscopic aspects of the samples after exposure to the plasma, the scanning electron microscope (SEM) was used.

Mechanical tests The mechanical tests performed in this work were the tensile, shear (for “as cured” and “post-cured” samples) and flexural tests. The tensile test was carried out in an Instron universal testing machine by using the specimen geometry shown in Fig. 2, with a test speed of 0.5 mm/min. The tests were carried out by following the ASTM C1275 “Monotonic Tensile Behavior of Continuous Fiber-Reinforced Advanced Ceramics with Solid Rectangular Cross-Section Test Specimens at Ambient Temperature”.

Figur 2: Geometry of test specimen for quartz phenolic composite

Figura 1: Schematic view of the influence of atmosphere, materials properties and aero-thermodynamic loads in the ablation process

EXPERIMENTAL The material analyzed is a phenolic composite containing a bi-directional quartz fabric, having an areal weight of 680 g/m2. The properties of silica fibers, reported in literature on the manufacture are: density of 2.15 g/cm3, tensile strength of 6 GPa, tensile modulus of 78 GPa and elongation to failure of 7.7 per cent. The composite was manufactured by building up the fabric layer by layer and impregnating it with a resole-type phenolic resin.

The shear strength test was carried out in an Instron mechanical testing machine using a test speed of 0.5 mm/min . The test was carried out by following the ASTM D 5379- “Standard Test Method for Shear Properties of Composite Materials by the V-Notched Beam Method”. Although the Iosipescu test in the past was used mainly for metals, since 1992 it has been defined as the standard method for composite materials. The fixture of the sample coupon is shown in Fig. 3. The square area between notches is referred to as the test region. Figure 4 shows the geometry specimen utilized. The angle of the notches is 90°. The radius of the notch tips is 1.3 mm. The thickness of specimen was 5.5 mm.

Phenolic resin has a viscosity of 165 MPa at 20°C. The impregnation process was carried out at Plastiflow Ltd, Curitiba-PR. The prepreg material was cured by heating under pressure of 100 bar in a mold. The resin content of the prepreg obtained was around 50 per cent. The cure was carried out in a multi-stage cycle in order to increase the soaking of the fibers and the jellification process, up to the final temperature of 187°C. After soaking, the composites presented a fiber volume of 55-60 per cent. Some samples were post-cured in order to assure that the phenolic resin was completely cured. The post-cure was carried out for 12h at 180 C. The influence of the post-cure was investigated by measuring the shear properties in both cases. Journal of Aerospace Technology and Management

Figura 3: Scheme of the Iosipescu test jig V. 1, n. 1, Jan. - Jun. 2009

Ablative and mechanical properties of quartz phenolic composites

Figura 4: Sample of silica fabric with strain-gages

Figura 6: Schematic illustration of the apparatus for ablative test using an arc plasma torch

The flexural test was performed according to ASTM D790 “Standard Test Method for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials”, in four-point bending mode. The specimens have a width of 10 mm and 2.5 mm thickness. The testing set-up is shown in Fig. 5. The test speed was 1 mm/min. Flexural stress was calculated according to the following equation:

The burn-through time was measured. The erosion rate was calculated by dividing the specimen thickness or the weight change before and after the test into a burn-through time for each specimen.

(1)

One representative sample was used for each test condition. The samples were manufactured by Plastiflow Ltd. The specimens were cut in samples with diameter of 1.6 cm and thickness of 1.2 cm. RESULTS AND DISCUSSION

Figura 5: Sample geometry for flexural test Ablative test

The tensile test results are shown in Fig. 7. The tensile strength of the plain weave quartz phenolic composite was 38 5 MPa. There is a lack of available data in the literature to compare the results obtained in this work, mainly because quartz phenolic composites are used in sensitive areas of aerospace technology. (Kumara, 2005) reported 100 MPa for the tensile strength of quartz phenolic composites, which is in the range of the results found in this work. Different sorts of quartz fibers give rise to different composite properties.

A plasma torch test was performed to investigate the ablative properties of quartz phenolic composites (Fig. 6). The operation was carried out in atmospheric pressure. A DC arc plasma system was designed for continuous working at power up to 50 kW. The intensity of current was adjusted to 135A with tension of 300V. So that, the maximum achievable power obtained, due to the power supply, is about 30kW, which gives a plasma enthalpy of about 5.5MJ/kg. The gas flow was maintained at 4.5×10-3 kg/s. The specimen was placed vertically to the direction of the flame in the air. The ablative test was carried out in 10 seconds and the distance between the nozzle tip of the plasma gun and the front surface of the specimen was varied from 10 to 18 cm. The surface of the samples reached temperatures in the range of 900 to 1600C and this was measured by an optical pyrometer Mod. IR-AH 3SU Chino. Journal of Aerospace Technology and Management

Figura 7: Tensile stress for as cured samples V. 1, n. 1, Jan. - Jun. 2009

Gregori, M. L. et al.

Figures 8 and 9 show the results of the Iosipescu test. The quartz phenolic composites were prepared by stacking plain weave fabric plies and the counter-reacting forces were applied perpendicular to the 0/90Â° orientation. Considering the axis system for test specimen, the shear modulus to be measured is Gyx. The average in-plane Iosipescu shear strength and the shear modulus were measured for the as cured and post-cured samples. The Iosipescu shear strength for the as cured sample has a value of 19 2 MPa, and is shown in Figure 8. For the postcured sample, shown in Figure 9, the value is 52 2 MPa. Shear moduli were in the range of 2.5 3.5 GPa for both as cured and post-cured samples. As cured quartz phenolic composite has a higher deformation up to failure (30000 Îźm/m), compared to the post-cured one (4500 Îźm/m). This means that post-cure is beneficial for composite properties providing it is not over cured, which may lead to property degradation. The in-plane shear strength and shear modulus for laminated composites is highly dependent on the matrix properties. The curve shows a typical non-linear behavior up to failure shear stress.

Figura 9: Shear stress for post cured samples

Figure 10 shows the results of the flexural strength test. The value obtained for quartz phenolic composite was 85 25 MPa. A high scatter was found for the results which may be a result of uneven defects such as fiber misalignment in the composite.

For composites with reinforcing fibers perpendicular to the shear loading direction, the failure mode occurs mainly by fiber slipping and debonding at the fiber/matrix interface. On the other hand, in composites with reinforcing fibers parallel to the shear loading direction, the failure may occur by an interlaminar crack at the sample gage length. In any case, shear properties are mainly dominated by the matrix and the fiber/matrix interface and the failure modes are associated with shear deformation mechanism.

Figura 10: Flexural stress for as cured samples

Figure 11 shows the behavior of the surface temperature with the exposure time for different distances from the plasma torch. The temperature increases during initial phase of heating with subsequent saturation at a certain temperature which depends on the value of heat flux density. Figure 12 shows a picture of the front surface of the test specimen during testing.

Figura 8: Shear stress for as cured samples Journal of Aerospace Technology and Management

Experimental data with respect to specific mass loss rate of quartz as a function of maximum surface temperature is shown in Figure 13. It was observed that the specific mass loss rate increases exponentially with the maximum surface temperature and varies within a range of around 2.0 10-2 2 -2 2 kg/m s to 8.5 10 kg/m s. V. 1, n. 1, Jan. - Jun. 2009

Ablative and mechanical properties of quartz phenolic composites

Table 1: Burn depth as a function of testing distance for the specimens submitted to the plasma torch test

Figura 11: Surface temperature versus time

Specimen

Testing distance (cm)

Burn depth (mm)

Max. surface temp. ( C)

2,5

1600

1,0

1300

0,5

1200

0,2

920

Figure 14 shows a view of a burned surface of the quartz phenolic composite showing the aspect of the surface char generated during the burning test and the underneath fiber layer. Figure 15 shows the sample before burning and Figure 16 shows pictures of the burned surfaces of the specimens. The dark areas in the picture are the burned region of the specimens. As can be seen, the burn depth is directly related to the surface temperature and also to the heat flux in the sample. The maximum surface temperatures are shown in Table 1.

Figura 12: Front surface of the test specimen

Figura 14: Surface of the quartz phenolic composite after the plasma torch burning test

Figura 13: Specific mass loss rate as a function of maximum surface temperature

Table 1 shows the values of burn depth as a function of the distance between the nozzle tip of the plasma gun and the front surface of the specimen. The thickness of the burned surface increases as the distance decreases. The thickness of the burned surface is also a function of the exposure time of the plasma torch. Although not investigated in this work, the higher the exposure time to the plasma torch the deeper will be the burned surface of the specimen. Journal of Aerospace Technology and Management

Figura 15: Side view of the specimen before exposure to the plasma torch V. 1, n. 1, Jan. - Jun. 2009

Gregori, M. L. et al.

material has average values of 38.5 MPa, 52 MPa and 85 MPa for tensile, shear and flexural strength, respectively.

As cured and post-cured samples were analyzed for the Iosipescu shear strength and it was found that the postcured samples showed a shear strength of 19 2 MPa while for the post-cured samples the value is 52 2 Mpa. The cured quartz phenolic composite has a higher deformation up to failure (30000 μm/m), in comparison with the post-cured one (4500 μm/m). This means that postcure is beneficial for composite properties providing it is not over cured, which may lead to property degradation. It was not possible to compare the data obtained with data published in the literature because, since quartz phenolic composites are used in sensitive areas of aerospace technology, the data is not easily available in literature.

The ablative tests show that the mass loss per unit area depends strongly on the temperature of the material surface and on the distance between the nozzle tip of the plasma gun and the front surface of the specimen The information obtained from the plasma test indicates that this composite has ablation resistance and is reliable for the construction of thermal protection systems.

REFERENCES ASTM C1275, “Monotonic Tensile Behavior of Continuous Fiber-Reinforced Advanced Ceramics with Solid Rectangular Cross-Section Test Specimens at Ambient Temperature”.

ASTM D 5379, “Standard Test Method for Shear Properties of Composite Materials by the V-Notched Beam Method”. ASTM D790, “Standard Test Method for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials”. Kanno Y., 1993, “Development of Ablative Material for Planetary Entry”, Proceedings of the 9th International Conference on Composite Materials, Madrid, pp.120.

D Figura 16: Side view of the specimens subjected to the plasma torch burning test.

Knop A., Pilato L.A., 1985, “Phenolic Resin: Chemistry, Application and Performance”, Berlin: Springer-Verlag, Chapter 10. Kumara, R, Vinod, G, Renjith, S., Rajeev, G., Jana, M.K. and Harikrishnan, R., 2005, “Thermo-structural Analysis of Composite Structures”, Materials Science and Engineering, A 412, pp. 6670.

CONCLUSIONS The mechanical properties evaluated were tensile, shear and flexural strength. The results obtained showed that this Journal of Aerospace Technology and Management

Sykes, George F., 1967, “Decomposition Characteristics of a Char-forming Phenolic Polymer used for Ablative Composites”, NASA TN D3810. V. 1, n. 1, Jan. - Jun. 2009

Maurício G. Silva * Institute of Aeronautics and Space São José dos Campos - Brazil maugsilva04@yahoo.com.br

Victor O.R. Gamarra Paulista State University Guaratinguetá - Brazil victor@feg.unesp.br

Vitor Koldaev Institute of Aeronautics and Space São José dos Campos - Brazil koldaev@gmail.com

*author for correspondence

Control of Reynolds number in a high speed wind tunnel Abstract: A conceptual control model for the Reynolds number test based on isentropic relations was established for the supersonic wind tunnel. Comparison of the system response of the model simulation and the actual wind tunnel test data was made to design the control system. Two controllers were defined: the first one was based on the stagnation pressure at the settling chamber; the second was based on the relation between stagnation pressure and temperature at the settling chamber which represents the Reynolds number specified for the test. A SIMULINK® block diagram code was used to solve the mathematical model consisting of mass and energy conservation equations. Performance of the supersonic wind tunnel using a PI (proportional-plus-integral) controller was found to be satisfactory, as confirmed by the results. Key Words: Blowdown wind tunnel, Pressure control, Mach number control, Reynolds number control.

LIST OF SYMBOLS A CD Cg Cp Cv D E(s) h Ki Kp M . m P r Re SWT t T U v V θ ρ γ µ τ Subscript 1 d dif exit 0

Cross section Area Discharge coefficient Gas sizing coefficient Specific heat (constant pressure) Specific heat (constant volume) Test section diameter Error Specific Enthalpy Integral controller gain Proportional controller gain Mach number Mass flow Pressure Recovery factor Reynolds number Supersonic Wind Tunnel Time Stagnation Temperature Internal energy Velocity Volume Valve opening position Density Specific heat ratio Viscosity Static Temperature In front of shock Desired condition Diffuser Exit of diffuser Settling chamber

____________________________________ Received: 23/03/09 Accepted: 20/05/09 Journal of Aerospace Technology and Management

m² s/m J/kgK

t T TS v

Throat of nozzle Storage tank Test section Valve

J/kgK INTRODUCTION m Pa J/kg kg/s Pa s K J m/s M³ deg kg/m³ kg/s K

There are many parameters that characterize a blowdown Supersonic Wind Tunnel (SWT) such as the test section dimensions, operating characteristics (Reynolds number x Mach number), general capabilities of the facility (Mach number range, maximum stagnation pressure) and so on. Many types of tests simulated in a high-speed wind tunnel are sensitive in various degrees to the errors in Mach and Reynolds number. For example, one standard task certainly is the measurement of aerodynamic forces and moments. In this kind of test, the formation of shock waves inside the test section is expected due to the presence of the model. These waves can reflect off the walls, and may cause a detrimental effect on the measurement of forces and pressures on the tested model. Since the angle of reflection is related to the Mach number (Pope and Goin, 1965), the choice of model size is a function of the Mach number in the test section. Another restriction is the duration of the tests (run time). At a given Mach number, it is sometimes required to maximize the test duration by running the tunnel at the lowest possible stagnation pressure but still maintaining supersonic flow conditions. However, it is important to consider the undesirable variation of Reynolds number in the test section during a run. Therefore, the best choice for the stagnation pressure and temperature at a given Mach number cannot be the best choice for the Reynolds number. Due to the conflicting interrelation between these parameters it is very difficult to reproduce to estimate, theoretically, the best test configuration experimentally in V. 1, n. 1, Jan. - Jun. 2009

Silva, M.G. ; Gamarra, V.O.R.; Koldaev, V.

aeronautical components. So, it is important (stagnation pressure, geometrical configuration of nozzles and diffuser) before each experimental test run. In this context, a non-linear mathematical model was developed to analyze the open-loop system characteristics as well as for the controller design. The model for SWT was based on the mathematical model proposed by Fung (1987). Each module of SWT is formulated as an isentropic subsystem. The principal difference between this work and that proposed by Fung (1987) is that, in the present work, the Reynolds number specified for the test run is controlled. A SIMULINK® block diagram code was used to solve a mathematical model consisting of a set of ordinary differential and algebraic equations derived from the mass and energy conservation. The performance of the supersonic wind tunnel using a PI (proportional-plusintegral) controller was found to be satisfactory, as confirmed by the results.

. where ρT is the storage tank air density, mv is the mass efflux through the valve VT and is the storage tank volume. The subscript “T” refers to the storage tank. By assuming the energy loss through the valve is negligibly small, the internal energy change in the storage tank is equal to the enthalpy plus the kinetic energy through the valve. Therefore: (2) where UT is the storage tank air internal energy, hv is the specific enthalpy of the air through the valve and vv is the velocity of the air through the valve. In terms of the stagnation pressure, Eq. (2) can be written (Fung, 1987):

(3) The quotient γ =cp /cv is the specific heat ratio and R is the gas constant. The valve characteristics are described in Fisher Controls Company (1984), by the manufacturer. The mass flow at different valve positions is given by:

MATHEMATICAL FORMULATION The dynamic analysis of the control system for SWT is divided into five modules: storage tank, settling chamber nozzle, test section and diffuser, Fig. 1. Control volumes mathematically represent these modules. It is important to stress here that, in the analyses to follow, isentropic relations are assumed (no shock waves, friction and heat transfer are neglected). The change of potential energy of the gas is small and can be ignored.

(4) where Cg is the “gas sizing coefficient”. Note that, Cg =Cg (θ), where θ is the valve opening position. The variables PT and PT are the thermodynamic properties (temperature and pressure) of the air into the storage tank. ΔP is the pressure difference across the valve. It is assumed that ΔP=PT -PO , where PO is the stagnation pressure at the settling chamber. Settling Chamber

Figure 1: Blowdown Wind Tunnel (Matsumoto et al., 2001)

Storage Tank During a test, it is assumed that the mass influx from the compressor is negligible. Hence, the rate of decrease of mass in the air tank is equal to the rate of mass efflux through the valve: (1)

Journal of Aerospace Technology and Management

The second control volume is the settling chamber. Air flows into the settling chamber from the control valve and goes through the convergent-divergent nozzle to the test section. The energy entering the settling . chamber volume with mass flow mv minus the energy . exiting through the nozzle with mass flow mv is equal to the internal energy rate in the settling chamber. Therefore, the relation of energy conservation for the settling chamber is: (5) Subscript “0” refers to the settling chamber and subscript “t” refers to the throat nozzle. Rewriting the Eq.(5) in terms of stagnation pressure, results in (Fung, 1987): V. 1, n. 1, Jan. - Jun. 2009

Control of Reynolds number in a high speed wind tunnel

(6) The flow is without heat transfer. In this context, it is possible to rewrite Eq.(6):

(7) since TO =TT .

tunnel test section will be compressed and slowed down in the converging section of the diffuser, will pass through the second throat at a speed considerably below that of the test section, will begin to speed back up in the diverging portion of the diffuser, and will establish a normal shock in the diverging portion of the diffuser at a Mach number considerably below the test section Mach number, and with a correspondingly smaller loss. The design of the second throat provides the required position of shock wave at the divergent portion of nozzle. In order to estimate the run time, the movement of the shock wave at the diffuser is considered. The test run simulation is analyzed while the shock wave position is greater than the second throat position.

Nozzle The nozzle of the supersonic wind tunnel is axisymmetric, variable-geometry with converging-diverging geometry. It is assumed that the flow from the settling chamber to the test section runs an isentropic process. Considering the air as a perfect gas and the stagnation state as the reference state, . mt can be written as function of stagnation pressure and the nozzle throat area At . The maximum flow through the nozzle will be:

The shock position is obtained from the pressure ratio and area relation. The Mach number at the exit diffuser is given by:

(8)

(11)

where CD is the discharge coefficient of the nozzle, given as:

(9)

Where PO is the stagnation pressure at the test section and Pexit is the static pressure at the exit of diffuser. Pexit = Patm is adopted. The next step is to use Mexit to determine Pexit /Pafter_shock (at the diffuser) from the isentropic relations. Since Mexit < 1 , it is possible to obtain the jump relation:

The critical area At is function of the Mach number (M) desired in the test section and of its transversal section A, namely (Kuethe, 1998):

(12

  1

    1  2  2 1 1   2  M  At   M    1 A       2  

(10)

From Eq. (12) the Mach number before the shock is calculated (M1 ) using the jump relations derived for normal shock waves. WithM1 , the area relation and, consequently, the shock position are calculated.

Mach number at the Test Section and Diffuser

CONTROL PROBLEM

The Mach number at the test section is obtained from Eq.(10). With the geometrical conditions at the test section a critical area is defined considering the Mach number required by the test.

The primary reason for installing a good controller for a wind tunnel is to significantly improve flow quality in the test section. The required flow steadiness may vary with the type of tunnel. For a typical airplane test, criteria such as less than 1.0 per cent of error in Cd and Cp are usually sufficient. To meet these criteria, the Mach number steadiness in the test section must stay close to ± 0.3 per cent at M = 3.0 (Marvin, 1987). This control can be obtained in different ways. The first option is to control just the stagnation pressure of the settling chamber in order to keep the nozzle throat (At ) chocked at the design conditions. Another option is to control the Reynolds number specified for the test section.

Shocks wave are the mechanism by which most supersonic flows, including those in a wind tunnel, are slowed down. When a supersonic flow passes through a shock wave, a loss in total pressure occurs. In this context, the design of most supersonic wind tunnels includes a diffuser having a converging section; a minimum cross section zone termed the “second throat” and then a diverging section. The purpose of this design is that the flow leaving the wind Journal of Aerospace Technology and Management

V. 1, n. 1, Jan. - Jun. 2009

Silva, M.G. ; Gamarra, V.O.R.; Koldaev, V.

The present pressure control problem is relatively simple where only accuracy and stability are matters of prime concern. In this case it was judged that the complexities of optimal control, neural networks and so on, are neither necessary nor desirable for the present purposes. Stagnation Pressure in Storage Tank The objective in setting up the controller parameters for the valve is to minimize the initial transient duration to obtain as long a steady run time as possible. The control process needs a model of the pressure transmitter, the digital valve controller and the automatic ball valve to perform the SWT's control. The stagnation pressure is converted to current signal by a pressure transmitter located upstream from the nozzle. Then this signal feeds the digital valve controller. The controller has two parameters that can be changed to maintain a steady settling pressure, a proportional gain (Kp ) and an integral gain (Ki ). The complete description of the methodology used to determine the controller gains and the required performance index can be found in Fung et al. (1988). The digital valve controller compares the stagnation pressure with a set pressure and derives a corrective output signal according to the setting of these two parameters. These parameters may be modified to increase the process performance. Typically, the transfer function of the PI controller is:

Reynolds number at the test section From the preceding discussion, it is possible to control the test section condition through the control of the stagnation pressure at the settling chamber. However, during the evacuation process of air from the supply tank the stagnation temperature is not constant; moreover, this variation changes the Reynolds number significantly at the test section. In this context, a PI control system was devised based on the Reynolds number defined for the experiment. By definition, in an isentropic process:

(15)

So, the density can be evaluated from the relations (15): (16) Since: (17)

(13)

where

θ(s)

E s   P0setpo int 

it is possible to write:

is the valve opening position and P0 s  is the error signal between P0Design s  (18)

the reference input ( desired stagnation pressure at the settling chamber), and the output of the system

P s  which represents the actual pressure s  P 0 Design 0

measured. Applying the inverse Laplace transform, the differential relationship between the input and output θ(t) of the PI controller is:

Using the definitions: and

(19)

The Reynolds number can be written as a function of stagnation conditions of the flow:

(14) Journal of Aerospace Technology and Management

(20) V. 1, n. 1, Jan. - Jun. 2009

Control of Reynolds number in a high speed wind tunnel

Where the constant ξ is given by:

Settling Chamber

, and: (21) Nozzle

Viscosity is defined by: (22)

Valve Angle

The set point condition was defined in function of Reynolds number designed for the experiment, which is:

Re Setpo int  1

(23)

Finally, the controller equation which must be applied to the plant is:

(24) NUMERICAL IMPLEMENTATION

d t   dt  Ret    d  Re  K Design  p   Kp  dt Ki

  1  Ret    Re  Design  

From the preceding discussion, expressions were obtained which describe the behavior of the SWT and the control systems. These are summarized here: Storage Tank

Control Valve

The above equations become a system of six first-order nonlinear differential equations, in time, derived from the mass and energy conservation (Storage Tank, Settling Chamber, Nozzle), constitutive equation (gas and control valve) and control equations (Valve angle). There are six state variables, which are: Pt , ρt , Pο , θ, mt and mv . The inputs of this system are: test section Mach number, which results in a determined nozzle geometry; the valve position θ(Cg ), which determines the control valve behavior, according to changes in Cg ; The outputs of this system are the stagnation pressure (Pο) and temperature (Tο) in the settling chamber, angle valve (θ(t)), Mach and Reynolds number at the test section. Figures 2, 3 and 4 show schematic block diagrams relating to the SWT model, making use of a graphical editor of the MATLAB-Simulink package (Mathworks, 2002).

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V. 1, n. 1, Jan. - Jun. 2009

Silva, M.G. ; Gamarra, V.O.R.; Koldaev, V.

Ref Cg

Step

PO ConteollerRey

Wind Tunnel

Figure 2: Block diagram: Stagnation Pressure Controller

Figure 5: Wind tunnel without controller Wind Tunnel with Stagnation Pressure Control In order to compare the experimental results with those from the mathematical model simulation, the same conditions adopted by Fung (1987) were established for the present case. The research of Fung (1987) deals with the solution of the stagnation pressure control problem at the settling chamber in the SWT. This reference case is a good test to evaluate the concordance among different mathematical models. By adding a controller in a feedback loop to the wind tunnel plant, the mathematical model for the closed-loop system is established. The results are shown in Tab. 2.

Figure 3: Block diagram: Reynolds Controller

Kp Kp 1 Ref

1 s

2 PO

Integrator

1 Saturation

Table 2: Comparison of results from simulation and experimental data (PT = 260 psia)

Ki Sum 2

Mach

P0 [Psia]

Run Time [s] Experimental

Run Time [s] Present Work

2.5

RESULTS

3.0

110

The results are presented following the sequence below:

3.5

160

Sum 1

Figure 4: Block diagram: Controller Detail

- Wind tunnel without controller; - Wind tunnel with stagnation pressure control;

Wind Tunnel without Controller

It can be seen that the performance of the real wind tunnel is even better than the simulation. The reason is the assumption of an adiabatic process in the simulation. In reality, heat transfer takes place particularly through the large tank surface during the test. While the tank temperature decreases during the test, a finite amount of heat is transferred from the tank walls to the inner air. This leads to a higher tank temperature as well as a higher tank pressure than predicted by the model, Fung (1987).

Figure 5 shows a comparative picture with the plant without controller. Although the Mach number at the test section does not change during the test run (70 sec), there is a big variation in terms of Reynolds number. In this context, it is possible to conclude that Fung's wind tunnel configuration needs a control system.

Figure 6 shows the behavior of the system at Mach number 3. The results are expressed in terms of stagnation pressure and stagnation temperature at the settling chamber, stagnation pressure at the tank, Mach and Reynolds number at the test section, and the angle valve (between the tank and settling chamber). The stagnation pressure control at the

- Wind tunnel with Reynolds number control; - Temperature variation; - Shock position at the diffuser.

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V. 1, n. 1, Jan. - Jun. 2009

Control of Reynolds number in a high speed wind tunnel

settling chamber was used. It can be concluded that the control system based on the stagnation pressure at the settling chamber was found to be satisfactory, although the Reynolds number was not constant at the test section. Curiously, for this particular configuration, significant variation in angle of valve was not found. Thus, this control would be run manually. Finally, it can be observed that the constant average controller parameters found above are effective at all Mach number (2.5 to 4.0) in obtaining a response with a minimum steady-state error and overshoot with a minimum settling time.

Figure 7: Wind tunnel with Reynolds number control Shock Position Figure 8 shows the results obtained using the different types of control system adopted in this report. The shock position at the diffuser is directly dependent on stagnation pressure at the settling chamber. So, a constant location is expected during the test run if a stagnation pressure controller is adopted for the plant.

Figure 6: Wind tunnel with Stagnation Pressure control

The reason for tracking the shock wave at the diffuser is to evaluate the Mach number at the test section. The test run simulation is conducted while the shock wave position is greater than the second throat position.

Wind Tunnel with Reynolds number Control Figure 7 shows the same configuration adopted in the last section but, this time, with the Reynolds number controller. The objective is to compare the results obtained for Mach and Reynolds number at the test section using both control methodologies. Although the Mach number required to run using Fung's control system is achieved, there is a considerable difference between the methods (20 per cent approximately) in terms of Reynolds number. The principal reason for this difference is related to the temperature involved in this process. The Reynolds number controller considers the temperature variation during the transient analysis, Eq. (20), adjusting the mass ratio in a different way from the stagnation pressure control. Thus, a different angle valve variation is expected, Figs. 6 and 7. According to Pope and Goin (1965), there are two ways in which blowdown WT are customarily operated: with stagnation pressure constant or with constant mass flow. For constant mass runs the stagnation temperature must be held constant and either a heater or a thermal mass external to the tank is required. For constant stagnation pressure (settling chamber), the only control necessary is a pressure regulator that maintains the stagnation pressure constant. This report considers a relationship between stagnation pressure and (Po / To) S e t t l i n g _ C h a m b e r temperature, which characterizes the Reynolds number at the test section as control parameter at the plant. Finally, it is interesting to note that this mathematical model is an attractive tool for analyzing different test configurations, which require different control methodologies.

(a) Plant without controller

1,5

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(b) Plant with stagnation pressure controller V. 1, n. 1, Jan. - Jun. 2009

Silva, M.G. ; Gamarra, V.O.R.; Koldaev, V.

Temperature Variation during the Test Achieving constant stagnation pressure is a critical concern for supersonic wind tunnel testing. The control algorithm is designed such that it is suitable for different Mach number testing and, at the same time, obtaining the maximum test time for different stagnation pressures. However, the temperature variation is another requirement for the experimental analysis. Since the Reynolds number is a function of stagnation pressure and temperature, it is necessary to consider the temperature variation in the control algorithm as well. Figure 9 shows the different profiles when the plant without controller is considered, with stagnation pressure control and with Reynolds number control.

The curve shape and the minimum value of temperature is the principal concern. From these results it is possible to conclude that the algorithm developed for the Reynolds number controller is more efficient when flow quality and test time are considered. CONCLUSIONS A conceptual control model, based on the Reynolds number at the test section, was established for the supersonic wind tunnel. Comparison of the system response of the model simulation and the actual wind tunnel test (Fung, 1987) data was made to determine the applicability of the model. Two controllers were defined: the first one was based on the stagnation pressure at the settling chamber; the second was based on the relation (Po / To) Settling_Chamber . 1,5

Performance of the supersonic wind tunnel under different Mach numbers and stagnation pressure was tested. The following conclusions were drawn from the results of simulations:

(a) Plant without Controller

(b) Plant with Stagnation Pressure Controller Journal of Aerospace Technology and Management

(i) The isentropic approach can be used for preliminary design of the control system based on stagnation pressure at the settling chamber or Reynolds number at the test section. According to the single-loop adopted in these analyses, the second option is to be preferred since it is possible to obtain Mach and Reynolds number control simultaneously. It is important to stress here that, the principal reason in adopting the control system based on the Reynolds number at the test section is not directly related to the run time. The concern is about quality of flow. (ii) The mathematical formula applied to the normal shock wave at the diffuser can be an interesting tool to be used in analysis of run time, when the Mach number is considered as a control parameter. The cases presented in this report consider the Mach number at the diffuser greater than the Mach number at the test section. It is not a common practice. Thus, it is extremely important to analyze the stability of shock wave at the divergent portion of diffuser before defining the variable PÎżsetpoint ; V. 1, n. 1, Jan. - Jun. 2009

Control of Reynolds number in a high speed wind tunnel

(iii) After investigating different control algorithms, a single-input single-output PI controller has been chosen for this task because of its simplicity and availability. The major problem in implementing this control system is the highly nonlinear relationship of both the gas dynamics and the valve-nozzle characteristics. The linearized mathematical model was used to analyze the open-loop system characteristics as well as for the controller design. However, it is interesting to improve this mathematical model implementing the gain calculator in order to provide an automated design tool for blow-down wind tunnel testing.

REFERENCES Buggele, A. E. and Decker, A. J. , 1994, “Control of Wind Tunnel Operations Using Neural Net Interpolationof Flow Visualization Records”, NASA TechnicalMemorandum 106683. Ficher Control Company, 1984, ”Rotary Shaft Control Valve Specifications.”, Marshalltown, Iowa, Ficher Control Company Report. Fung, Y. T, 1987, “Microprocessor Control of High Speed Wind Tunnel Stagnation Pressure”, The Pensylvania State University, Master of Science, 59 p. Fung, Y. T., Settles, G. S. and Ray, A., 1988, “Microprocessor Control of High-Speed Wind Tunnel Stagnation Pressure”, AIAA Journal, Vol.2, No.14 pp429. Kuethe, A. M., Chow, C. Y., 1998, “Foundations of Aerodynamics”, Fifth Edition, John Wiley & Sons, New York. Marvin, J. G., 1987, “Wind Tunnel Requirements for Computational Fluid Dynamics Code Verification”, USA, NASA Technical Memorandum 100001. Matsumoto J., Lu, F. K. and Wilson, D. R., 2001, “Pre Programmed Controller For A Supersonic Blowdown Tunnel”, 95th Meeting of the Supersonic Tunnel Association International, Hampton, VA Pope, A., and Goin, K. L., 1965, “High Speed Wind Tunnel Testing,” John Wiley & Sons, New York. Silva, M. G., Falcao, J.B.P.F and Mello, O. A. F., “Control of High Speed Wind Tunnel Stagnation Pressure”, Proceedings of the 11th Brazilian Congress of Thermal Sciences and Engineering (ENCIT), Dec 5-8, 2006, CIT060921, Curitiba, Brasil. The MathWorks, Inc., 2002, Using Simulink (Version 5).

Journal of Aerospace Technology and Management

V. 1, n. 1, Jan. - Jun. 2009

Maria Cristina Vilela Salgado* Instituto de Aeronáutica e Espaço São José dos Campos - Brasil cristina@iae.cta.br

Mischel Carmen N. Belderrain Instituto Tecnológico de Aeronáutica São José dos Campos - Brasil carmen@ita.br

Amanda Cecília S. da Silva Instituto Tecnológico de Aeronáutica São José dos Campos - Brasil amanda@ita.br

*autor para correspondência

Avaliação do vôo tecnológico XVT02 do Veículo Lançador de Satélites VLS-1 por meio de decisão em grupo Resumo: No lançamento dos primeiros protótipos do Veículo Lançador de Satélites (VLS-1), diferentes falhas impediram o cumprimento da missão. Em 2005, foi decidido realizar novos ensaios em vôo, denominados tecnológicos, com propósito de testar os sistemas do veículo. O objetivo do trabalho é avaliar a decisão sobre a necessidade de realização do segundo vôo tecnológico, XVT02, para a continuidade e sucesso do projeto VLS-1, com base na utilização de um método multicritério de apoio à decisão. Foi aplicado um processo decisório em grupo, com especialistas de diversas áreas do projeto. A agregação de julgamentos permitiu sintetizar a decisão do grupo, cujo resultado comprovou a decisão que já havia sido tomada, ou seja, realizar os ensaios em vôo tecnológicos. Palavras-chave: Modelos de decisão, VLS (Brasil), Teoria multicritério de decisão, Decisão em grupo.

Evaluation of the technological flight XVT02 of the Satellite Vehicle Launcher VLS-1 by means of group decision Abstract: With the launch of the first prototypes of the Satellite Launch Vehicle VLS-1, different failures prevented accomplishing the mission. Then, in 2005, it was decided to carry out test flights with the purpose of testing all the systems in the vehicle. The proposal of the work is to assess the decision of conducting the second test flight XVT02 for the continuity and success of project VLS-1 based on a decision support multicriteria method. A group decision process was applied, with specialists from different areas of the project. The aggregating judgments approach led to integrate the group decision and the ensuing findings confirmed the decision taken previously, of carrying out the tests flight. Key words: Decision models, VLS (Brazil), Multicriteria decision theory, Decision groups.

INTRODUÇÃO As atividades espaciais de um país organizam-se usualmente em programas, compostos de subprogramas, projetos e atividades de caráter continuado. Ao conjunto desses programas costuma-se referir como o Programa Espacial do País. De forma análoga, no Brasil, o Programa Nacional de Atividades Espaciais (PNAE) representa o conjunto das iniciativas proposto pela Agência Espacial Brasileira (AEB) e aprovado pelo Presidente da República. As atividades espaciais requerem elevados investimentos em projetos de longa duração, mas de alto retorno esperado (PNAE, 2005). O Programa de Veículos Lançadores do Brasil tem o objetivo de capacitar o país no projeto, desenvolvimento e construção de veículos lançadores de cargas úteis, utilizando-se de foguetes de sondagem e de veículos lançadores de satélite. ____________________________________ Recebido: 05/05/09 Aceito: 26/05/09 Journal of Aerospace Technology and Management

O projeto do Veículo Lançador de Satélites (VLS-1) está inserido neste Programa. Em 2005, foi decidido realizar ensaios em vôo, denominados vôos tecnológicos VLS-1 XVT01 e VLS-1 XVT02. A finalidade do XVT01 será a de testar: a ação simultânea dos quatro propulsores do primeiro estágio; a separação do primeiro estágio; a queima do segundo estágio; e, executar uma grande quantidade de medições de parâmetros do primeiro e segundo estágios principalmente. O XVT02 testará todos os sistemas do veículo até atingir a órbita desejada, incluindo medições adicionais. O objetivo do artigo é apresentar um procedimento para estruturar a decisão, que possibilite uma avaliação, sobre a necessidade de realização do segundo vôo tecnológico XVT02, baseado em um método de apoio multicritério à decisão denominado Processo de Análise Hierárquica V. 1, n. 1, Jan. - Jun. 2009

Salgado, M.C.V., Belderrain, M.C.N., Silva, A.C.S.

(Analytic Hierarchy Process - AHP) considerando a abordagem BOCR - Benefícios, Oportunidades, Custos e Riscos. Adicionalmente, foi aplicado um processo decisório em grupo, no qual os especialistas de diversas áreas do projeto utilizaram o consenso para estabelecer os critérios para a avaliação. Para a avaliação final, os decisores efetuaram o julgamento com as suas preferências. O enfoque Agregação Individual de Julgamentos (AIJ) permitiu sintetizar a decisão em grupo. Para se alcançar o objetivo, os seguintes objetivos específicos foram estabelecidos: (a) implementação de um processo de tomada de decisão em grupo com a participação de 20 especialistas e pesquisadores de áreas diversas e com grande conhecimento do projeto; b) definição dos critérios para cada mérito: Benefícios, Oportunidades, Custos e Riscos junto ao grupo de decisores; c) utilização do método AHP para avaliar as alternativas. A pesquisa possui uma abordagem quanti-qualitativa e quanto aos objetivos, segundo Gil (1991), pode ser considerada uma pesquisa exploratória cujo procedimento técnico se constitui um estudo de caso. (Silva & Menezes, 2005) Após a presente introdução é apresentado um breve histórico do setor espacial brasileiro e uma descrição do projeto do veículo lançador de satélites (VLS-1), necessários para a compreensão da sua complexidade e, conseqüentemente, das decisões no âmbito deste projeto. A seguir é apresentado o método AHP que constitue um dos métodos AMD. Segue-se a apresentação da abordagem “Benefícios, Oportunidades, Custos e Riscos” (BOCR), conceitos de Decisão em Grupo e finalmente é apresentado o estudo de caso do XVT02. Breve histórico do setor espacial brasileiro O Programa Espacial Brasileiro iniciou-se na década de 60, em São José dos Campos, junto ao atual Comando-Geral de Tecnologia de Aeroespacial (CTA), órgão vinculado ao Ministério da Defesa (MD). As primeiras iniciativas foram de desenvolvimento de pequenos foguetes de sondagens meteorológicas para a Força Aérea. Em outubro de 1965, foi criado o Centro de Lançamento da Barreira do Inferno (CLBI). Em 1967 era lançado o primeiro protótipo do foguete brasileiro Sonda I, com a finalidade de substituir os foguetes norte-americanos de sondagens meteorológicas. Em 17 de outubro de 1969, foi criado o atual Instituto de Aeronáutica e Espaço (IAE), vinculado ao CTA, responsável pela condução de projetos de pesquisa e desenvolvimento de foguetes de sondagem. Em 1989, foi criado o Centro de Lançamento de Alcântara (CLA) no Maranhão, local escolhido, entre outros fatores, devido à posição geográfica estratégica de 2º18' ao sul da linha do equador. Esta posição possibilita, nos lançamentos Journal of Aerospace Technology and Management

em órbita geoestacionária, como demanda a grande maioria dos satélites de comunicação, um ganho de massa satelizada (carga útil) devido à maior velocidade superficial da Terra no equador. (AEB, 2007) No início de 1980, a Presidência da República aprovou a realização da Missão Espacial Completa Brasileira (MECB). A proposta estabeleceu um programa nacional integrado, visando projeto, desenvolvimento, construção e operação dos três elementos da missão de inserção de satélites em órbita: - o campo de lançamento; - o lançador de satélites; e - o satélite. Dentro desse programa, as responsabilidades foram divididas por quatro instituições: (1) ao IAE coube o desenvolvimento do VLS-1, para o transporte do satélite até a órbita especificada na missão; (2) ao Instituto Nacional de Pesquisas Espaciais (INPE), o desenvolvimento dos satélites e das estações de solo correspondentes para captação e tratamento dos dados transmitidos pelos satélites em órbita, visando o monitoramento do território brasileiro sob diversos aspectos; (3) ao CLA, o encargo de realizar as atividades referentes à operação de lançamento do VLS-1; e, (4) ao CLBI, operar como estação no acompanhamento do lançamento, com seus radares e meios de telemetria (AEB, 2007). A Agência Espacial Brasileira (AEB) foi criada em 1994. Hoje, pertence ao Ministério de Ciência e Tecnologia (MCT) e tem o objetivo de promover o desenvolvimento das atividades espaciais brasileiras e prover recursos financeiros para projetos espaciais. A AEB tem a responsabilidade de formular e implementar PNAE, cujas atividades são executadas por outras instituições governamentais que compõem o sistema como órgãos de execução, como por exemplo o CTA e o INPE e como órgãos e entidades participantes, o setor industrial e universidades brasileiras que desenvolvem pesquisas e projetos na área espacial. O Programa de Veículos Lançadores, além da capacitação de recursos humanos no país, visa estimular a inserção da indústria nacional na produção de veículos lançadores e outros bens aeroespaciais, contribuindo para a maior qualificação do parque industrial brasileiro e sua participação no competitivo mercado internacional de atividades espaciais. O Programa é composto de três subprogramas: (1) Foguetes de Sondagem; (2) Lançadores para Micro e Pequenos Satélites; e, (3) Lançadores de Satélites de Médio Porte. O VLS-1 se insere no Subprograma Lançadores para Micro e Pequenos Satélites. O Projeto VLS-1 Teve início em 1984, após o primeiro lançamento do foguete de sondagem Sonda IV (SIV) quando foram consolidados, entre outros, conhecimentos na produção do propulsor a propelente sólido de 1m de diâmetro, desenvolvimento de material (aço) de alta resistência V. 1, n. 1, Jan. - Jun. 2009

Avaliação do vôo tecnológico XVT02 do Veículo Lançador de Satélites VLS-1 por meio de decisão em grupo

estrutural e lançamento vertical a partir de plataforma. O VLS-1 é um veículo descartável e com quatro estágios propulsores na decolagem. A propulsão é garantida por motores a propelente sólido com capacidade de colocar em órbita circular equatorial, satélites de 115 kg a uma altitude de 750 km. A Figura 1 mostra o primeiro protótipo, VLS-1 V01, montado sobre a mesa de lançamento do CLA em novembro de 1997. O VLS-1 é constituído de sete subsistemas principais denominados de primeiro estágio, segundo estágio, terceiro estágio, quarto estágio, coifa ejetável, redes elétricas e redes pirotécnicas.

Características do VLS-1: Comprimento total: 19m Diâmetro dos estágios: 1 m Nº de estágios: 4 Massa Total: 50 t Massa Carga Útil: 115 kg Altitude 750 km, em órbita circular equatorial.

Figura 1: VLS-1 V01 (AEB, 2007).

O primeiro estágio é formado por quatro propulsores fixados simetricamente ao propulsor central do segundo estágio, como mostra a Fig. 2. Os quatro propulsores são acionados simultaneamente para provocar a decolagem do veículo. Cerca de cinco segundos após a queima dos propulsores, cargas pirotécnicas cortam simultaneamente toda a ligação física dos quatro motores ao segundo estágio.

com tubeira móvel. Outros subsistemas que estão no terceiro estágio são a baia de controle de rolamento (BC) e a baia de equipamentos (BE). A BC possui micropropulsores a propelente líquido que impõem uma ação de controle no eixo do veículo durante o vôo do segundo e terceiro estágios. A BE aloja o sistema inercial, computador de bordo, equipamentos relacionados ao controle e guiagem, telemetria, seqüenciamento de eventos durante o vôo e quatro micropropulsores a propelente sólido montados do lado de fora da BE para dar uma estabilidade giroscópica ao quarto estágio antes da ignição. O quarto estágio tem seu envelope motor construído de material composto, possui tubeira fixa e um cone de acoplamento para fixação do satélite. Muitos dos equipamentos para telemetria, localização e funções de terminação de vôo estão localizados no cone de acoplamento. A coifa ejetável é a estrutura que fornece ao veículo a forma aerodinâmica adequada e protege o satélite desde a fase de preparação do lançamento até o final da travessia da atmosfera. A separação da coifa ocorre no início do vôo do terceiro estágio. As redes elétricas do veículo estão compostas de quatro subredes, que são: rede elétrica de serviço, rede elétrica de telemedidas, rede elétrica de controle e a rede elétrica de segurança. As redes pirotécnicas do veículo estão compostas de três subredes, que são: rede pirotécnica de ignição, rede pirotécnica de separação e rede pirotécnica de destruição. As atividades principais durante a fase pré-lançamento ocorridas no CLA envolvem a integração e testes do veículo na plataforma de lançamento, montagem do satélite, alinhamento do veículo, carregamento e pressurização dos tanques e garrafas de gás, testes e ativação de todos os subsistemas e armação dos componentes pirotécnicos de vôo. Nos lançamentos de qualificação, o VLS-1 foi programado para cumprir a trajetória conhecida como perfil da missão, como mostra a Fig. 3. No instante inicial do lançamento, os quatro propulsores do primeiro estágio são acionados simultaneamente. Antes do fim da queima do primeiro estágio, ocorre a ignição do segundo estágio e segundos depois, a separação do primeiro estágio. O terceiro estágio é acionado 1 segundo após o fim da queima do segundo estágio e da separação deste.

Figura 2: VLS-1 (AEB, 2007).

O segundo estágio possui o propulsor e os subsistemas idênticos ao do primeiro estágio, a menos de sua tubeira móvel, mais longa, adaptada ao vôo em altitudes mais elevadas. O terceiro estágio possui o propulsor também equipado Journal of Aerospace Technology and Management

No início da queima do terceiro estágio, ocorrem a abertura e a separação da coifa ejetável de proteção do satélite. Após o fim da queima, o motor vazio do terceiro estágio e a BC são separados do veículo. O computador de bordo começa a realizar os cálculos para determinar a orientação e o instante de ignição do quarto estágio. Segue-se uma manobra que visa posicionar o conjunto quarto estágio/satélite na atitude desejada. A esta manobra dá-se o nome de basculamento. V. 1, n. 1, Jan. - Jun. 2009

Salgado, M.C.V., Belderrain, M.C.N., Silva, A.C.S.

Após a orientação do veículo, este é colocado em rotação de 2 a 3 rps (rotações por segundo) pelo sistema impulsor de rolamento, composto de quatro micropropulsores a propelente sólido denominados Propulsor Impulsor de Rolamento (PIR). Após a estabilização é feita a separação da BE.

Figura 4: Início da decolagem do VLS-1 V02 (AEB, 2007).

Para implementar estas alterações foram tomadas muitas decisões complexas que motivaram o estudo deste artigo. Os métodos de apoio multicritério à decisão (AMD)

Figura 3: Perfil da missão do VLS-1 (AEB, 2007).

Ocorre então a ignição do quarto estágio, visando dar o incremento de velocidade necessário para o satélite alcançar a órbita desejada. Ao fim de sua queima, dá-se a separação do satélite do quarto estágio e a conseqüente injeção do satélite em órbita. O tempo de duração de todos estes eventos, desde a decolagem do veículo da plataforma de lançamento até a injeção do satélite em órbita, é estimado em função da órbita desejada. Nos lançamentos do VLS-1 V01 e V02, este tempo foi estimado em aproximadamente nove minutos. O momento da decolagem do VLS-1 V02 está ilustrado na Fig. 4. Após o lançamento, ocorrem as atividades de recebimento de dados de telemetria para avaliação do vôo e as atividades da operação de retorno de equipamentos e equipes para o IAE. As atividades de avaliação do lançamento continuam no IAE, efetuando-se o tratamento dos dados obtidos na telemetria desde a decolagem do veículo até a injeção do satélite em órbita. O VLS-1 encontra-se na fase de qualificação em vôo. No relatório de avaliação das falhas ocorridas, intitulado “Relatório da Investigação do acidente ocorrido com o VLS-1 V03, em 22 de agosto de 2003, em Alcântara, Maranhão”, foram elaboradas recomendações visando à continuidade do projeto. Estas recomendações motivaram a revisão do projeto e, conseqüentemente, alteraram os ensaios que estavam previstos. Novos rumos foram traçados para o projeto e alterações no Plano de Desenvolvimento afetaram enormemente os prazos e o custo inicialmente planejados. Journal of Aerospace Technology and Management

Consiste em um conjunto de métodos e técnicas para auxiliar ou apoiar pessoas e organizações a tomar decisões, dada a multiplicidade de critérios. A distinção entre o AMD e as metodologias tradicionais de decisão é o grau de incorporação dos valores do decisor nos modelos de avaliação. (Gomes et al., 2004) O AMD aceita que a subjetividade esteja sempre presente nos processos de decisão. Uma estrutura de valores dos decisores associada aos critérios existentes permite que as alternativas sejam examinadas, avaliadas e priorizadas (Gomes et al., 2002, 2004). O uso de métodos AMD é eficaz para se chegar à melhor decisão nos vários campos da experiência humana, ciências sociais, ciências da saúde, tecnologia e outras, bem como em nossa vida pessoal. Tais métodos possuem o papel de apoio à decisão e permitem subsidiar a atividade decisória tanto por parte do decisor principal quanto dos demais stakeholders envolvidos. Segundo Clemen (1996), um processo para apoiar a decisão é útil na análise de problemas os quais, para se obter uma solução, é necessário conciliar fatores conflitantes e muitas vezes não tão bem definidos, satisfazer vários stakeholders e lidar com restrições intrínsecas ao processo. Para auxiliar este processo é preciso enfrentar os problemas como oportunidades de exercer a criatividade, de adquirir amadurecimento, desenvolvimento, aprendizado e evolução, como profissionais e como pessoas. A abordagem da oportunidade de decisão não visa a apresentar uma única verdade representada pela alternativa selecionada. Com o passar do tempo e a mudança do contexto decisório, nem sempre a melhor decisão tomada no passado é aquela que trará o melhor resultado. Assim, utilizar um método de apoio ao processo decisório não assegura o sucesso do decisor, mas ajuda a avaliar os problemas de uma forma mais estruturada e sistemática, e a decidir mais racionalmente e menos intuitivamente, V. 1, n. 1, Jan. - Jun. 2009

Avaliação do vôo tecnológico XVT02 do Veículo Lançador de Satélites VLS-1 por meio de decisão em grupo

levando a melhores resultados, diminuindo surpresas por resultados imprevistos (Gomes et al., 2006). Os métodos de apoio multicritério à decisão não buscam uma solução ótima para determinado problema, mas uma solução de compromisso, em que deve prevalecer o consenso entre as partes envolvidas (Gomes et al., 2006). Dentre os vários métodos de AMD, pode-se citar o AHP que será detalhado a seguir. O Método de Análise Hierárquica (Analytic Hierarchy Process AHP) Consiste em um dos primeiros métodos desenvolvidos para o ambiente das Decisões Multicritérios Discretas (conjunto de alternativas de decisão finito). Tem sido aplicado a uma ampla escala de situações de problemas: selecionando entre alternativas competitivas em um ambiente multi-objetivo; na alocação de recursos escassos; e, em dar prognósticos (Forman & Gass, 2001).

par dos especialistas; (3) Construção das matrizes de decisão; (4) Obtenção dos autovalores e autovetores das matrizes de decisão; (5) Determinação da Razão de consistência (RC) da matriz de decisão; (6) Verificação da consistência dos julgamentos; e, (7) Sintetização dos vetores de prioridades, como mostra a Fig. 5. Etapa 1: Estruturação do problema (Entendimento e Hierarquização): o sistema é estudado em detalhes com a finalidade de identificar o objetivo do processo decisório, os critérios e subcritérios baseados nos valores, crenças e convicções do decisor, e as alternativas para a solução do problema. Em seguida é construída a estrutura hierárquica do problema.

O AHP é um processo sistemático de estruturar o problema para melhorar sua compreensão e avaliação, e é uma maneira eficaz de verificar a consistência dos julgamentos emitidos. O método, desenvolvido por Thomas Saaty na década de 1970, inicia-se com a representação do problema em uma estrutura hierárquica, identificando o objetivo principal, os critérios e as alternativas disponíveis. A função desta fase é auxiliar a compreensão e análise do problema. Com o problema estruturado, faz-se a emissão de julgamentos de valor, em que o decisor compara, par a par, os elementos dos diversos níveis hierárquicos, para que, com cálculos que sintetizam os resultados das comparações, obtenha-se uma priorização das alternativas disponíveis em relação ao foco principal (Silva, 2006). O AHP permite a adoção de uma escala pré-definida para atribuição de valores de importância aos critérios e valores de desempenho às alternativas envolvidas, o que confere maior clareza ao processo decisório e menor subjetividade ao resultado final, como esclarecido a seguir. O método converte preferências individuais em números, cujo tratamento permite a avaliação das alternativas associadas. Os pesos resultantes são usados para classificar as alternativas e auxiliar o tomador de decisões na escolha de alternativas ou em prever um resultado.

Figura 5: Etapas do Processo de Decisão pelo Método AHP (adaptado de Oliveira e Belderrain, 2008)

O número de níveis da hierarquia é tão maior quanto maior a complexidade do problema analisado. Entretanto, deve-se considerar na estruturação do problema que a hierarquia deve ser complexa e grande o suficiente para representar a situação real, mas simples e pequena o suficiente para ser prática e utilizável. A Figura 6 representa uma estrutura hierárquica dividida em quatro níveis, com a finalidade de facilitar a compreensão e avaliação do problema.

Como a maioria dos métodos de apoio à decisão, o AHP requer avaliações numéricas. Dessa forma, critérios qualitativos serão também transformados em escalas numéricas. Em síntese, uma vez identificadas alternativas e estabelecida a avaliação segundo cada critério/subcritério, o processo de síntese das informações pode ser iniciado. O processo do método AHP consiste de sete etapas: (1) Estruturação do problema; (2) Coleta dos julgamentos par a Journal of Aerospace Technology and Management

Figura 6: Estrutura Hierárquica de Problemas Complexos (Saaty e Peniwati, (2008) V. 1, n. 1, Jan. - Jun. 2009

Salgado, M.C.V., Belderrain, M.C.N., Silva, A.C.S.

O objetivo, primeiro nível da hierarquia, é o foco principal a ser considerado na tomada de decisão. A definição do objetivo deve ser clara e específica de modo a evitar o estabelecimento de critérios (decomposição desse objetivo) e alternativas que não contribuem para a solução do real problema. Não definir corretamente o objetivo pode comprometer todo o processo de tomada de decisão. Os critérios, níveis intermediários da hierarquia, representam um detalhamento ou desmembramento do objetivo principal, que serão usados para avaliar as alternativas de solução do problema. Segue-se definindo subcritérios até que se obtenha a representação mais fiel possível do problema. As alternativas constituem o último nível da hierarquia e representam as possíveis soluções para o problema. As alternativas estão ligadas a todos os elementos do último nível que as precede, sejam eles critérios ou subcritérios. Etapa 2: Coleta dos julgamentos par a par dos especialistas: Para que se obtenha a priorização final das alternativas são atribuídos valores de importância de uma escala prédefinida aos elementos da hierarquia (critérios/subcritérios e alternativas) através de comparações par a par. A comparação par a par fundamenta-se na habilidade do ser humano de perceber o relacionamento entre elementos quantitativos e qualitativos, tangíveis e intangíveis à luz de um determinado critério. Julgar a preferência, ou importância entre dois elementos de cada vez, facilita a priorização. As comparações são efetuadas entre elementos do mesmo nível hierárquico. A cada elemento associa-se um valor de preferência sobre os outros elementos. Estes pesos são determinados por uma escala de julgamentos sugerida por Saaty variando de 1, quando os critérios são de mesma importância (igual), a 9, para importância absoluta de um critério sobre outro (extremo), conforme ilustrado na Tab. 1. Esta escala tem sido validada em muitas aplicações, apesar de sofrer também críticas sobre os valores que a compõem. Tabela 1: Questionário para comparar elementos par a par.

analisado, conectado a um único elemento de nível superior, criando uma matriz de julgamento para cada nível e cada ramo da hierarquia.

Figura 7: Matriz de decisão

Os elementos aij da matriz representam a importância relativa do elemento Ai em relação ao elemento Aj. Etapa 4: Obtenção dos autovalores e autovetores das matrizes de decisão: No método AHP, o vetor de prioridades gerado pela comparação par a par dos elementos é obtido pelo cálculo do autovetor direito associado ao autovalor máximo da matriz de decisão. Etapa 5: Determinação da Razão de Consistência (RC) da matriz de decisão: A consistência é um indicador da coerência nos julgamentos e a sua medição na matriz de comparações é um elemento importante. Este indica o quão cuidadosamente foram dadas as respostas (julgamentos) à matriz. Se RC for menor que os valores da Tab. 2, os julgamentos da matriz de decisão são considerados consistentes. Tabela 2: Valores de RC para limite aceitável de inconsistência n

0,00

<0,05

<0,09

<0,1

Por exemplo, no caso de matrizes de ordem n superior a quatro, a razão de consistência RC deverá ser menor que (10%). Etapa 6: Verificação da consistência dos julgamentos e dos níveis: Ao construir a matriz de decisão, esta é avaliada para verificação da consistência dos julgamentos e caso uma inconsistência se apresente, o analista retorna ao decisor para que este reavalie seu julgamento. Só depois de resolvidas as inconsistências, que ainda podem permanecer caso o decisor não queira alterar seu julgamento, a próxima etapa será iniciada. Conforme Saaty (1996), alguma inconsistência pode ser tolerada, visto que os seres humanos não são totalmente consistentes em seus pontos de vista.

Etapa 3: Construção das matrizes de decisão: Cada julgamento da etapa anterior deve ser organizado em uma matriz denominada matriz de decisão, de ordem igual ao número de elementos comparados, como mostra a Fig. 7.

Etapa 7: Sintetização dos vetores de prioridade: Visa determinar os vetores de prioridade que irão definir a melhor alternativa, ou a prioridade entre elas, para a solução do problema de decisão.

Os julgamentos emitidos para os elementos de um nível hierárquico, à luz do critério imediatamente superior, são compilados na forma de matriz quadrada de dimensão n, onde n é o número de elementos do nível hierárquico

O resultado do vetor prioridade da decisão pode ser obtido pela sintetização dos julgamentos de cada matriz de decisão resultante das comparações par a par de alternativas sob o ponto de vista de critérios ou subcritérios, de subcritérios

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V. 1, n. 1, Jan. - Jun. 2009

Avaliação do vôo tecnológico XVT02 do Veículo Lançador de Satélites VLS-1 por meio de decisão em grupo

com critérios de nível imediatamente superior e entre os critérios em função do objetivo fundamental.

Outra fórmula utilizada para sintetizar os resultados em um único resultado é a fórmula do resultado total, ou subtrativa ou aditiva negativa:

Segundo Saaty (2000), uma forma de estimar o vetor prioridade é multiplicar os elementos de cada linha da matriz de julgamento e extrair a raiz n-ésima deste produto, sendo n a ordem da matriz. Assim:

(4)

(1)

Onde b, o, c, r, representam os pesos dos méritos Benefícios, Oportunidades, Custos e Riscos, respectivamente, também denominados critérios de controle.

O vetor resultante deve ser normalizado para que se obtenha o vetor prioridade. (2)

Abordagem “Benefícios, Oportunidades, Custos e Riscos” (BOCR) Uma decisão, dependendo da área de atuação e da complexidade, como no caso de um desenvolvimento tecnológico, não deve ser tomada apenas por seus benefícios e custos. As oportunidades e os riscos também devem ser considerados e, se isso ocorrer, passa-se a ter quatro hierarquias com as mesmas alternativas no seu nível mais baixo. A aplicação do BOCR, introduz o conceito de prioridade negativa associado aos riscos e custos e, também, alguns novos procedimentos devem ser adotados a fim de que os resultados referentes a cada um dos méritos possam ser combinados de forma a fornecer um único resultado final. Na abordagem BOCR é construída uma estrutura hierárquica para cada mérito, como mostra a Fig. 8, e cada uma delas contém os critérios e subcritérios associados a cada mérito e as alternativas. A fim de sintetizar os resultados, aplica-se em geral a fórmula da razão ou multiplicativa que não considera a ligação dos méritos com o objetivo fundamental, ou seja, não se insere pesos diferentes para os méritos BOCR.

Neste trabalho serão utilizadas ambas as fórmulas. Decisão em Grupo Para tomar uma decisão, um indivíduo levará em consideração apenas o seu próprio ponto de vista, valores, critérios e alternativas. A decisão em grupo vem ajudar no processo de melhoria na comunicação e colaboração. A discussão do grupo para a busca da compreensão com um objetivo em comum e pelo bem coletivo, ou da empresa, ou outra finalidade, cria uma sinergia e comprometimento entre os membros que participam da decisão. Segundo Saaty e Peniwati (2008), a qualidade das decisões do grupo depende da habilidade de seus decisores para trabalhar coletivamente, o que não significa concordar, mas sim, discutir o assunto sem restrições. Melhores decisões podem ser tomadas quando opiniões diferentes aparecem, podendo ser debatidas. Isto pode levar, inclusive, a redefinições de critérios. É importante destacar que é comum em decisões em grupo que todos os decisores tenham a mesma importância relativa (pesos iguais). Mas, em alguns casos será considerado um peso maior para o decisor de maior nível hierárquico ou ao gerente do projeto, que são os maiores responsáveis; enquanto que os demais poderão ter pesos iguais. Garante-se com isso atenção especial ao ponto de vista dos maiores interessados, que podem ser incorporados clientes e usuários quando o projeto estiver na fase de produção. A criação destas assimetrias deve ser considerada com cuidado. Se o item for, no entanto, específico, a assimetria pode ser positiva. Por exemplo, no caso de um peso maior para um critério que envolva especialidade, por exemplo propulsão, em que o especialista nesta área esteja entre os decisores. EXPERIMENTAL

Figura 8 : Estrutura hierárquica BOCR

Esta razão representa o desempenho de cada alternativa i e é dada por: (3)

Journal of Aerospace Technology and Management

Estudo de caso do XVT02 O processo de análise hierárquica (AHP) consiste de 7 etapas, que serão abordadas no estudo de caso, segundo a Fig. 5. V. 1, n. 1, Jan. - Jun. 2009

Salgado, M.C.V., Belderrain, M.C.N., Silva, A.C.S.

Etapa 1: Estruturação do Problema. O objetivo fundamental definido para o estudo de caso é: Aumentar a probabilidade de sucesso no VLS-1 V04. O sucesso da missão do lançador é atingido com a inserção do satélite na órbita especificada. Para definir as alternativas de solução do problema, estão descritos os ensaios que foram inseridos no projeto: (1) ensaio de lançamento XVT01 tem a finalidade de testar a ignição simultânea dos quatro propulsores do primeiro estágio; a separação do primeiro estágio, a queima do segundo estágio e também executar uma grande quantidade de medições de parâmetros do primeiro e segundo estágios principalmente. (2) ensaio de lançamento XVT02 terá todos os estágios ativos para testar os sistemas do veículo e os eventos de vôo, até chegar à órbita especificada. Baseando-se neste contexto, decidiu-se que as alternativas para este problema de decisão são duas:

Critério 1: Qualificação de novos sistemas em vôo: existem subsistemas que deverão ser substituídos após o vôo do XVT01. O fato de esses sistemas voarem no XVT02 trará a confirmação do funcionamento como parte integrante do sistema veículo, submetidos aos rigores do ambiente de vôo, antes de aplicá-los ao V04. Critério 2: Conhecimento Adquirido: o conhecimento adquirido com a experiência de uma campanha de lançamento e com os resultados levantados no vôo de um veículo do porte do VLS-1 é um beneficio fundamental para a continuidade do Programa Espacial Brasileiro. Critério 3: Levantamento de dados de vôo: o levantamento dos dados de vôo permitirá obter informações sobre o ambiente de vôo e validar modelos teóricos de simulações de vôo. Critério 4: Constatação do funcionamento do veículo: inúmeros ensaios são realizados em solo para simular o funcionamento dos equipamentos/sistemas do veículo isoladamente. Durante o vôo os mesmos estarão integrados no sistema e submetidos ao ambiente de vôo.

(1) Realizar o XVT02 e (2) Não realizar o XVT02. Os decisores, ao fazer a escolha entre as duas alternativas para cada critério, não devem perder de vista que a alternativa escolhida visa atingir o objetivo fundamental de aumentar a probabilidade de sucesso no VLS-1 V04. A Figura 9, ilustra a estrutura hierárquica e, no nível imediatamente inferior, os méritos BOCR utilizados na avaliação do estudo de caso.

Critério 5: Operacionalidade das equipes: a operação do VLS-1 é a mais complexa dentre a dos veículos nacionais e promove a utilização de todos os recursos disponíveis. As fases preparatórias de lançamento e pós lançamento contribuem para a manutenção da aptidão dos meios e dos recursos humanos envolvidos. Critério 6: Inserção do satélite na órbita prevista: os vôos tecnológicos aumentam as chances de sucesso do vôo operacional, pois neles são sanadas deficiências do veículo e de seus meios de solo. Mérito OPORTUNIDADES

Figura 9: Estrutura hierárquica do estudo de caso

Critério 1: Estabelecimento da credibilidade do programa espacial: refere-se aos efeitos do sucesso do ensaio em vôo de um VLS-1 na credibilidade do programa espacial com respeito ao veículo lançador. O aumento da credibilidade é necessário para a continuidade dos investimentos em recursos humanos e financeiros para projetos desta natureza.

Cada mérito é uma sub-rede formada com critérios escolhidos pelos decisores, mostrados nas Fig. 10 a 13. Mérito BENEFÍCIOS

Figura 10: Estrutura hierárquica do mérito BENEFÍCIOS Journal of Aerospace Technology and Management

Figura 11: Estrutura hierárquica do mérito OPORTUNIDADES V. 1, n. 1, Jan. - Jun. 2009

Avaliação do vôo tecnológico XVT02 do Veículo Lançador de Satélites VLS-1 por meio de decisão em grupo

Critério 2: Potencialização do desenvolvimento de novos projetos: refere-se a novos projetos que promoverão o desenvolvimento tecnológico do país e que possam competir no mercado internacional de veículos lançadores. Critério 3: Projeção internacional positiva: pode se revelar importantíssima devido à necessidade de troca de experiências com centros de pesquisas internacionais e aos ganhos para o país. Este critério possui como subcritérios a parceria com centros de pesquisas e negócios lucrativos.

a inserção em órbita de satélites, com proveito pela sociedade. Critério 2: Adiamento do lançamento do VLS-1 V04: como este é o veículo que portará o satélite cliente, quanto mais testes forem feitos, mais tardio será o lançamento do V04, ou outro desenvolvimento de um novo veículo, pois as equipes de projeto e de lançamento são muito reduzidas e não há condições de preparar veículos em paralelo. Mérito RISCOS

Subcritério 1: Negócios lucrativos: na missão do IAE como uma instituição de ciência e tecnologia, o ganho é relativo ao desenvolvimento do país, com desdobramentos de natureza econômica, como se tem verificado em países como os EUA e a França, fomentando a indústria aeroespacial e a capacitação de recursos humanos. Visa também disseminar o conhecimento adquirido na sociedade e no mercado nacional, os spin-offs gerados pelos projetos de alta complexidade tecnológica, e contribuir para o desenvolvimento tecnológico do país. Subcritério 2: Parceria com centros de pesquisas: esta parceria, principalmente com os centros de pesquisas de renome internacional nas atividades espaciais, é de vital importância para o programa espacial brasileiro, traduzindo-se em beneficios através da troca de conhecimento e na parceria com projetos de interesse. Como exemplo, pode-se citar a parceria com o DLR (Agência Espacial Alemã) no desenvolvimento do VSB-30, que gerou uma excelente oportunidade de aquisição de conhecimento e de treinamento de equipes. Nesta parceria, o DLR adquire anualmente, no mínimo dois foguetes de sondagem do Brasil para atender às necessidades de lançamento de cargas úteis, em que ocorre participação de técnicos e engenheiros do IAE. Os resultados do projeto permitem sua transferência para a indústria nacional, gerando riqueza e desenvolvimento de inovação tecnológica para o país. Mérito CUSTOS

Figura 13: Estrutura hierárquica do mérito RISCOS

Critério 1: Mudança de Estratégia: refere-se ao risco de que com o passar do tempo o projeto fique sujeito a mudanças estratégicas que possam comprometer sua continuidade. Este critério possui como subcritérios a Mudança de estratégia do IAE, a Mudança de estratégia externa e a Mudança de estratégia do governo. Subcritério 1: Mudança de estratégia do IAE: refere-se às mudanças de estratégia nas prioridades do IAE que podem afetar o Projeto VLS-1. Subcritério 2: Mudança de estratégia externa: neste caso refere-se ao CTA, ao Ministério da Defesa e até mesmo a outros países que fornecem sistemas complexos e restam serviços ao Projeto VLS-1. Subcritério 3: Mudança de estratégia do governo: refere-se ao órgão financiador que cada vez mais exige resultados e questiona eventuais atrasos no projeto. Critério 2: Perda de RH qualificado: Esta é uma situação que cada vez se agrava, pois os recursos humanos qualificados estão deixando a Instituição, ora por aposentadoria ou por migrar para a iniciativa privada. Critério 3: Obsolescência tecnológica: o risco da obsolescência do veículo lançador face às necessidades do mercado mundial de compra de lançadores, que cresce e evolui rapidamente.

Figura 12: Estrutura hierárquica do mérito CUSTOS.

Critério 1: Elevação do investimento financeiro: este é um preço a ser pago pelos cofres públicos, elevando-se a cada ensaio, principalmente em vôo, que vai gerar um custo sem Journal of Aerospace Technology and Management

Critério 4: Insucesso no vôo: se o XVT02 não cumprir a missão prevista, será necessário decidir entre efetuar novo vôo tecnológico, com o conseqüente atraso do V04 ou manter o vôo operacional na seqüência. O fator decisivo será o tipo de falha ocorrida. Se for considerada mitigável, o V. 1, n. 1, Jan. - Jun. 2009

Salgado, M.C.V., Belderrain, M.C.N., Silva, A.C.S.

V04 será o próximo vôo. Este critério possui como subcritérios o Adiamento do lançamento do VLS-1 V04 e a Desmotivação. Subcritério 1: Adiamento do lançamento do VLS-1 V04: no caso de um insucesso do XVT02 e de ser decidido fazer um outro vôo tecnológico, o lançamento do V04 será mais uma vez adiado, comprometendo a qualificação e a continuidade do projeto.

Estes pesos identificam a diferença de importância entre os méritos do problema, no julgamento do grupo de decisores conforme mostrado na Fig. 15. A figura mostra um exemplo de matriz de julgamentos das alternativas de “Fazer o XVT02” à esquerda e “Não fazer o XVT02” à direita da linha de pesos, sob o critério Qualificação de novos sistemas em vôo. O peso (julgamento) foi 9 à esquerda, que significa que para este decisor, “Fazer o XVT02” é extremamente mais importante do que “Não fazer o XVT02” sob o ponto de vista do critério citado acima.

Subcritério 2: Desmotivação: um possível insucesso no XVT02, a menos que seja muito bem tratado psicologicamente, pode ser um fator determinante na motivação da equipe e causar danos na credibilidade do projeto. Critério 5: Perda de Fornecedores: refere-se à perda de fornecedores de sistemas complexos adquiridos no mercado internacional e demais sistemas e serviços no mercado nacional. Dos produtos adquiridos para o VLS-1, muitos estão fora de linha de produção das empresas fornecedoras devido à evolução dos produtos, não compensando a continuidade do fornecimento, devido à pequena demanda de aquisição. Para qualificar novos fornecedores é preciso investir tempo e recursos financeiros. Este critério possui como subcritérios a Perda de fornecedores internos e a Perda de fornecedores externos. Subcritério 1: Perda de Fornecedores Internos: refere-se aos fornecedores no mercado nacional.

Figura 15: Matriz de julgamentos das alternativas sob o critério Qualificação de novos sistemas em vôo.

A Figura 16 mostra o resultado da agregação individual de julgamentos (AIJ) entre os critérios do mérito Benefícios. Ou seja, na linha destacada da Fig. 16, pensando-se nos benefícios, a pergunta é: O critério “Constatação do funcionamento de sistemas” é quanto mais importante do que o “Levantamento de Dados”?

Subcritério 2: Perda de Fornecedores Externos: refere-se aos fornecedores no mercado internacional. Etapa 2: Coleta dos julgamentos par a par dos decisores. Nesta etapa, foram realizadas as comparações par a par dos critérios de um determinado nível, com os critérios do nível imediatamente superior. Para efetuar o julgamento, os decisores receberam um questionário com as matrizes de decisão de comparação. A Escala Fundamental de Saaty foi utilizada para representar numericamente as preferências, tanto quantitativas como qualitativas, e realizar os julgamentos par a par. Etapa 3: Construção das matrizes de decisão. Nesta etapa, constroem-se as matrizes de decisão, elaboradas com os valores dos julgamentos do grupo decisor e a matriz de pesos dos méritos BOCR, denominados b,o,c,r, mostrados na Fig. 14.

Figura 16: Matriz de julgamentos pela AIJ, de critérios do mérito BENEFÍCIOS.

A escala de pesos é visualizada na tela do Software Super Decisions. Este software foi escolhido para dar o apoio de cálculo deste trabalho pela sua acessibilidade na rede, simplicidade de utilização e por ser o método mais apropriado para o estudo de caso do projeto, auxiliando os analistas e decisores na construção dos julgamentos.

Figura 14: Matriz de decisão Journal of Aerospace Technology and Management

Etapa 4: Obtenção dos autovalores e autovetores das matrizes de decisão. Nesta etapa, realiza-se a agregação individual de julgamentos (AIJ) e os resultados V. 1, n. 1, Jan. - Jun. 2009

Avaliação do vôo tecnológico XVT02 do Veículo Lançador de Satélites VLS-1 por meio de decisão em grupo

sintetizados. Para os méritos do problema, a Tab. 3 mostra os vetores de prioridades de cada mérito, calculados pela agregação dos julgamentos dos decisores. Tabela 3: Vetor de Prioridade dos méritos BOCR. MÉRITOS Benefícios Oportunidades Custos Pesos

0,482850

0,225457

Riscos

0,113735 0,177958

Etapa 5: Determinação da Razão de Consistência (RC) da matriz de decisão. No software SuperDecisions, calcula-se a razão de consistência de cada julgamento, tanto das alternativas em função dos critérios quanto dos subcritérios em função dos critérios e dos critérios em função dos méritos. Etapa 6: Verificação da consistência dos julgamento. Nos resultados apresentados na decisão do grupo, os julgamentos inseridos nas matrizes de decisão dos critérios em função dos méritos ficaram dentro do limite de tolerância conforme pode-se observar na Fig. 17 para o mérito “BENEFÍCIOS”, quanto à matriz de decisão da Fig. 16.

Observa-se pela Tabela 5 que a sintetização revela a mesma prioridade na alternativa global para as duas fórmulas utilizadas. Tabela 5: Resultado do processo de agregação AIJ B

0,4828 0,22546

C 0,1137

F. S.

F.M.

0,1779 b*B+o*O-c*C-r*R (B*O)/(C*R)

Realizar 0,42146 0,33723 0,31935 0,23722

0,931585

0,8621399

Não 0,07854 0,11420 0,18965 0,15320 Realizar

0,06841492

0,137860

F.S. Fórmula Subtrativa F.M. Fórmula Multiplicativa

Esse resultado reflete o pensamento do grupo de decisores em torno da realização do ensaio, pela sua importância para a continuidade do projeto, contribuindo para realmente aumentar as probabilidades de sucesso no lançamento do VLS-1 V04. Figura 17: Relatório de Análise da Consistência da matriz de decisão para o mérito BENEFÍCIOS.

Etapa 7: Sintetização dos vetores de prioridade. O vetor de prioridade, resultantes da comparação entre os méritos, são utilizados para determinação da alternativa global para o cálculo através da fórmula subtrativa (4) da abordagem BOCR. A fórmula multiplicativa (3) não considera a priorização dos méritos. No caso dos custos e riscos, quanto maior os valores, na fórmula multiplicativa, o denominador vai aumentar, reduzindo o resultado final. No caso da fórmula subtrativa, os custos e riscos são subtraídos no resultado final. RESULTADOS E DISCUSSÕES

Mesmo com os valores dos custos e riscos agindo negativamente, os valores e pesos dos benefícios e oportunidades os superaram, o que significa que deve ser realizado o ensaio do XVT02, conforme mostrado na Tab. 4 . Tabela 4: Resultados dos vetores de prioridades na comparação de alternativas sob cada mérito Journal of Aerospace Technology and Management

CONCLUSÕES

O objetivo de avaliar a decisão estabelecida em 2005 no projeto VLS-1 de realizar um ensaio em vôo denominado XVT02, visando testar os sistemas do veículo lançador até chegar à órbita prevista, porém, sem transportar o satélite cliente foi atingido. Os resultados obtidos do estudo de caso mostram que a decisão do grupo se manteve, passados aproximadamente três anos da decisão tomada, pela realização do ensaio XVT02, visando a atingir com maior segurança o sucesso no projeto VLS-1. Recomenda-se avaliar as decisões tomadas, pois com o desenvolvimento do projeto e o passar do tempo, o cenário pode se modificar e aquela decisão não ser a mais adequada. A descrição do contexto do projeto VLS-1 foi necessária para a compreensão da complexidade do mesmo e, conseqüentemente, das decisões no âmbito deste projeto. Para alcançar o objetivo foi utilizado o processo de análise de decisão multicritério, em que a etapa de estruturação do problema auxilia a analise dos critérios de avaliação para V. 1, n. 1, Jan. - Jun. 2009

Salgado, M.C.V., Belderrain, M.C.N., Silva, A.C.S.

escolha ou priorização entre as alternativas estabelecidas para solução do problema. Dentre os métodos de apoio multicritério à decisão (AMD), foi escolhido, para aplicação no estudo de caso, o método AHP (Analytic Hierarchy Process), que se mostrou adequado devido à melhor adaptação das condições: (1) flexibilidade; (2) simplicidade; (3) facilidade de acesso ao software e bibliografia; (4) adequação às decisões em grupo; e, (5) adequação da abordagem BOCR com aplicação das fórmulas multiplicativa e subtrativa para calcular a avaliação global de cada alternativa, devido à natureza do estudo de caso. Após analise dos resultados, observou-se que o pensamento do grupo foi direcionado unicamente para o sucesso do projeto, independente do custo ou tempo de desenvolvimento. A etapa de estruturação do problema pode gerar uma oportunidade de discussão entre os especialistas, sendo esta uma atitude positiva e necessária para que as metas e decisões estejam sempre alinhadas com a missão da organização. Finalmente, para melhorar a eficiência nos processos de tomada de decisão de problemas complexos, esta deve ser realizada em grupo e é recomendável que se faça uma análise estruturada do problema, definindo em grupo os critérios de avaliação, as alternativas, os julgamentos e a sintetização dos resultados. Como sugestão para trabalhos futuros, propõe-se uma análise de cenários para avaliação do programa espacial brasileiro, utilizando o processo de análise de decisão multicritério. Os cenários considerados podem ser: 1. Cenários otimistas: recursos humanos qualificados em quantidade suficiente; recursos financeiros em quantidade suficientes e apoio administrativo eficiente; e, 2. Cenários pessimistas: falta de recursos humanos qualificados (fuga de cérebros); escassez de recursos financeiros; insucesso no voo do XVT01; mudança de estratégia da AEB; e, perda de fornecedores externos. O estudo poderá apoiar as decisões institucionais e governamentais sobre os caminhos a seguir, sobre a alocação de recursos, enfim, gerando uma análise profunda sob diversos aspectos, diante dos problemas atuais da instituição e do país, levando-se também em consideração o custo e o tempo de desenvolvimento para continuidade do Programa Espacial Brasileiro. AGRADECIMENTOS

REFERÊNCIAS AEB, 2005 “Programa Nacional de Atividades Espaciais PNAE”, MCT, Brasília, 114p. BRASIL. Agencia Espacial Brasileira. AEB. Disponível em: <http://www.aeb.org.br>. Acesso em: 20 nov. 2007. Clemen, R. T., 1996, “Making Hard Decisions: An Introduction to Decision Analysis”, 2ed. International Thomson, Belmont, CA, 664p. Forman, E.; Gass, I. S. 2001, “The Analytic Hierarchy Process: An Exposition. Operations Research”, Vol.49, No. 4, pp.469-486. (Electronic version). Gil, A. C., 1991, “Como Elaborar Projetos de Pesquisa”, 4 ed. Atlas, São Paulo. Gomes, L. F. A. M.; Gomes, C. F. S.; Almeida, A., 2002, “Tomada de Decisão Gerencial: Enfoque Multicritério”, Atlas, São Paulo, 157p. Gomes, L. F. A. M.; Araya, M. C. G.; Carignano, C., 2004, “Tomada de Decisões em Cenários Complexos. Pioneira” Thompson Learning, São Paulo. Gomes, L. F. A. M; Gomes, C. F. S.; Almeida, A. T., 2006, “Tomada de Decisão Gerencial: Enfoque Multicritério”, 2ed. Atlas , São Paulo. INSTITUTO DE AERONÁUTICA E ESPAÇO. IAE. Disponível em:<http://www.iae.cta.br>. Acesso em: 10 set. 2007. Oliveira, C. A.; Belderrain, M. C. N., 2008, “Considerações Sobre a Obtenção de Vetores de Prioridade no AHP”, Encuentro Nacional de Docentes de Investigación Operativa, Posadas, Argentina. Saaty, T. L., 1996, “The Analytic Hierarchy Process: Planning, Priority Setting, Resource Allocation”, RWS Publications. Pittsburg. Saaty, T. L., 2000, “Fundamentals of the Analytic Hierarchy Process”, RWS, Pittsburg. Saaty, T. L.; Peniwati, P. 2008 “Group Decision Making: Draurng Out and Reconciling Differences”, Pittsburgh: RWS, 384p. Silva, E. L.; Menezes E. M. M., 2005, “Metodologia da Pesquisa e Elaboração de Dissertação”, 4 ed., UFSC, Florianópolis, Brazil. Silva, R. C., 2006, “Proposta de Método para Priorização de Alternativas por Múltiplos Critérios”, Dissertação de Mestrado, ITA, São José dos Campos, Brazil.

Aos professores, colegas e funcionários das instituições participantes, que colaboraram com boa vontade e competência para o desenvolvimento desse trabalho. Journal of Aerospace Technology and Management

V. 1, n. 1, Jan. - Jun. 2009

Luciana P. Bassi Marinho* Institute of Aeronautics and Space São José dos Campos - Brazil lubassimp@gmail.com

Ana Cristina Avelar Institute of Aeronautics and Space São José dos Campos - Brazil anacristina@iae.cta.br

Gilberto Fisch Institute of Aeronautics and Space São José dos Campos - Brazil gfisch@iae.cta.br

Suelen T. Roballo National Institute for Space Research São José dos Campos - Brazil suelen.roballo@cptec.inpe.br

Leandro Franco Souza University of Sao Paulo São Paulo - Brazil lefraso@icmc.usp.br

Studies using wind tunnel to simulate the Atmospheric Boundary Layer at the Alcântara Space Center Abstract: The Alcântara Space Center (ASC) region has a peculiar topography due to the existence of a coastal cliff, which modifies the atmospheric boundary layer characteristic in a way that can affect rocket launching operations. Wind tunnel measurements can be an important tool for the understanding of turbulence and wind flow pattern characteristics in the ASC neighborhood, along with computational fluid dynamics and observational data. The purpose of this paper is to describe wind tunnel experiments that have been carried out by researchers from the Brazilian Institutions IAE, ITA and INPE. The technologies of Hot-Wire Anemometer and Particle Image Velocimetry (PIV) have been used in these measurements, in order to obtain information about wind flow patterns as velocity fields and vorticity. The wind tunnel measurements are described and the results obtained are presented. Key words: Alcântara Space Center (ASC), Particle image velocimetry, Turbulence, Wind flow, Wind tunnel.

Ralf Gielow National Institute for Space Research São José dos Campos - Brazil ralf.gielow@cptec.inpe.br

Roberto da Mota Girardi Technological Institute of Aeronautics São José dos Campos - Brazil girardi@ita.br *author for correspondence

LIST OF SYMBOLS

INTRODUCTION

ALA ASC ACA AEB AT CNPq

Wind regimes and atmospheric turbulence in the boundary layer have been object of great interest in Aerospace Meteorology. Serious rocket launch failures, for example, two Titan 34Ds, an Atlas Centaur, a Delta, two Arianes and a Columbia, occurred between 1985 and 2003. Several of these losses have been weather-related. In the case of Challenger, for example, the main cause was the failure of the Solid Rocket Booster (SRB) joint, caused in part by the very low temperatures experienced.

IAE IBL INPE ITA VLS PIV MIT Reδ u∞ δ

Aerodynamics Division Alcântara Space Center Atmospheric Science Division Brazilian Space Agency Anemometer Tower National Council for Scientific and Technological Development Institute of Aeronautics and Space Internal Boundary Layer National Institute for Space Research Technological Institute of Aeronautics Satellite Launcher Vehicle Particle Image Velocimetry Mobile Integration Tower Reynolds Number based on the coastal cliff height SRB - Solid Rocket Booster Streamwise wind speed Coastal cliff height

____________________________________ Received: 13/05/09 Accepted: 12/06/09 Journal of Aerospace Technology and Management

However, it has been argued that upper-wind conditions at launch time were a significant contributing factor, since severe shear-induced turbulence may well have reopened a transient SRB metal seal (Baker, 1986). According to Kingwell et al. (1991), the main meteorological factors that affect rocket operations are lightning, since electrical surges can trigger loss of control and make rockets lose control and be destroyed; temperature and humidity fields, that affect the formation of fog and ice on the vehicle; turbulence, that can impose unacceptable stresses on key structural elements such as the attachment points of hybrid V. 1, n. 1, Jan. - Jun. 2009

Marinho, L. P. B. et al.

vehicles, and wind, that can affect the electronic guidance system. Knowledge about wind flow patterns and atmospheric turbulence are important to provide basic information for Research & Development (R&D) since the rockets are designed to withstand loads due to the wind, and also trajectory, control and guidance are determined by the profile of wind near the surface. According to Fisch (1999), up to the height of 1000 m, 88 per cent of the trajectory corrections are due to the wind, while above 5000 m, this influence is only 3 per cent. In the particular case of the Brazilian Satellite Launcher Vehicle, (VLS), which is a four-stage rocket, it suffers lateral deviation in its trajectory, later compensated by the guidance system. Sounding rockets, as they are smaller, are more affected in their trajectory by the wind flow pattern. Therefore, their take-off velocity (ballistic wind lower than 6.0 m/s) is relatively small, and produces important changes in the launch azimuth due to the lateral wind speed component (Marques and Fisch, 2005). In addition, the rockets can be also affected by turbulence when positioned at the ramp, prior to the launch. Wind data is usually obtained from meteorological stations, and vertical profile measurement devices, such as anemometric towers or masts, give details of the wind in certain places. However, valuable information can be obtained from wind tunnel experiments about the modification of the atmospheric boundary layer caused by abrupt changes in local topography.

experiments that have been carried out in cooperation among researchers from IAE, ITA and INPE. These experiments have been implemented using technologies such as Hot-Wire Anemometry and Particle Image Velocimetry (PIV) in a wind tunnel, in order to investigate the wind flow pattern and turbulence at the ASC, where abrupt changes in surface roughness exist. Computational Fluid Dynamics (CFD) was also used in these investigations.

Figure 1: General view of Alcântara Space Center

R e c e n t l y, w i n d t u n n e l s h a v e b e e n u s e d i n Micrometeorology Science due to their advantage of flow control. Recent studies can be found in the literature, for example, Novak et al. (2000) analyzed the turbulent structure of the atmosphere within and above canopy. Simulations of the atmospheric wind field at a complex topography were conducted in order to plan the Naro Space Center at South Korea (Kwon et al., 2003). Studies on pollutant dispersion immersed in obstacles were carried out by Mavroidis and Griffiths (2003), and simulations of the air flow for complex topography were carried out by Cao and Tamura (2006). The Brazilian Rockets, such as the VS-40, and VSB-30 sounding rockets, and the VLS, have been launched from the Alcântara Space Center (ASC), which is located on the coast of Maranhão State, at the latitude 2° 19' S, longitude 44° 22' W, 40m above sea-level and a distance of 30 km from São Luiz. As can be observed in Fig. 1, there is a coastal cliff along the shoreline in the ASC neighborhood. Consequently, in addition to an abrupt change in roughness from the smooth oceanic surface to a rugged continental terrain, a topographical variation of 40 m is added. The Mobile Integration Tower (MIT) is located 150 m from the edge of this coastal cliff. Figure 2 shows the area of the ASC, the anemometer tower (AT) and the MIT. This paper's objective is to describe some wind tunnel Journal of Aerospace Technology and Management

. Figure 2: Detailed view of the MIT in the ASC.

Alcântara Space Center characteristics Because of the ASC's peculiar topographical characteristics, the wind, initially in balance with the oceanic surface, interacts with the low woodland vegetation (average height of the trees is 3m), modifying itself with the formation of an Internal Boundary Layer (IBL). A schematic representation of the IBL development as it moves over a smooth surface (ocean) and then across a rough surface (continent) is shown in Fig. 3. V. 1, n. 1, Jan. - Jun. 2009

Studies using wind tunnel to simulate the Atmospheric Boundary Layer at the Alcântara Space Center

The terrain's influence on the flow downstream from the cliff surface depends not only on its characteristics, but also on the characteristics of the previous surface, upstream the cliff, over which the flow was in balance. So, a new equilibrium layer is formed, the vertical thickness of which increases with the distance from the edge. Above this new layer the wind profile remains in balance with the previous surface, while within it, the wind profile is adjusted to the new surface (Stull, 1988).

wind predominates approximately up to 5000 m, with wind speeds of 7.0 ~ 8.0 m/s at levels between 1000 and 3000 m. In the dry season, the wind is predominantly from east, and reaches up to an altitude of approximately 8000 m, with wind speeds of 7.0 ~ 9.0 m/s, being particularly strong in the layer up to 2000 m, with averages between 10.0 and 10.5 m/s, and manifesting a small south-easterly rotation. This shift occurs due to intensification of the sea breeze, which displays its maximum impact (ocean-continent thermal contrast) during this period, particularly from September to November. Air temperature and the relative humidity do not present seasonal variations and their values are typical of the tropical atmosphere due to its geographic location (Fisch, 1999). BACKGROUND

Figure 3: IBL development from a smooth surface to a rough surface (adapted from Savelyev and Taylor, 2005).

The classical work of Elliot (1958) and the following theoretical and experimental studies carried out by Pendergrass and Arya (1984), Sempreviva et al. (1990), Sugita and Brutsaert (1990), Källstrand and Smedman (1997) and Jegede and Foken (1998) focused on the neutral flow problem that occurs due to the change in roughness. In these studies, the development of the modified wind flow pattern, the IBL growth and the turbulent field implications were investigated. Slvelvev and Taylor (2005) did a very detailed review of published formulas following on from Elliot's pioneering work. According to Jegede and Foken (1998), non-neutral situations can be represented by adjusting empirical coefficients of the neutral cases. Subsequently, thermal stratification effects on wind flow pattern and IBL growth were introduced, as shown by Batchvarova and Gryning (1998), Liu et al. (2000), and Hara et al. (2009). It should be mentioned that atmospheric stability at the ASC can be considered to be neutral due to the high winds. Loredo-Souza (2004) took wind tunnel measurements showing that atmospheric stability can be considered neutral if the wind speed is around 10 m/s. This is the case of the ASC (Roballo and Fisch, 2008). The vegetation in the ASC area is characteristic of a region of “restinga”. Average height of the vegetation is around 3 m. The climate presents a precipitation regime divided into two periods: (i) a wet period, with heavy rains from January to June, with March and April receiving the peak rainfalls, with monthly totals above 300 mm; and (ii) a dry period, from July to December, with precipitation lower than 15 mm per month (Fisch, 1999). There are marked differences in the wind regime between the rainy and dry season. During the wet period, the east Journal of Aerospace Technology and Management

The Atmospheric Science Division (ACA) conducts studies concerned with the atmospheric systems that occur at the ASC. In cooperation with the Aerodynamics Division (ALA) activities have begun related to the understanding of the atmospheric turbulence at the ASC using wind tunnels in another scientific project related to the upgrading of instrumentation and modernization of the aerodynamic tunnel TA-2 in order to simulate the atmospheric boundary layer. The objectives are to use TA-2 with a modern PIV system to simulate the flow at the ASC for a Reynolds number around 106. The TA-2 wind tunnel is a facility of the ALA and is Brazil's biggest aerodynamic wind tunnel. Description of the experiments The wind tunnel experiments were carried out at the Prof. Kwein Lien Feng Laboratory at the Institute of Aeronautical Technology, (ITA), using an open circuit, closed jet subsonic wind tunnel with a square test section (465 mm x 465 mm) 1200 mm in length. The maximum wind speed through the test section is 33 m/s. The atmospheric flow field was simulated by prolonging the test section, and by installing a screen and some spires as represented in Fig. 4. These spires consist of triangular steel plates, which were positioned at the entrance of the measurement chamber and combined with the roughness (felt carpet with a thickness of 3 mm was used) to produce the boundary layer profile similar to the atmospheric wind flow (Santa Catarina, 1999). Average wind speed values and fluctuations were obtained through hot-wire anemometer measurements. A schematic design of measurements using the hot-wire anemometry technique is represented in Fig. 5. A coordinate system (x,y) was used as a reference system, where the negative x values correspond to the ocean (upwind of the cliff) and the positive x values correspond to the continent (downwind). A two-dimensional PIV system was used to obtain air flow velocity fields. PIV is a very important experimental tool for fluid mechanics and aerodynamics. This technique V. 1, n. 1, Jan. - Jun. 2009

Marinho, L. P. B. et al.

allows instantaneous and non-intrusive measurement of the flow velocity, ranging from micro PIV to large industrial wind tunnel applications. As opposed to the more commonly used single-point measurements, PIV allows the spatial structure of the velocity field to be visualized as well as quantified. A good description of this technique is given by Raffel et al. (2007). The basic principle of this technique involves photographically recording the motion of microscopic particles that follow the fluid flow.

images were processed using the adaptive-correlation option of the commercial software developed by Dante Dynamics (Flow Manager 4.50.17). A 32 pixels × 32 pixels interrogation window with 50 per cent overlap and moving average validation was used. To enable the boundary layer formation in the region of optical access, and to allow PIV measurements, in addition to devices such as the spires and carpet, a screen was also used, as represented schematically in Figure 4. The experimental results were compared with numerical results obtained from the computational code named Immersed Boundary developed by Góis (2007) and Pires (2009).

Figure 4: Apparatus used for the experiments. (a)

Figure 6: PIV system installed in the wind tunnel test section.

(b)

One of the models used to simulate the ASC and the MIT (represented by a wooden block of dimensions 10 x 10 x 50 mm) is represented in Fig. 7. In order to simulate the irregularity of the coastal cliffs, experiments were made with varying inclinations. These models were painted in flat black to avoid laser reflections.

Figure 5: Overhead view of the experimental design with the coordinates x (longitudinal) and y (lateral).

To conduct the experiments, the wind tunnel test section flow was seeded with smoke particles, approximately 5mm in diameter, using a Rosco Fog generator. A New Wave NdYAG 200 mJ dual pulsed Nd:Yag laser, with a repetition rate of 15 Hz, was employed to illuminate the flow field. A vertical laser sheet was created using an articulated arm, as shown in Fig. 6, and a set of lenses for laser thickness adjustment. A 60 mm diameter Nikon lens was fitted to a 12-bit high-resolution digital camera HiSense 4M (built by Hamamatsu Photonics, Inc.) with acquisition rate of 11 Hz, spatial resolution of 2048 × 2048 pixels and 7.4 m pixel pitch was used to capture the flow field. The instantaneous Journal of Aerospace Technology and Management

Figure 7: Wind tunnel model representation. V. 1, n. 1, Jan. - Jun. 2009

Studies using wind tunnel to simulate the Atmospheric Boundary Layer at the Alcântara Space Center

Comparison between experimental and numerical simulation results Figure 8 shows a comparison between IBL height obtained from the wind tunnel experiments, for Reynolds Number based on the coastal cliff height (δ), Reδ , equal to 7.2 x 104, and the IBL height obtained from numerical simulation. For the numerical simulation and for the wind tunnel measurements, the coastal cliff was taken to be 40m in height and perpendicular to the wind direction. In the numerical simulation, a 2D model was used, with vorticityvelocity formulation. High-order compact finite-difference schemes were adopted for the derivative approximations, and a 4th order Runge-Kutta method was used to integrate time (Góis, 2007). The coastal cliff was specified through the immersed boundary method (Pires, 2009). More details about this methodology can be obtained from Pires et al. (2009). A strong correlation between the numerical and experimental results was observed, providing a validation of the numerical method adopted.

Figure 8: The IBL results from wind tunnel measurements and numerical simulation.

The streamwise wind speed (u∞) ranged from 27 to 30m/s corresponding to a Reδ , based on the height of the coastal cliff of 40 m varying from 7.2 x104 to 8 x 104. These were the maximum Reδ , values obtained in this wind tunnel. In the atmosphere, the Reδ is basically of the order of 106 and 107. Figure 9:

Average velocity profile (a) and fluctuating velocity profiles (b) along the central lane.

RESULTS Figure 9 presents the wind speed profiles (or velocity) and the fluctuation (or deviation) of the wind along the central lane (keeping the position y = 0 in Fig. 5). It is possible to observe the modification of the profiles at the cliff (position x = 0). Also, it can be noticed that the wind speed values are lower after the cliff, associated with the higher values of the fluctuation, mainly close to the surface. This is an indication of the turbulence, due to the step, up to a distance around 300 mm from the discontinuity (cliff). The bigger fluctuation values for a non-dimensional height lower than 0.2 represents the influence of the surface, which creates strong turbulence. Journal of Aerospace Technology and Management

Figure 10 presents turbulent intensity obtained with the wind speed and deviation measured at the heights corresponding to the levels of the anemometric tower (e.g. 6, 10, 16.3, 28.5, 43 and 70 m). It is possible to observe that turbulent intensity is higher close to the ground surface, specially close to the discontinuity, reaching values of 0.7 at level 1. There is also a significant decrease in turbulent intensity with height and at level 6 (equivalent to 70 m height) the turbulent intensity is around 0.1 for all positions along the central line. The distance of 300 mm is estimated as the distance where the turbulence caused by the edge disappears (Roballo, 2007). V. 1, n. 1, Jan. - Jun. 2009

Marinho, L. P. B. et al.

Figure 11: Wind profile, stream lines (a) and the vorticity (b).

Figure 10: Turbulence Intensity distribution along the central lane (position y = 0). Figure 11 shows the wind profile, the stream lines and the wind vorticity obtained from the wind tunnel measurements. The geometric structure of the coastal cliff affects the height of the IBL reaching the MIT. It is possible to observe the formation of a strong recirculation zone downwind of the coastal cliff as described before. Theoretically, the IBL height is zero at the usual change of surface roughness. However, in this present case, the coastal cliff (40 m) causes an initial height for IBL at the discontinuity (x = 0), which is in the range of 7 to 10m.

Figure 12 shows the vorticity obtained numerically. It should be noted that this simulates the real case with ReÎ´ = 2.0 x 107. It should also be noted that the higher the Re the lower the IBL height. (Pires, 2009)

The wind vorticity (Fig. 11b) ranging from -1600 to 300 s-1 was generated for the experiments in the wind tunnel. In each case a wind vorticity equal to 300 s-1 is generated by the flow when reaching the MIT and a negative vorticity (1600 s-1) is generated above the coastal cliff and the MIT (Pires, 2009).

Figure 12: Vorticity obtained in numerical simulation to ReÎ´ = 2.0 x 107.

CONCLUDING REMARKS Important information about the flow field in the region of the ASC as well as its influence on the MIT has been obtained through wind tunnel measurements in combination with numerical simulations. However, more representative results can be achieved in a wind tunnel that attains higher speeds and consequently higher Reynolds number. This will be the next step in this research, which has already commenced thanks to a grant from AEB. This project to upgrade infra-structure represents a cooperation between ALA and ACA, using the TA-2 wind tunnel facilities. Journal of Aerospace Technology and Management

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Studies using wind tunnel to simulate the Atmospheric Boundary Layer at the Alcântara Space Center

ACKNOWLEDGMENTS

Estimates”, Boundary Layer Meteorology, Vol. 85, pp. 1-33

L.B.M. Pires is grateful for support received from CNPq and CAPES, and S.T. Roballo for her Doctoral and Master of Science fellowships at INPE. G. Fisch is thankful for the support from CNPq (throughout Research Scholarship 302117/2004-0), L.F. Souza acknowledges the support of FAPESP (process 04/16064-9). The authors would like to thank the technicians José Rogério Banhara and José Ricardo Carvalho de Oliveira, both from the Aerodynamics Division, ALA, for their valuable help in this research.

Kingwell, J., Shimizu, J., Narita, K., Kawabata, H., Shimizu, I., 1991, “Weather Factors Affecting Rocket Operations: A Review and Case History”, Bulletin American Meteorological Society, Vol. 72, No. 6, pp. 778793. Kwon, K. J., Lee J. Y., Sung, B., 2003, “PIV Measurements on the Boundary Layer Flow Around Naro Space Center”, In: 5th International Symposium on Particle Image Velocimetry, Busan, Korea. PIV'03 Paper 3121, Busan, Korea.

REFERENCES Baker, D., 1986, “Why Challenger Failed”, New Scientist, pp. 52-5, 11 sep. Batchvarova, E., Gryning, S. E., 1998, “Wind Climatology, Atmospheric Turbulence and Internal Boundary-Layer Development in Athens During the Medcaphot-Trace Experiment”, Atmospheric Environment, Vol.32, No. 12, pp. 2055-2069.

Liu, H.; Chan, J. C. L., Cheng, A. Y. S., 2000, “Internal Boundary Layer Structure Under Sea-breeze Conditions in Hong Kong”, Atmospheric Environment, Vol. 35, pp. 683692. Marques, R. F. C., Fisch, G., 2005, “As Atividades de Meteorologia Aeroespacial no Centro Técnico Aerospacial (CTA)”, Boletim da Sociedade Brasileira de Meteorologia. A Meteorologia e a Aeronáutica, Vol. 29, No. 3, pp. 21-25.

Cao, S., Tamura, T., 2006, “Experimental Study on Roughness Effects on Turbulent Boundary Layer Flow Over a Two-dimensional Steep Hill”, Journal of Wind Engineering and Industrial Aerodynamics. No. 1,Vol. 94, pp. 1-19.

Mavroidis, I., Griffiths, D. J. H., 2003, “Field and Wind Tunnel Investigations of Plume Dispersion Around Single Surface Obstacles”, Atmospheric Environment, Vol. 37, No. 21, pp. 2903-2918.

Elliott, W. P., 1958, “The Growth of the Atmospheric Internal Boundary Layer”, Transactions, American Geophysical Union, Vol.39, No. 6, pp. 1048-1054.

Novak, M. D., Warland, J. S., Orchansky, A. L., Ketler, R., Green, S., 2000, “Wind Tunnel and Field Measurements of turbulent flow in forests. Part I: Uniformly Thinned Stands”, Boundary Layer Meteorology. Vol.95, No. 3, pp. 457-495.

Fisch, G., 1999, “Características do Perfil Vertical do Vento no Centro de Lançamento de Foguetes de Alcântara (CLA)”, Revista Brasileira de Meteorologia, Vol. 14, No. 1, pp. 11-21. Góis, E. R. C., 2007, “Simulação Numérica do Escoamento em Torno de Um Cilindro Utilizando o Método das Froenteiras Imersas”, Dissertação (Mestrado em Ciência da Computação e Matemática Computacional) - Universidade de São Paulo, São Carlos. Hara, T., Ohya, Y., Uchida, T., Ohba R., 2009, “WindTunnel and Numerical Simulations of the Coastal Thermal Internal Boundary Layer”, Boundary-Layer Meteorology, Vol.130, pp. 365-381.

Pendergrass, W., Arya, S. P., 1984, “Dispersion in Neutral Boundary Layer Over a Step Change in Surface Roughness I. Mean Flow and Turbulence Structure”, Atmospheric Enviroment, Vol. 18, pp. 1267-1279. Pires, L. B. M., 2009, “Estudo da Camada Limite Interna Desenvolvida em Falésias com Aplicação para o Centro de Lançamento de Alcântara”, 150f. Tese (Doutorado em Meteorologia) National Institute for Space Research, São José dos Campos. Pires, L. B. M., Souza, L. F., Fisch, G. E., Gielow, R., 2009, “Numerical Study of the Atmospheric Flow Over a Coastal Cliff”, International Journal Numerical Methods in fluids (submitted in corrections).

Jegede, O. O., Foken, T., 1998, “ A Study of the Internal Boundary Layer Due to a Roughness Change in Neutral Conditions Observed During the LINEX Field Campaigns”, Theoretical and Applied Climatology, Vol. 62, pp. 31-41.

Raffel, M., Willert, C., Wereley, S., Kompenhans J., 2007, “Particle Imaging Velocimetry; A Practical Guide”, Springer, Berlin Heidelberg New York.

Källstrand, B., Smedman, A. S., 1997, “A Case Study of the Near-neutral Coastal Internal Boundary-layer Growth: Aircraft Measurements Compared with Different Model

Roballo, S. T., 2007, “Estudo do Escoamento Atmosférico no Centro de Lançamento de Alcântara (CLA) Através de Medidas de Torre Anemométrica e em Túnel de Vento”,

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130f. Dissertação (Mestrado em Meteorologia) National Institute for Space Research, São José dos Campos. Roballo, S. T.;, Fisch, G., 2008, “Escoamento Atmosférico no Centro de Lançamento de Alcântara (CLA): Parte I Aspectos Observacionais”, Revista Brasileira de Meteorologia, Vol. 23. Santa Catarina, M. F., 1999, “Avaliação do Escoamento no Centro de Lançamento de Foguetes de Alcântara: Estudo em Túnel de Vento”, 72f. Relatório Final de Atividades de Iniciação Cientifica, Instituto Tecnológico de Aeronáutica, São José dos Campos, Brazil. Savelyev, S. A., Taylor, P. A., 2005, “Internal Boundary Layers: I. Height Formulae for Neutral and Diabatic Flows”, Boundary Layer Meteorology, Vol. 115, pp. 1-25. Sempreviva, A. M., Larsen, S. E., Mortensen, N. G., Troen, I., 1990, “Response of Neutral Boundary Layers to Change of Roughness”, Boundary-Layer Meteorology, Vol. 50, pp. 205-225. Stull, R., 1988, “An Introduction to Boundary Layer Meteorology”, London: Kluwer. Sugita, M.; Brutsaert, W., 1990, “Wind Velocity Measurements in the Neutral Boundary Layer above Hilly Prairie”, Journal of Geophysical Research, Vol. 95, No. D6, pp. 7617-7624.

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Marco F. Carvalho Torres* Instituto de Aeronáutica e Espaço São José dos Campos - Brasil mfcarvalho@iae.cta.br

Daniel Soares de Almeida Instituto de Aeronáutica e Espaço São José dos Campos - Brasil dsalmeida@iae.cta.br

Yelisetty S. Rama Krishna Instituto de Aeronáutica e Espaço São José dos Campos - Brasil krishna@iae.cta.br

Luiz Antônio Silva Instituto de Aeronáutica e Espaço São José dos Campos - Brasil silva@iae.cta.br

Wilson Kiyoshi Shimote Instituto de Aeronáutica e Espaço São José dos Campos - Brasil wilson@iae.cta.br

* autor para correspondência

Propulsão líquida no IAE: Visão das atividades e perspectivas futuras Resumo: Este trabalho apresenta as atividades na área de propulsão líquida no IAE, que teve um impulso efetivo no final da década de 90. É consenso entre os especialistas da área espacial a utilização da tecnologia de propulsão líquida nas futuras gerações de veículos lançadores de satélites, com o objetivo de elevar significativamente o desempenho do foguete e a precisão de inserção de satélites. Diversas atividades nesta área encontram-se em desenvolvimento, entre as quais podem ser citadas: os motores L5, L15 e L75, as especificações das instalações de testes de motores, componentes e estágios de foguetes, além de um programa de capacitação de recursos humanos nas áreas de projeto, fabricação e testes de motores foguetes desta natureza. Palavras-chave: Propulsão líquida, MFP, Perspectivas Futuras.

Liquid Propulsion at IAE: Vision of the activities and future perspectives Abstract: This paper presents the activities in the area of liquid propulsion, which received an effective boost at the end of the 90s. There is a consensus among specialists on the use of liquid propulsion in the next generation of satellite launcher vehicles in order to increase significantly both the performance and the satellites insertion accuracy. Several activities in this area are in development, among which should mention, the L5, the L15 and the L75 LPRE, the specifications for engine testing facilities for components and rocket stages, and a human resources program for training in the areas of liquid rocket engine design, manufacture and testing. Key words: Liquid propulsion, LPRE, Future perspectives.

LISTA DE SÍMBOLOS

INTRODUÇÃO

AEB APE FCMF GOX IAE ITA L5 L15 L75 LOX MAI MFPL MFPS MPEA

Desde os primórdios da corrida espacial, a capacidade para projetar, construir e testar motores-foguetes é considerada uma questão estratégica pelos países que desenvolvem atividades espaciais, garantindo a eles a possibilidade de equipar seus foguetes, independentemente de influências políticas externas.

MTCR PNAE

Agência Espacial Brasileira Divisão de Propulsão Espacial Fundação Casimiro Montenegro Filho Oxigênio gasoso Instituto de Aeronáutica e Espaço Instituto Tecnológico da Aeronáutica Motor-foguete a propelente líquida de 5 kN Motor-foguete a propelente líquida de 15 kN Motor-foguete a propelente líquida de 75 kN Oxigênio líquido Moscow State Aviation Institute Motor-Foguete a Propelente Líquido Motor-Foguete a Propelente Sólido Mestrado Profissionalizante em Engenharia Aeroespacial Missile Technology Control Regime Programa Nacional de Atividades Espaciais

____________________________________ Recebido: 06/05/09 Aceito: 22/05/09

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A experiência do IAE ao longo dos anos tem mostrado que adquirir motores-foguetes e seus componentes no exterior é uma tarefa extremamente delicada, pois a tecnologia de foguetes está sujeita às restrições dos países signatários do MTCR (Missile Technology Control Regime), além de sofrer embargos de natureza política, comercial e estratégica. Para superar estes obstáculos, o IAE sempre procurou atuar de forma a desenvolver seus próprios motores e tornar-se independente de influências externas. Não fosse pela visão de alguns pioneiros, que desde muito cedo, perceberam que os sistemas propulsivos deveriam receber atenção especial no desenvolvimento de nossos foguetes, talvez o Brasil estivesse atuando, hoje, apenas no desenvolvimento de V. 1, n. 1, Jan. - Jun. 2009

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satélites, como se verifica em alguns países da América Latina. Tal como nossos predecessores perceberam há cerca de 40 anos, não há como duvidar que a tecnologia de propulsão espacial foi e sempre será um dos pilares para o domínio da tecnologia de foguetes. Garantir a manutenção do que foi aprendido e ampliar a capacidade para desenvolver novos sistemas propulsivos são metas permanentes do programa espacial brasileiro, a fim de garantir nossa soberania para a utilização do espaço com fins científicos, estratégicos, comerciais ou de defesa. Contudo, para que possamos atuar efetivamente nestas áreas, será necessário um amplo desenvolvimento de novas tecnologias para atender missões espaciais com requisitos de desempenho e precisão cada vez mais rígidos.

axialmente, dependendo da geometria, consumindo todo o propelente (Oliveira, 2008). Entre o envelope motor e o propelente, existe uma proteção térmica constituída por uma camada de borracha e um revestimento adesivo (liner), com a finalidade de não permitir que a alta temperatura dos gases da combustão do propelente danifique o envelope motor, o qual integra a estrutura do foguete. O ignitor tem a função de iniciar a combustão do propelente dentro da câmara, enquanto o propelente e o isolante interno protegem o envelope motor dos gases quentes. A tubeira converte a energia térmica dos gases da combustão em energia cinética para geração de empuxo.

Da mesma forma que a tecnologia de sistemas propulsivos a propelente sólido garantiu o início da era espacial no Brasil, a tecnologia de sistemas propulsivos a propelente líquido deverá consolidar uma nova realidade que viabilizará o desenvolvimento de uma nova geração de foguetes no país.

Já em um Motor-Foguete a Propelente Líquido (MFPL), combustível e oxidante no estado líquido são estocados em tanques distintos e, durante a operação do motor, ambos são injetados na câmara de combustão para a queima. Os gases quentes, resultantes da combustão, são acelerados até velocidades supersônicas em uma tubeira para geração de empuxo.

Diversas ações foram e continuam sendo implementadas de forma a capacitar o IAE a atuar neste novo cenário tecnológico. Basicamente, essas ações têm sido orientadas para três direções: formação de pessoal especializado, construção de instalações de testes e desenvolvimento de tecnologias de fabricação.

Os elementos básicos da câmara de empuxo são o cabeçote de injeção, a câmara de combustão, a tubeira, o sistema de ignição, os sistemas de alimentação e distribuição dos propelentes.

Como resultados dessas ações podem-se citar: formação de mestres por meio de um programa de Mestrado Profissionalizante em Engenharia Aeroespacial MPEA em parceria com o ITA, MAI (Moscow Aviation Institute) e contando com o apoio da Fundação Casimiro Montenegro Filho FCMF; projetos de motores-foguete; ampliação da capacidade de realização de ensaios; contratos internacionais para serviços de consultoria em especialidades não totalmente dominadas por pesquisadores do IAE; e parcerias com empresas nacionais para pesquisa e desenvolvimento de tecnologias de fabricação. Motores-foguetes para propulsão espacial Um motor-foguete a propelente sólido (MFPS) é uma classe de motor de aplicação espacial em que o propelente, mistura heterogênea de combustível e oxidante, preenche quase totalmente um vaso de pressão denominado envelope motor. O propelente é preparado e moldado no envelope motor com geometria interna no formato do mandril de carregamento, projetado de forma a atender as especificações da curva de empuxo necessária. Após a cura do propelente, o mandril é retirado e o bloco de propelente adquire características de um material visco elástico, podendo este bloco ter geometria interna em diversos formatos como, por exemplo, estrela, roda de vagão, cigarro, etc. Uma vez que o propelente é ignitado, a chama se propaga desta superfície inicial tanto radialmente como Journal of Aerospace Technology and Management

Em MFPL, cuja aplicação requeira elevado desempenho, utiliza-se câmara de empuxo com refrigeração regenerativa, que consiste de uma câmara de parede dupla, com um canal interno, conectadas por meio de um processo especial de soldagem. A parede interna, cujo material normalmente é uma liga de cobre, é usinada em forma de canais longitudinais ou helicoidais para a passagem do líquido de refrigeração e a parede externa em aço inoxidável. Desta forma, o combustível, antes de ser injetado na câmara de combustão, passa por esses canais, retirando o calor do metal em contato com os gases quentes da câmara, reduzindo assim a temperatura da parede interna (Almeida, Shimote, Niwa, 1999). Operacionalmente, cada uma dessas classes de motores apresenta particularidades que os tornam vantajosos ou não, dependendo dos requisitos técnicos do foguete. De uma forma geral, pode-se dizer que o MFPS tem tecnologia de fabricação e integração mais simples, sendo, portanto, mais confiáveis, mas possui menor desempenho que um MFPL. Outras vantagens dos MFPL são: possibilidade de controle do módulo do vetor empuxo e da impulsão total ou do tempo de operação, que podem variar a cada missão e possibilidade de reignição do motor. Existem diversas configurações de projeto de MFPL, em uma delas, somente a câmara de empuxo é mantida em altas pressões (50 até 300 bar) mantendo os tanque a baixas pressões (1,5 a 2 bar) o que reflete diretamente na redução da massa estrutural do foguete (Fig. 1). Neste tipo de MFPL há a necessidade de inclusão de um sistema de turbobomba e gerador de gás para alimentação da câmara de empuxo. Porém, a inclusão deste sistema implica em aumento da complexidade e maior V. 1, n. 1, Jan. - Jun. 2009

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probabilidade de falha. Além disso, pesquisas em diversas áreas do conhecimento devem ser realizadas com o objetivo de estudar os fenômenos físicos e químicos que ocorrem no escoamento desde os tanques até a saída da tubeira. Isso exige uma equipe de engenheiros e pesquisadores altamente especializada, associada a uma estrutura de bancos de testes de pesquisa para verificação dos processos. As validações das simulações computacionais de métodos numéricos e analíticos utilizados podem ajudar na compreensão destes processos (Santana, 2005).

Atividades Espaciais (PNAE), a fim de possibilitar o desenvolvimento de lançadores de satélites com melhor desempenho e precisão (PNAE, 2005). No campo espacial, o IAE tem procurado capacitar recursos humanos para acompanhar o progresso nesse setor. O Instituto Tecnológico de Aeronáutica ITA, o Moscow Aviation Institute - MAI e a Fundação Casimiro Montenegro Filho FCMF surgiram então como parceiros naturais dessa empreitada. Este esforço resultou num curso de Mestrado Profissionalizante com foco em projeto de MFPL, estando em andamento as terceira e quarta turmas. Ao ITA cabe a coordenação do curso e à FCMF, a execução do apoio técnico. O curso é ministrado por professores do MAI, com aulas teóricas e projetos no ITA e trabalhos de laboratório no MAI. As orientações das dissertações ficam a cargo de professores do ITA e pesquisadores do IAE. Deve-se mencionar, ainda, que está em preparação um novo curso para início em 2010, que diferentemente dos anteriores, terá como foco veículos e estágios de foguetes equipados com MFPL. Este convênio já tem produzido algum benefício, pois os recursos humanos formados já estão atuando na área, aumentando desta forma a capacidade de especificar, projetar, fabricar, ensaiar e integrar sistemas complexos propulsivos. Poucos países conseguiram alcançar o domínio da tecnologia de desenvolvimento de MFPL líquido até o presente momento, dentre os quais os de maior relevância são: Estados Unidos, Rússia, França, China, Índia e Japão. Na Rússia, uma das mais importantes universidades voltada para a formação e especialização de engenheiros para a área espacial é o MAI, notadamente pela cooperação entre três de suas faculdades, as quais são voltadas para as áreas de construção de foguetes, motores e sistemas de controle.

Figura 1: Esquema funcional de um MFPL acionado por turbobomba.

Para atuar neste novo cenário, a Divisão de Propulsão Espacial foi idealizada para organizar, planejar, coordenar, executar e controlar as atividades de desenvolvimento de motores-foguetes a propelente líquido, servindo como um vetor para implantar as mudanças necessárias (Barbosa, 2006).

Dedicada ao ensino da tecnologia de motores para aviões e foguetes, a Faculdade de Motores foi responsável pela formação e especialização de várias gerações de engenheiros de MFPL para o programa espacial russo, graças ao corpo docente e instalações laboratoriais de excelência. Por estas razões, a participação de especialistas brasileiros em programa de treinamento com professores do MAI está sendo uma oportunidade ímpar.

Formação de recursos humanos

O curso é desenvolvido em duas fases. A primeira, com duração de um ano, nas instalações do ITA, num total de 800 horas. Todas as disciplinas contam com material didático elaborado pelos professores do MAI. Esta fase contempla ainda, 15 práticas laboratoriais nas instalações do MAI.

O domínio da tecnologia para projeto, fabricação, testes e operação de motores-foguetes a propelente líquido é uma meta a ser alcançada dentro do Programa Nacional de

A segunda fase, também com duração de um ano, é realizada nas instalações do IAE e é dedicada ao desenvolvimento das dissertações em assuntos de interesse,

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na área de MFPL, com consultoria dos professores do MAI e sob orientação dos professores do ITA e pesquisadores do IAE.

- A utilização matérias-primas e propelentes de fácil aquisição, disponíveis no país, principalmente pelo fato de que há de se executar uma grande quantidade de ensaios;

Atividades

- O aproveitamento a capacidade instalada no IAE, já pronta, para ensaiar o motor ora em desenvolvimento, minimizando, assim, os custos decorrentes de obras e construção de instalações.

O IAE tem como missão desenvolver atividades de pesquisa e desenvolvimento no campo aeroespacial, com ênfase nas áreas de materiais, foguetes de sondagem, sistemas de defesa, sistemas aeronáuticos, ciências atmosféricas e ensaios de componentes aeroespaciais (RICA 21-93). A Divisão de Propulsão Espacial (APE) do IAE tem por atribuições: organizar, planejar, coordenar, executar e controlar as atividades de P&D na área de propulsão espacial, a fim de assegurar competência para especificar, projetar, fabricar, integrar e testar motores-foguetes e componentes do sistema de controle do vetor empuxo destinados a equipar veículos lançadores de satélites e foguetes de sondagem, em atendimento aos programas de interesse do Comando da Aeronáutica. Como resultado das atividades da APE, diversos projetos estão em andamento e, para que os projetos desenvolvidos possam ser avaliados e aprimorados, diversos bancos de ensaios estão sendo projetados e construídos. Projetos Atualmente, os projetos em desenvolvimento no IAE são os seguintes: 

Motor-Foguete L5

O MFPL L5 de 5 kN de empuxo (Fig. 2) foi projetado com a finalidade de substituir o atual propulsor do quarto estágio do VLS-1, a propelente sólido, em um veículo “hipotético” denominado VLS-L4, cujos três primeiros estágios seriam idênticos ao do atual veículo lançador de satélites VLS-1. O nível de empuxo deste motor foi definido por otimização, levando-se em conta as características da missão do VLSL4, ou seja, fazer a inserção direta de cargas-úteis de até 427 kg em órbitas polares circulares e com 200 km de altitude (Sikharulidze et al., 2001). A partir da especificação da missão, também foram definidos outros parâmetros propulsivos, tais como tempo de operação e impulsão total. A Tabela 1 apresenta as principais características deste motor. O projeto L5 está permitindo desenvolver a tecnologia de propulsão líquida, levando em consideração: - As limitações tecnológicas existentes no Brasil e a perspectiva de se produzir motores de maior porte; - O emprego de propelentes não agressivos ao meio ambiente, ou que apresentem baixo grau de toxicidade ou baixo risco a segurança durante o manuseio e ensaios; Journal of Aerospace Technology and Management

Figura 2: MFPL L5. Tabela 1: Características principais do MFPL L5

Características Empuxo no vácuo

5 kN

Propelentes

Querosene/LOX

Sistema alimentação

Pressurizado

Pressão de câmara

10 bar

Fluxo de massa

1,62 kg/s

Razão de mistura O/F

1,86

Impulso específico

314 s

Velocidade característica

1760 m/s

Razão de expansão de áreas

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Motor-Foguete L15



O L15 (Fig. 3) é um motor foguete que utiliza propelentes líquidos com alimentação da câmara por meio de pressurização direta dos tanques. Tem como especificação funcional gerar empuxo de 15 kN ao nível do mar para aplicação no foguete de sondagem VS-15. O desenvolvimento desse motor é uma parceria entre IAE e a empresa Orbital Engenharia, com recursos orçamentários da FINEP, Orbital e AEB. O diferencial em relação ao motor L5 é a utilização do sistema de refrigeração regenerativa que tem como principal desafio tecnológico a usinagem dos canais de refrigeração e brasagem do invólucro externo da câmara de empuxo que garantirá a passagem do líquido de refrigeração.

Motor Foguete L75

O L75 (Fig. 4) é um motor foguete com alimentação da câmara por meio de turbobomba que utilizará propelentes líquidos. Tem como especificação funcional gerar empuxo de 75 kN no vácuo para uso em estágio superior de um veículo lançador de satélite. A Tabela 3 apresenta as principais características deste motor foguete.

Figura 3: MFPL L15.

Este motor foi projetado para operar com álcool etílico e oxigênio líquido e, pelo fato da alimentação da câmara ser obtida por pressurização dos tanques de propelentes, a pressão de operação da câmara de combustão é relativamente baixa, comparado com motores com alimentação por meio de turbobomba. A Tabela 2 apresenta as principais características deste motor.

Figura 4: MFPL L75. Tabela 3: Características principais do MFPL L75.

Tabela 2: Características principais do MFPL L15. Características

Características

Empuxo no vácuo

75 kN

Propelentes

Querosene/LOX

Sistema alimentação

Turbobomba

Pressão de câmara

70 bar

Fluxo de massa

23,3 kg/s

Razão de mistura O/F

2,16

240 s

Impulso específico no vácuo

328 s

Velocidade característica

1421 m/s

Velocidade característica

1740 m/s

Razão de expansão de áreas

4,8

Razão de expansão de áreas

Empuxo no vácuo

15 kN

Propelentes

Álcool/LOX

Pressão de câmara

16,5 bar

Sistema alimentação

Pressurizado

Fluxo de massa

6,37 kg/s

Razão de mistura O/F

1,58

Impulso específico

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O principal objetivo a ser alcançado durante o desenvolvimento deste motor será a capacitação, tanto de engenheiros e empresas, para projetar, fabricar e testar os diversos componentes do L75. Os principais desafios estão no projeto e fabricação da câmara de empuxo, da turbobomba, do gerador de gás e do sistema de controle e também a integração destes quatro subsistemas complexos. Para atingir este objetivo foi firmado um convênio entre IAE e EMGEPRON (Empresa Gerencial de Projetos Navais), estatal subordinada ao Comando da Marinha e com recursos provenientes da AEB para concepção, projeto, fabricação, montagem e testes do MFPL L75.

os futuros bancos de testes de maior porte.

Durante a vigência deste convênio, as atribuições do IAE serão o planejamento, a coordenação, o controle das atividades técnicas e o estabelecimento dos objetivos de cada etapa. A EMGEPRON tem como atribuições, o planejamento, a coordenação, o controle das atividades administrativas e a execução de tarefas de seleção de fornecedores, licitação, contratação, aquisição e disponibilização de materiais e serviços. Infra-estrutura O IAE dispõe, atualmente, de bancos de testes tanto para pesquisa quanto para teste de MFPL e seus componentes. São os seguintes os bancos em operação ou em implementação: 

Figura 5: Banco de ensaios a quente de MFPL.

Banco de 1 kN

O Banco de ensaio experimental de motor-foguete a propelente líquido, em fase final de instalação, tem a capacidade de ensaiar motores-foguetes de 1 kN de empuxo e opera com oxigênio gasoso (GOX) e álcool etílico, é constituído de sistema para medição de empuxo, controle e aquisição de dados e de sistema de refrigeração do motor com água. A ignição do motor é realizada com o ignitor gásdinâmico, desenvolvido no IAE e já disponível para operação.



Banco Hidráulico

O Banco Hidráulico (Fig. 6), que utiliza água destilada como fluido de trabalho, é uma instalação que tem como objetivo principal a caracterização de componentes de motores-foguetes a propelente líquido.

Este banco de ensaio tem como principal finalidade a formação acadêmica dos alunos do MPEA, treinamento da equipe do laboratório de propulsão líquida e desenvolvimento de pesquisa nas áreas de transferência de calor e mecânica dos fluidos, de grande importância para a propulsão líquida. 

Banco de 20 kN

O Banco de 20 kN (Fig. 5) foi projetado para ensaios de queima de MFPL, de até 20 kN de empuxo que utilizam sistema de alimentação por meio de pressurização dos tanques e LOX/querosene ou LOX/álcool como propelentes e com pressões da câmara de combustão inferiores a 40 bar. Na pressurização dos tanques, é empregado nitrogênio gasoso. Este banco, que atualmente é utilizado para ensaios dos motores L5 e L15, é pioneiro no IAE e servirá de base para Journal of Aerospace Technology and Management

Figura 6: Banco de ensaios a frio para caracterização de componentes.

O banco é constituído basicamente da área de ensaio dos corpos de prova, do sistema de acionamento composto por bombas e motores elétricos, tanque de armazenamento de água destilada, sistema de filtragem, sistema de V. 1, n. 1, Jan. - Jun. 2009

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arrefecimento de água e pelo sistema de controle e aquisição de dados. A área de ensaio é o local onde serão instalados e realizados os ensaios dos componentes do motor. É composto por um tanque de 2000 litros em aço inoxidável dotado de três tomadas de ensaio onde são feitas as conexões de alimentação e descarga dos corpos de provas através de juntas flangeadas.

O banco permitirá também a investigação experimental nas áreas de propulsão, transferência de calor, instabilidade de combustão, interação combustão-turbulência, interação entre injetores com combustão, ignição e controle ativo e passivo de instabilidade de combustão.

PERSPECTIVAS FUTURAS Características:



Vazão: até 30 kg/s; Pressão normal de trabalho: 35 bar; Pressão máxima: 70 bar que corresponde à pressão máxima fornecida pela bomba centrífuga, conhecida como pressão de “shut off” (quando a vazão é nula); Pressurização por bomba centrífuga multiestágios acionada por motor elétrico controlado por variador de freqüência. Potência: 180 HP (132kW) na condição de pressão e vazão máximas; Vazão: será controlada pela rotação da bomba juntamente com uma válvula de controle instalada na linha; Capacidade do tanque de armazenamento de água destilada: 5m³. Banco de ensaio para estudo de instabilidade de combustão

Este banco de teste (Fig. 7) está sendo desenvolvido para simular experimentalmente uma câmara de combustão de motor foguete a propelente líquido, com o objetivo de investigar a interação combustão-turbulência e seus efeitos na instabilidade de combustão, bem como estudar a validade dos modelos de cinética química adotados para os propelentes considerados.

Qualquer abordagem para o desenvolvimento de MFPL deve levar em consideração que a complexidade dos seus sistemas aumenta na medida em que se aumenta seu desempenho. Sistemas simples, como os pressurizados, não são utilizados em estágios inferiores pelo fato de que todo o sistema está submetido a altas pressões, tendo como conseqüência um aumento significativo da massa estrutural do foguete o que reduz sua eficiência. No entanto, são utilizados em sistemas de controle de atitude do foguete, em que o requisito desempenho é colocado em segundo plano priorizando-se neste caso a confiabilidade e a simplicidade. Em MFPL que utiliza turbobomba a complexidade aumenta e com ela a eficiência do sistema. Neste caso a parte pressurizada se restringe ao trecho entre a saída das bombas até a câmara de empuxo o que reduz a massa estrutural dos tanques de propelentes, que estão a baixas pressões, e permite a utilização de pressões de câmara mais elevadas. Como o impulso específico aumenta com a pressão na câmara o desempenho do foguete também se eleva. Estes dois tipos de MFPL já estão sendo desenvolvidos no IAE, quais sejam, o L5 e o L15 que têm pressurização dos tanques, e o L75 com turbobomba de ciclo aberto, e servirão de base para os futuros desafios. Estudos de MFPL de ciclo aberto utilizando etanol e LOX estão em elaboração com fins comparativos e cujos resultados deverão ser discutidos com vistas à uma possível aplicação deste propelente em futuros projetos.

CONCLUSÃO Foram apresentados, neste artigo, os trabalhos que estão em andamento no IAE e algumas sugestões para desenvolvimento da tecnologia de propulsão líquida no Brasil, considerando a experiência de países que já ultrapassaram esta fase inicial e foram bem sucedidos. As primeiras ações neste sentido foram iniciadas na década de 90 com a formação de recursos humanos e parcerias com instituições de países detentores do conhecimento e, posteriormente, a nacionalização desta tecnologia utilizando os recursos humanos formados por meio de programas de especialização. A transferência gradual dos conhecimentos até a completa independência tanto em projeto, fabricação ou testes, deve ser a meta a ser seguida. Figura 7: Banco para estudo de instabilidade de combustão. Journal of Aerospace Technology and Management

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necessitarão ser incrementados nos próximos anos, fazem parte da estratégia de desenvolvimento próprio (no Brasil) de motores-foguetes e devem estar alinhada com as estratégias dos órgãos governamentais, devido ao fato que a via alternativa, ou seja, a compra dos motores- foguetes no exterior, poder causar a descontinuidade do programa espacial para lançamentos de satélites em caso de embargos econômicos e tecnológicos.

REFERÊNCIAS Almeida, D. S., Shimote, W. K., Niwa, M., 1999, “Selection of Materials for Combustion Chamber of Liquid Propellant Rocket Engine”. 15º Congresso Brasileiro de Engenharia Mecânica, COBEM, Águas de Lindóia, Brazil. Barbosa, F. I. et al., 2006, “Proposta para a Criação da Divisão de Propulsão Espacial”, IAE, São José dos Campos, Brazil. (Relatório Técnico). Oliveira, U.C., 2008, “Motores-Foguete dos Veículos Nacionais”. 5º Congresso Nacional de ENGENHARIA Mecânica, CONEM, Bahia, Brazil. PNAE, 2005, “Programa Nacional de Atividades Espaciais 2005-2014: AEB - Agência Espacial Brasileira”, Ministério da Ciência e Tecnologia, Brasília, Brazil. RICA 21-93, 2007, “Regimento Interno do Instituto de Aeronáutica e Espaço”, IAE, São José dos Campos, Brazil. Santana Jr., A., 2005, “Proposta de Plano de Trabalho para 2006-2007”, IAE, São José dos Campos. (Relatório Técnico 010-100000/A0002). Sikharulidze, Y., Barbosa, F. I., Pereira, F. C. V., Tamashiro, R. Y., 2001, “Ballistic Analysis of VLS-1 Modification by the Use of Liquid-Propellant Rocket Engine”. IAE, São José dos Campos (Relatório Técnico 007/ASE/01).

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Alberto W. S. Mello Junior* Institute of Aeronautics and Space São José dos Campos - Brazil amello@iae.cta.br

Abílio Neves Garcia Institute of Aeronautics and Space São José dos Campos - Brazil abiliogarcia@iae.cta.br

Ribeiro Fabrício N. Institute of Aeronautics and Space São José dos Campos - Brazil fabricio@iae.cta.br

Daniel Ferreira V. Mattos Institute of Aeronautics and Space São José dos Campos - Brazil daniel.ferreira@iae.cta.br

*author for correspondence

Brazilian Air Force aircraft structural integrity program: An overview Abstract: This paper presents an overview of the activities developed by the Structural Integrity Group at the Institute of Aeronautics and Space - IAE, Brazil, as well as the status of ongoing work related to the life extension program for aircraft operated by the Brazilian Air Force BAF. The first BAF-operated airplane to undergo a DTA-based life extension was the F-5 fighter, in the mid 1990s. From 1998 to 2001, BAF worked on a life extension project for the BAF AT26 Xavante trainer. All analysis and tests were performed at IAE. The fatigue critical locations (FCLs) were presumed based upon structural design and maintenance data and also from exchange of technical information with other users of the airplane around the world. Following that work, BAF started in 2002 the extension of the operational life of the BAF T-25 “Universal”. The T-25 is the basic training airplane used by AFA - The Brazilian Air Force Academy. This airplane was also designed under the “safe-life” concept. As the T-25 fleet approached its service life limit, the Brazilian Air Force was questioning whether it could be kept in flight safely. The answer came through an extensive Damage Tolerance Analysis (DTA) program, briefly described in this paper. The current work on aircraft structural integrity is being performed for the BAF F-5 E/F that underwent an avionics and weapons system upgrade. Along with the increase in weight, new configurations and mission profiles were established. Again, a DTA program was proposed to be carried out in order to establish the reliability of the upgraded F-5 fleet. As a result of all the work described, the BAF has not reported any accident due to structural failure on aircraft submitted to Damage Tolerance Analysis. Key words: Fatigue, Damage tolerance, Structure, Service life.

INTRODUCTION The first Brazilian flight was reported on 23 October 1906, and was performed by Alberto Santos Dumont in an airplane named 14 bis. At that time, not much was known about other achievements, so that initially Santos was considered to be the first man to fly a fixed-wing craft, capable of taking off, flying and landing under its own power (Hoffman, 2003). Another important milestone in Brazilian aeronautics was the flight of the Demoiselle (Fig. 1). It was the first ultra-light airplane in history (Winter, 1998). Santos Dumont flew the Demoiselle for the first time in 1908.

article needed to be tested to prove its fatigue strength. The safe life approach is based on the life-to-failure test divided by a scatter factor, usually three or four, to account for uncertainties in material properties, manufacturing and assembly processes, and applied loads. When strictly enforced, the safe life approach imposed a severe penalty: if the service life was reached, then the fatigue life was deemed expended and the aircraft removed from service. However, if a flaw existed in the structure, the safe life did not ensure flight safety.

Airplanes manufactured in the first half of the 20th century were primarily based on the static strength point of view. The aircraft industry's approach to achieving structural integrity was significantly modified as a result of failures that occurred in the 1940s and 1950s. The most significant were the fatigue failure of the wing of the Martin 202, in 1948, and the Comet fuselage failures that occurred in 1954. At that time, the concept known as safe life was introduced. According to this philosophy, an ________________________________ Received: 05/05/09 Accepted: 20/05/09 Journal of Aerospace Technology and Management

Figure 1: Demoiselle Santos Dumont's first ultra-light plane 1908 (Winter, 1998) V. 1, n. 1, Jan. - Jun. 2009

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Another significant change in the structural integrity program was due to the failure of an F-111, in 1969. This and other accidents initiated the era of damage tolerance for military aircraft. In this methodology, flaws are assumed to exist in a structure's most critical locations. The goal of the structure integrity program is to find and repair the damage before failure occurs. This new approach was also adopted by the FAA (Federal Aeronautics Administration) in 1978, due to fatigue concerns relating to a catastrophic Boeing 707 failure. Ever since the first flight, Aeronautics in Brazil has developed with the aim of better and safer flying. Capability and confidence in structural tests and analysis were always the main goal in the Brazilian Air Force (BAF). Until 1990, the fatigue life philosophy adopted by BAF was the safe life. After in-depth studies and field experience, it was concluded that Damage Tolerance Analysis (DTA) was a much more reliable concept for determining the service life of aeronautical systems. The main steps of a DTA Program can be summarized as follow: 

Flight data survey

This task is necessary in order to obtain the information on how the airplane is being used. Some data must be available for further analysis: load factors, altitude, speed, angular accelerations, etc. This body of information is called L/ESS (Load/Environment Spectra Survey) 

as inspections on it are properly performed. The first Brazilian aircraft to undergo a DTA-based life extension was the F-5, in the mid-1990s. Southwest Research Institute (SwRI) was contracted through the USAF (United States Air Force) to perform the analysis (Wieland et al., 1996). Their work included hands-on job training for BAF personnel. The load spectrum was obtained from 5 F5-Es operating at the Santa Cruz Air Force Base, Brazil. In the late 1990s, a group was formed at the Institute of Aeronautics and Space (IAE) with the objective of developing human resources and technical expertise for inhouse damage tolerance analysis. This group is now part of the Structural Integrity Subdivision (ASA-I) at the Aeronautical System Division (ASA) at the IAE. The first in-house DTA work was with the BAF AT-26 “Xavante”. This aircraft was originally designed under a safe-life structural concept. It is a light ground-attack, reconnaissance and training subsonic jet aircraft. It was produced by EMBRAER under license from the Italian manufacturer Aermacchi SpA. The first plane flew in 1971. More recently, in the mid-90s, 4 accidents were reported two with BAF airplanes and 2 others worldwide involving this type of aircraft. All of them were related to structural failure in the wing spar (Fig. 2). Subsequent analysis showed that the failure was due to manufacturing quality problems caused by improperly drilled holes in a critical area (Mello Jr, 1999).

Stress-to-load Ratio

This is how the stress in each Fatigue Critical Location (FCL) relates to the L/ESS. The equations come from stress analysis and strain gauged aircraft. 

Stress Spectra

For each FCL the stress spectra are determined, based on the L/ESS and the stress-to-load ratio. 

Residual Strength

Based on the material properties, structure geometry and fracture mechanics parameters, how the structural strength decreases with crack size is determined. The minimum strength required defines the critical crack siz 

Crack growth curve

With all previous parameters and a valid code, the crack growth can be computed and inspection intervals may be assigned according to the capability of the maintenance depot. The damage tolerance approach provides a framework for extending structural life. Because structural repairs and replacements are based on periodic inspections determined by analysis and testing, an aircraft is permitted to fly so long Journal of Aerospace Technology and Management

Figure 2: AT-26 wing main spar failure (Mello Jr., 1999).

Following this work, the BAF Structural Integrity Group was also responsible for performing the DTA for the T-25 “Universal” trainer, finished in 2005. Currently, the focus is on the upgraded F-5EM/FM, as discussed in the following sections. THE MOST RECENT STRUCTURAL INTEGRITY PROGRAM 

AT-26 (EMB 326) DTA

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Structural Integrity Subdivision began DTA assessment on the AT-26. The main requirements were to have a more reliable structure as well as to keep the flying status beyond the original, and proven unsafe, service life. The main tasks for the AT-26 DTA were: data review, flight data recording, processing and evaluation, strain gauged airplane for flight test campaign, coupon tests, structural FEM (Finite Element Modeling) and fracture mechanics analysis, and non-destructive inspection development. Figure 3 shows several pictures representing tasks accomplished during the AT-26 DTA.

Figure 4: Development in laboratory (a) and in the field (b) of the eddy current inspection guided by a video probe (Garcia et al., 2001).



Figure 3: Pictures of the tasks relating to the AT-26 DTA.

The operational data and maintenance feedback were obtained from the Air Squadrons and PAMARF (BAF Depot responsible for this fleet), respectively. The fatigue critical locations (FCLs) were presumed based upon structural design and maintenance data and also from exchange of technical information with other users of the airplane around the world. The operational usage was obtained from actual missions of five fighters flying at the 1º/4º Grupo de Aviação de Caça in Fortaleza over a period of one year. The load/environment spectra survey (L/ESS) was used to determine the external forces acting on the aircraft components. Finite element models of selected FCLs were constructed in order to obtain the stress levels at the locations most likely to develop fatigue cracks (Mello Jr., 1999). These local stress levels were experimentally confirmed and adjusted through an extensive flight test program. Strain gauges were installed at the main aircraft FCLs for stressto-load ratio validation. Retardation parameters from coupon tests were then used as input for the crack growth analysis to obtain the crack growth curves (Mello Jr., 1998) and to define the adequate intervals for the non-destructive inspection method (NDI) applicable for each FCL. A total of 15 fatigue critical locations were analyzed and for each one a proper NDI was scheduled. For the wing spar, considered the most critical spot, a new NDI procedure had to be implemented. The critical region and surroundings are inspected by eddy current technique with the help of video pack equipment (Fig. 4). This inspection is backed up by XRay of the entire region.

T-25 “Universal” life extension

The T-25 is the basic training airplane made by the Brazilian Aviation Company NEIVA, and used by AFA - the Brazilian Air Force Academy. This airplane was also designed under the safe-life concept. As the T-25 fleet approached its service life limit, the Brazilian Air Force began to question whether it could be kept flying safely. The answer was provided by an extensive Damage Tolerance Analysis. This airplane entered service at the beginning of the 70s. Unlike the previous project, no catastrophic structural accident was reported during its service life. Additionally, the safe-life full scale test was stopped after 7,000 effective flight hours without any reported major damage. The main goal was to extend the T-25 service life by 5,000 flight hours, retaining the integrity of the structure. For the complete analysis, the same steps presented for the AT-26 were followed. A total of 25 fatigue critical locations were considered: 11 in the wing, 10 in the fuselage, 3 in the horizontal stabilizer and 1 in the vertical stabilizer (Mello Jr. et al., 2004). Over 700 flight hours were collected from the BAF Academy planes, covering all the missions and typical idiosyncrasies of a variety of trainee pilots. For proper calibration of the stress-to-load ratio equations, 16 FCLs were strain gauged and a test flight campaign was conducted. The DTA included an interactive phase with the Maintenance Depot and End User. This was considered a key step for the final result, since all the changes and recommendations must be maintainable and operational. Among the suggested changes in maintenance procedure were the new inspections in the center box wing spar and in the attachment lug region of the external/internal wing. Strap reinforcement at the root wing lower spar cap was also proposed to be carried out during a major Depot overhaul (Mello Jr. et al., 2005).

F-5M STRUCTURAL INTEGRITY PROGRAM The main achievement of this project was to give the Brazilian Air Force the necessary time to transition from this aircraft to its replacement and increase the structural reliability of the AT-26. Journal of Aerospace Technology and Management

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the new system in a more capable aircraft. Also, the weight and its distribution have been modified. All of this made a new structural analysis mandatory to ensure a reliable service life. A complete proposal for a 2-year DTA program was submitted to the Brazilian Air Command. The program started on August 2007. The fleet is now referred to as F-5EM/FM. Among the various changes that affect the structural life is the cutting of the forward fuselage at station 103 (60.5 for F-5F) to include a bigger radar antenna and the removal of one gun. This was necessary to make room for the new avionics. After all the modifications during the upgrade process, the “new” aircraft increased in weight, leading to changes in the structural load distribution. Also, new configurations and mission profiles were established. One example of this configuration/profile change is the new airplane's capability to perform ripple, having the CCRP (Continuous Computer Release Point). An extensive gjump in flight campaign was carried out to certify this type of mission as safe for the F-5. Strain gauges and accelerometers were installed to measure the instant load at critical spots. With the new avionics, all airplanes are eligible for L/ESS (Load/Environment Spectra Survey). At the end, the DTA will determine what will be the impact of the upgrade on the maintenance schedule and workforce to support the F5EM/FM fleet. Also, it will show how new avionics and weapons systems affect the usage of the same platform in a specific Squadron. Due to changes in weight and balance, comparisons are being made between stress spectrum profiles for some of the aircraft fatigue critical locations. Finally, a maintenance schedule will be proposed based on what the analysis predicts. So far, more than 700 flight hours have been collected from the BAF F-5 Squadrons. Several computer codes and pre-analyses have been written, in order to substantiate the upcoming F-5EM/FM DTA Final Report. PROSPECTIVE WORK The Brazilian Air Force is already anticipating the need for a life extension of the A-1 “AMX”. The AMX is an attack jet that provides the required performance to acquaint pilots with the demands of modern combat scenarios. The complete structural reassessment will be performed after a mid-life avionics upgrade to be carried out over the next few years. The A-29 “Super-Tucano” (Fig. 5) is a combination of a turboprop with fourth-generation avionics and armament systems. The Super-Tucano has an outstanding humanmachine interface, fully compatible NVG Gen III cockpit lighting innovation. It can operate in the most hostile environments and from unprepared runways, by day or Journal of Aerospace Technology and Management

night. Its first flight for the BAF was on August 2004. The BAF requirements included a comprehensive fatigue life evaluation, following all the structural integrity and reliability certifications. EMBRAER has contracted the IAE's Structures Laboratory to perform the durability and damage tolerance full scale fatigue test for this aircraft. A three service life time has been simulated, and now cracks will be induced in the most critical areas. Another two service lives will be tested with monitoring of the induced cracks. The damage tolerance analysis is being performed by EMBRAER.

Figure 5: A-29 Super-Tucano Flying over the coast (a), assembled for fatigue full scale test (b). There are several other projects that may be implemented over the next few years by the IAE Structural Integrity Group. Among them are C-130 DTA update, T-27 “Tucano” DTA and A-4 (Brazilian NAVY) DTA assessment. CONCLUSION Brazilian aviation has a history that is deeply involved in the history of manned flight. Since 1906, Brazil has been very active in the efforts to make flying better and safer. The new concepts of DTA to assure structure integrity were adopted by the BAF in the 1990s and since then there has been a significant improvement in safety for the projects that adopted that philosophy, with no reported accident due to structural failures on aircraft subjected to DTA. The IAE has proven that it has the necessary tools and technical personnel needed to analyze, propose changes and perform the follow-up for any structural problem faced by the Brazilian Air Force. New operational requirements from the BAF will provide a long-term demand for human resources involved in structural analysis and design from the IAE Aeronautical Systems Division, Structural Integrity Group. ACKNOWLEDGMENTS The Authors would like to thank the Brazilian Air Command for having sponsored the Structural Integrity Group, always providing the necessary means to carry out the service. V. 1, n. 1, Jan. - Jun. 2009

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REFERENCES Garcia, A. N. et al., 2001, “Resultados Finais da Análise de Tolerância ao Dano das Aeronaves AT-26 Xavante da FAB”, IAE, (ASA-G 02/01). Hoffman, P., 2003, “Wings of Madness: Alberto SantosDumont and the Invention of Flight”, New York, NY. Theia, pp. 259. Mello Jr., A. W. S., 1998, “Crack 2000 Program: Software for Practical Fracture Mechanics and Damage Tolerance Analysis”, User's Manual. CTA, São José dos Campos. Mello Jr., A. W. S., 1999, “Definição dos Pontos Críticos em Fadiga da Aeronave AT-26 Xavante da FAB, e Seus Parâmetros de Inspeção”, IAE, São José dos Campos (ASA-G 01/99) Mello Jr., A . W. S. et al., 2004, “Determinação das Funções de Transferência para os Pontos Críticos das Aeronave T-25”, São José dos Campos (ASA-G 13/04). Mello Jr., A. W. S. et al., 2005, “Análise de Tolerância ao Dano das Aeronaves T-25”, São José dos Campos (ASA-G 08/05) Wieland, D. H. et al., 1996, “F-5 FMS Durability and Damage Tolerance Update Revised Final Report F-5E Brazilian Air Force”, SwRI Project number 06-4222. (SwRI 5020B-E, CDRL 5020B-E), San Antonio. Winter, N., 1998, “Man Flies: The Story of Alberto SantosDumont, Master of the Balloon, Conqueror of the Air”, Hopewell, NJ, Ecco Press, pp. 121.

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Daniel Ferreira V. Mattos* Institute of Aeronautics and Space São José dos Campos - Brazil daniel.ferreira@iae.cta.br

Alberto W. S. Mello Junior Institute of Aeronautics and Space São José dos Campos - Brazil amello@iae.cta.br

Fabrício N. Ribeiro Institute of Aeronautics and Space São José dos Campos - Brazil fabricio@iae.cta.br

*author for correspondence

F-5M DTA Program Abstract: The Brazilian F-5 was submitted to avionics and weapons upgrade. This “new” aircraft has proven to be heavier and more capable. A comprehensive damage tolerance analysis is being performed to evaluate how the new mission profiles and weight distribution may affect the airframe structural integrity. Operational data were collected at the Brazilian Air Force Bases where the fighter is flown. Software was developed in order to acquire, filter and analyze flight data. This data was used for comparison between the pre and post modernization mission profiles and to determine the stress level in each of the known aircraft fatigue critical locations (FCL). The results show that the change in aircraft weight and balance and the new operational profile can significantly change the inspection intervals of certain fatigue critical locations of the structure. A preliminary result for the horizontal tail has shown that this component will have a much more restrictive maintenance schedule to assure flight safety. Key words: Fatigue, Damage tolerance, Structure, F-5, Flight data analysis, Crack growth.

LIST OF SYMBOLS BACO BASC FAB DTA FCL FDR IAE Ny Nz NDI RFC USAF SwRI

Canoas Air Force Base Santa Cruz Air Force Base Brazilian Air Force Damage Tolerance Analysis Fatigue Critical Location Flight Data Recorder Institute of Aeronautics and Space Lateral load factor Normal load factor Non Destructive Inspection Representative Flight Condition United States Air Force Southwest Research Institute

high-g maneuvers the most significant contribution that define their service life. A structure can lead to catastrophic failure even if it is submitted to loads smaller than its structural design limit. This is a cumulative effect, known as fatigue. Figure 1 illustrates the basic mechanism of how cyclic loads may induce a structural failure.

INTRODUCTION The development of new technology and declining governmental budget make it difficult to replace military fleet as it becomes obsolete. Therefore, Air Forces around the world have alternatively decided to update the existing vectors in their inventory. The military aircraft modernization primarily aims at extending mission profiles, but also changes considerably the structure weight and balance. The main effect is the increase in stress levels, which can therefore compromise the structural integrity. To assure flight safety, a comprehensive campaign to collect operational data and to analyze the impact in the structural integrity of the aircraft is necessary.

The aircraft structure is subject to cyclic loads due to maneuvers and gusts that overlap stationary loads of a steady flight. Aircraft fighters, as the F-5, have from the ____________________________________ Received:05/05/09 Accepted:27/05/09 Journal of Aerospace Technology and Management

Figure 1: The basic mechanism of fatigue (Mattos, 2008).

As already mentioned, the most compelling reason to extend an aircraft's structural life is the pressure to save money. Figure 2 shows the cost of a combat aircraft in U.S. dollars. As can be seen, the cost has increased exponentially over the years. On the other hand, any weapon system and avionics modernization is also costly. Therefore, modernization usually requires a reassessment of the airframe and further extension of its service life. V. 1, n. 1, Jan. - Jun. 2009

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the Load/Spectra Environment Survey (L/ESS). This type of survey takes into account not only the load factor, as conducted in traditional analyses, but also addresses the aircraft mission profiles, operational environment, speed, altitude and other time dependent parameters. table 1 illustrates an example of how the same load factor may result in different stress levels depending on the maneuver condition. The example is presented for the F-5 Dorsal Longeron, for the normal load factor (Nz) of 5g's and Mach 0.8. The calculated stress varies up to 47% with changes in weight, flap deflection and altitude. Table 1: F-5M Dorsal Longeron Stress Case 1 2 3 4

Figure 2: Aircraft average unit cost per year (Burnside, 1993).

The Brazilian Air Force (FAB) is also part of these worldwide budget restrictions. For this reason, until FAB is able to properly acquire new fighters, it is necessary to upgrade and keep the existing ones flying. As part of this, the implementation of airframe life extension and the guarantee of the structural integrity are vitally important. The F-5 fleet was one of the elected FAB vectors to have its service life extended and the avionics upgraded. In order to fit all new equipment, some structural modification was implemented. With new avionics integration, the F-5 basic weight has increased. Additionally, the F-5 has extended its operational capability, which generates a more severe load spectrum. Figure 3 depicts how an increase in spectrum severity may impact the range of non destructive inspection interval. To properly account all this changes, a comprehensive damage tolerance analysis was necessary, which is described in the next section.

Weight (lb) 12797 12797 11917 11917

Fuel Weight Flap Alt. Def. (°/°) (ft) (lb) 0/0 2200 15000 12/8 2200 15000 12/8 1320 30000 12/8 5000 1320

Stress (ksi) 14.16 19.40 16.14 20.78

Comparing case 1 and case 2, the single change in flap position leads to an increase of 37% in stress, and for cases 3 and 4, changing altitude and keeping fixed all other conditions ensued in a 28.7% difference in stress. Analyzing these cases, we can conclude that not only the load factor, but also other parameters are extremely important to properly determine the structure stress level. All the major steps of the F-5M DTA Program are represented by the flowchart shown in Figure 4 and are described in sequence. Data Collection Fatigue Data Selection Data Edition and Pre-Analysis Data Reduction Stress Sequence Crack Growth Analysis Establishment of Inspection Plan Figure 4: DTA Flowchart.

Figure 3: Impact in the range of NDI interval.

THE F-5 DTA PROCESS The damage tolerance analysis (DTA) comprises several steps. The first step is to determine the way the aircraft is operated in each squadron. This step requires performing Journal of Aerospace Technology and Management

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Data Collection:

The data compilation must satisfy the specification content in section 3.2.2 of the Military Standard MILA-8866B. The F-5M Flight Data Recorder (FDR) can store data such as altitude, Mach, speed and load factors. The data is recorded in average frequency of 10Hz and is disposed into XML files. These files are downloaded at the V. 1, n. 1, Jan. - Jun. 2009

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Air Force Bases and are used during flight debriefing. figure 5 shows an example of the data of a XML flight file. The size of total flight files normally exceeds 100 MB.

F5DACOM creates a new file with all the supplementary data. This new file and the XML flight files are sent to the Institute of Aeronautics and Space (IAE) for analysis. Figure 7 illustrates the main tasks in the collection data process. First, the squadrons download the XML files from the FDR and run the F5DACOM software. Then, the files are sent to IAE by mail (DVD) or through the internet (FTP).

Squadrons

F5DACOM

FDR

(Supplementary Data)

(XML Files)

FTP DVD

IAE Figure 7: Data collection methods. â&#x20AC;˘ Figure 5: Part of an XML file from F-5M FDR.

Some relevant information of the flights is not registered by the FDR. Therefore, the XML files must be supplemented to make them useful for the next DTA steps. Computer software (F5DACOM) was developed to include this supplementary data for the flight files (Ribeiro, 2008). This software is used by the Air Force Bases, so that information such as configuration, external stores and events during the flight (weapons launched/released or refueling) are recorded. Figure 6 shows the main screen of the F5DACOM software.

Fatigue Data Selection:

The fatigue data pre-selection consists in applying a filtering process to the original data, in order to keep only the events considered significant for the pre-analysis phase and the remaining DTA process. In order to accomplish this phase, a computer program named SEDAF was developed (Ribeiro, 2009). The SEDAF software performs a filtering process and eliminates unnecessary data by selecting peaks and valleys of the load factors, which are the most important values for the DTA. This procedure reduces the average package of information from 100MB to 300KB through a complex process involving dozens of XML files from the aircraftâ&#x20AC;&#x2122; s data acquisition system. SEDAF uses three triggers to do this: one for normal load factor (Nz), one for lateral load factor (Ny) and another for time. The values of these triggers are 0.5 g, 0.1 g and 30 s for Nz, Ny and time, respectively. These values were based on historical data where it was noticed that variations of Nz smaller than 0.5 g and variations of Ny smaller than 0.1 g did not contribute significantly to the fatigue analysis for this type of aircraft. The software also selects events at every 30 s. Although another filtering will still be performed in the next steps, the amount of remaining data is necessary for flight viewing during the data edition and pre-analysis stages. Figure 8 shows an example of the filtering performed by SEDAF. Red marks are points kept for further analysis.

Figure 6: F5DACOM screenshot (Ribeiro, 2008). Journal of Aerospace Technology and Management

SEDAF continues calculating the weight reduction during the flight caused by events related to weapon systems such as launched missiles, released bombs, released chaffs/flares and the ammunition fired. V. 1, n. 1, Jan. - Jun. 2009

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manufacturer, performed various tests to determine how the configuration and maneuver types affect the airframe structure. To properly define the structural impact during a flight event, the maneuvers are divided into three types: symmetrical, roll and abrupt pitch.

Figure 8: Result from pre-selection for pre-analysis.

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Symmetrical maneuver is characterized by having no significant variation in angles of roll, yaw or pitch. Usually, the lateral load factor (Ny) is very small.

•

Roll maneuver is characterized by its significant variation in roll angle along time and its non-zero value for Ny.

•

Abrupt pitch maneuver is characterized by a wide variation of pitch angle in a short period of time, with no significant change in yaw or roll movement. Such maneuvers have major importance in DTA due to the high impact on the horizontal tail structure.

Data Edition and Pre-Analysis:

The purpose of pre-analysis is setting the data for the next steps of the DTA program. The data must be collected and pre-analyzed according to Military Standard MIL-STD1530, section 5.4.4 and AFWAL-TR-8278, section 5.3.2. The software EPAD F-5M was developed specifically to accomplish this task (Mello Jr., 2008). Each flight, previously filtered by SEDAF, must be edited and preanalyzed by the EPAD F-5M. The information contained in each file can be viewed and edited as a table or graphically. It allows the user to check and fix any discrepancies in all the data. The first step of pre-analysis is to define the flight phases, such as: climb, cruise, primary, cruise, descent and approach. This marking of the flight phases requires some user's experience due to the nuances of each flight mission. EPAD allows two cruise phases, one before and another after the primary. Figure 9 shows an EPAD chart screen, where the flight phases can be seen in the altitude and Nz plots.

During a flight, the aircraft is subjected to different conditions of weight, altitude, Mach, load factors and flap position caused by different maneuvers and events. Based on these conditions, EPAD associates a representative flight condition (RFC) to every point in a flight. These RFCs were previously tested during the Northtrop flight tests campaign, when the loads of the aircraft structure were measured. •

Data Reduction:

The pre-analyzed data generated by EPAD still represents very large amounts of information and most of these are unnecessary for the fatigue life analysis. Thus, it is necessary to identify the most relevant peaks and valleys of Nz. This data reduction process is performed in accordance with MIL-STD-1530 standards, sections 5.4.4.2 and 5.4.4.3, MIL-A-8866B, Section 3.2.2 and manual AFWALTR-823078, Section 5.3.2. These standards define criteria to count cycles, commonly used for fighters and known as conventional counting. The criteria define rules about peaks and valleys, as follows: A peak needs to be: o o

Figure 9: EPAD screenshot.

The flap position is a very important parameter that is not recorded in real time. It is determined by EPAD based on flight conditions for each event (angle of attack and altitude), following the logical procedure described in the aircraft's flight manual. Northrop Corporation, the F-5 Journal of Aerospace Technology and Management

the largest value between two valleys; preceded and followed by valleys whose differences between peak (p) and each valley (vi) are not lower than 50% of peak value less one, i.e.: (1)

greater than 2g, unless the following valley is less or equal to zero. V. 1, n. 1, Jan. - Jun. 2009

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A valley needs to be: o o

the lowest value between two peaks; at least 1g lower than the previous and next peaks.

Figure 10 shows an example of the counting process for a few events.

concentration. F-5M has a total of 41 FCLs: 10 points at the wing, 7 at the fuselage, 2 at the attachment region of the engines, 4 at the vertical tail, 2 at the horizontal tail and 16 at the region called "ziploc". Each FCL has different stress distributions, because they are at different locations of the aircraft, and also involve different materials and geometry. The Northrop flight test campaign determined the loads acting on points distributed over 12 stations, taken in relation to a reference datum. Each FCL is associated with one of these stations. The loads are determined based on the type of maneuver as follow: o

Figure 10: Conventional counting criteria. Figure 11 shows the real flight spectrum of Nz using data reduction process. The remaining points have been plotted in red. As can be seen, at the beginning of the flight, there is a low Nz level which is related to the climb and cruise phases. Each flight event that remains at this stage is registered according to the type of mission, the flight phase in which it occurred, the RFC associated and the aircraft weight. After this step, the full discrete spectrum can be generated, normally representing 1,000 flight hours per type of mission.

Load calculations: Symmetrical

For a given FCL, the associated station has some related symmetrical RFC. Each RFC has 3 listed values of Nz. Each Nz value has the forces and moments measured during flight tests at that station. Thus, the forces and moments for a given Nz referred to that specific FCL and RFC can be calculated through a linear interpolation. o

Roll

The loads due to roll maneuver are calculated in two steps. The first one determines the symmetric loads and the second one calculates the asymmetric loads, caused by rolling events, which will be added to the symmetrical loads. The additional loading caused by the roll maneuver is extracted directly from a table by searching the closest value of Nz. The roll loads are tabulated for a roll rate of 100°/s. To be properly accounted for, the load must be adjusted for the actual maneuver roll rate. o

Abrupt Pitch:

Figure 12 shows a typical time history during abrupt pitch maneuver. There are two instants in time that have relevant importance: the entry part where the maximum down tail load is developed and the check part where the most positive tail load occurs. These points are identified as “Entry” and “Check”.

Figure 11: Result from the counting process. (Mattos, 2008). •

Stress Sequence:

There are points in a structure where the possibility to develope cracks is higher. They are called Fatigue Critical Location (FCL) and generally occur in regions of stress Journal of Aerospace Technology and Management

Figure 12: Typical Abrupt Pitch Maneuver (Northrop, 1977). V. 1, n. 1, Jan. - Jun. 2009

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For each event, Nz “Entry” and “Check” are calculated and compared with Nz valley and peak, respectively. The lower value between Nz “Entry” and valley is chosen and the higher value between Nz “Check” and peak is chosen. Then, the total load is calculated adding abrupt load to the corresponding symmetric load. -

Stress-to-load ratios and stress spectra:

A previous step enabled to know the exact loads acting on a specific region of the airframe, as a maneuver occurs. However, for each FCL it is necessary to know the actual stress the structure is subjected to. These stress-to-load ratios were obtained by static and fatigue tests of instrumented aircrafts and also finite element analysis using the NASTRANTM software. A dedicated computer program was created to generate the stress spectra for each FCL, GCTAF F-5M (Mello Jr., 2009). By using the load spectrum from the counting process and all other parameters, such as maneuver conditions, mission mix, and the stress-to-load rations, the GCTAF software generates a stress spectrum for each FCL that is used by the crack growth analysis software. •

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Establishing an Inspection Plan:

With the information obtained in the residual strength and crack growth curves, the inspection intervals can be established for the referenced FCL, depending on the inspection method chosen. The final work related with DTA is an interactive phase with the Maintenance Depot and End User. The proposed inspection interval may be slightly changed to keep the aircraft maintainable and operational. RESULTS The F-5M DTA Program will be completed in August 2009. The following results are preliminary because only a small amount of data was available at this point. However, they show how changes in weight and mission profiles may impact differently in different FCLs of the F-5M. Figures 14, 15 and 16 depict the stress spectra for fuselage, FCL's wing and stabilizer, respectively.

Crack Growth Analysis:

The next step of a DTA program is to determine how the structure would behave in the presence of cracks. The Crack 2000 software (Mello Jr., 1998) was developed to provide an automated Damage Tolerance Analysis to FAB aircrafts. Its primary capability is to calculate the fatigue life and crack instability of structures subjected to cyclic loading which contain initial flaw defects. The user has to input a spectrum, geometry and material properties, and choose some options like the retardation effect. The output files have all the necessary information for a complete DTA, such as residual strength and crack growth graphics (Fig. 13). The residual strength is the resistance that the structure withholds in presence of a crack, while the crack growth curve shows the time required for the crack to reach its critical size.

Figure 13: Inspection Diagram. Journal of Aerospace Technology and Management

Figure 14: FCL F3o: Edge of Fwd Upper Longeron

The black curves represent the stress spectra for the original F-5E DTA. The red curves were generated by using the new stress-to-load ratios, keeping the original F-5E g-spectrum. The comparison of these two curves shows how the weight and balance changes affect the stress level. The blue and green curves are generated with new stress-to-load ratios and new g-spectrum for the F-5M fleet operating at BACO and BASC, respectively. It can clearly be seen that the “new” aircraft with new operational profile is subjected to higher stress levels, which consequently imply in a more restrictive maintenance schedule. The wing is the component that has minor variation in stress levels, with the new result very close to the original one (fig. 15).

Figure 15: FCL W6: Wing lower skin fastener hole. V. 1, n. 1, Jan. - Jun. 2009

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CONCLUSIONS

Figure 16: FCL H1: Horizontal Tail. As an example of the F-5M upgrade impact in structural life, the FCL H1 was analyzed using the Crack 2000 software (Mello Jr. 1998). For the purpose of comparison, the model used was the same as Wieland (1995). The geometry and the other parameters for the analysis are described in the Crack 2000 output file, which is displayed below. CRACK GROWTH DATA Crack 2000 V. 3.0 (1998) - (c) 1995 Alberto W S Mello, Jr. All rights reserved. Run date = 11-11-2008 Run Time = 15:42:29 Cycle-by-Cycle Analysis AISI-SAE 4330V MOD, 180-200 UTS (Plt / Forg) Ys = 186 Uts = 190 Kc = 165. Kic = 112 Kie = 150 Superposition: Rten = 1 Rben-W = 0 Rben-t = 0 Rpin = 0 Crack Growth Model: Forman et al (1990) Corner Crack at Edge of Plate Geometry: W = 2.54 t = 2.13 Two-dimensional - Varying Crack Shape No retardation Model Figure 17 shows the crack growth curve for the original and the new DTA. It can be seen that the time for a crack to grow from 0.05 in to 0.85 in was reduced in more than 30%. This denotes a change in the inspection interval that will be proposed to the Maintenance Depot.

The implementation of the F-5M DTA Program allows FAB to recognize how the squadrons operate the aircrafts and how modernization can impact its structural life. The results will also help FAB to better use its resources, such as aircraft, spare parts, ground equipment and personnel. The old fighter was upgraded and now the new vector is heavier, but is also capable of performing a wider variety of missions. The only way to guarantee the flight safety is to know how the structure will behave in this new scenario. The tasks of a comprehensive DTA are evolving and are complex. With the available flight data, the assessment of stress spectra for fuselage, wing and horizontal tail FCLs was performed. The preliminary results show that some FCLs can have a major change in stress levels, which lead to different crack growth curves and different inspection intervals. Therefore, it is clear that the evaluation of DTA will contribute directly to the maintenance procedures at the F-5 Depot. The F-5M DTA Program will enable the Brazilian Air Force to accomplish its missions with the certainty that the structural safety is assured.

REFERENCES AFWAL-TR-82-3073, 1984, “USAF Damage Tolerant Design Handbook: Guidelines for the Analysis and Design of Damage Tolerant Aircraft Structures”. Wright-Patterson AFB Ohio, Final Report. Burnside, H., 1993, “Flying Longer: With Confidence”, Technology Today. Mattos, D.F.V., 2008, “Análise de Dados de Vôo das Aeronaves F-5M Para Cálculo de Vida em Fadiga”, pp.1874, Graduation Work, ITA, São José dos Campos. Mello Jr., A.W.S., 1998, “Crack 2000 Program: Software for Practical Fracture Mechanics and Damage Tolerance Analysis”, User's Manual, IAE, São José dos Campos. Mello Jr., A.W.S. et al., 2008, “Edição e Pré-Análise de Dados Operacionais do Projeto DTA F-5M: Software EPAD F-5M”, IAE, São José dos Campos (RENG ASA-I 03/08). Mello Jr., A.W.S. et al., 2009, “Geração de Ciclo de Tensões para Análise de Fadiga. Software GCTAF F-5M”, IAE, São José dos Campos (Submitted for approval). Northtrop Corporation, 1977, “F-5E/F Fatigue Loads for the Damage Tolerance Assessment”, Hawthorne, CA, (NOR 76-164)

Figure 17: FCL H1 crack growth. Journal of Aerospace Technology and Management

RIBEIRO, F. N., 2008, “Procedimentos a respeito da Coleta de Dados de Vôo das Aeronaves F-5EM e F-5FM utilizando o Programa F5DACOM”, IAE, São José dos Campos (RENG ASA-I 02/08). V. 1, n. 1, Jan. - Jun. 2009

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RIBEIRO, F. N., 2009, “Procedimentos para a Seleção de Dados de Fadiga das Aeronaves F-5EM e F-5FM utilizando o Programa SEDAF”, IAE, São José dos Campos (Submitted for approval). USAF, 1975,“Aircraft Structural Integrity Program: Airplane Requirements”. Wright-Patterson AFB Ohio, FSG-15GP, (MIL-STD-1530). USAF, 1974, “Airplane Damage Tolerance Requirements”. Wrigth-Patterson AFB. Ohio, (MIL-A-83444). USAF, 1975, “Airplane Strength and Rigidity Realibility Requirements, Repeated Loads and Fatigue”, WrigthPatterson AFB Ohio, O 45433, (MIL-STD-A-886B). Wieland, David H. et al., 1995, “ F-5 FMS Durability and Damage Tolerance Update Final DADTA Report F-5”, E. Southwest Research Institute, San Antonio, Texas.

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Thesis abstracts This section presents the abstract of most recent Master or PhD thesis related to aerospace technology and management

Characterization and quantification by FT-IR, HPLC and TG techniques of polymers used in plastic bonded explosive Elizabeth da Costa Mattos Institute of Aeronautics and Space beth@iae.cta.br

already appears to offer a base for the development of new methodologies applied in the aerospace sector.

Implementation of radial basis function networks on CMOS and BiCMOS technology Marcio Barbosa Lucks

Thesis submitted for PhD degree in Physics and Chemistry in Aerospace Materials at the Technological Institute of Aeronautics, ITA, São José dos Campos, São Paulo State, Brazil, 2008. Advisor: Dr. Rita de Cássia L. Dutra Key words: Plastic bonded, Polymer, Characterization, FT-IR, TG, HPLC. Abstract: High explosives are a tool that can be used in many areas of research and are critical components in both conventional and nuclear weapons. The desire to pack more energy into smaller volumes led to the development of Plastic Bonded Explosives (PBX). PBXs were developed to reduce the sensitivity of explosives, and are widely used in both civil and military applications when high performance is required. One method for obtaining an explosive charge is by pressing the explosive coating by means of a hydraulic press, and this represents the most important process in manufacturing high performance explosive charges. Since the weapons may be used in aggressive thermal and mechanical environments, it is important to characterize the PBXs, in order to know their behavior and properties. Therefore, contributing to the research on PBXs, a methodology was developed in this Thesis to characterize and to quantify the polymer content in PBXs by Fourier Transform Infrared Spectroscopy (FT-IR), using High Performance Liquid Chromatography (HPLC) and Thermogravimetry (TG) as reference techniques for the quantitative method. The proposed methodology for the quantification of polymers in PBXs, using the FT-IR technique of ATR and UATR reflection presented excellent results, being faster than the usual methodologies and eliminating the disadvantage of chemical residue generation. The development of the FT-IR methodology, including surface analysis techniques to quantify polymers constitutes a new line of research in our Research Center, Journal of Aerospace Technology and Management

Institute of Aeronautics and Space

lucks@iae.cta.br Thesis submitted for PhD in Electronic Engineering at the School of Engineering - UNESP Ilha Solteira, São Paulo State, Brazil, 2009. Advisor: Prof. Dr. Nobuo Oki Key words: Neural networks, Radial basis function networks, Integrated circuits, CMOS, BiCMOS. Abstract: In this work, we present the development of radial basis function circuits in CMOS technology. Two one-dimensional circuits, namely RBF1 and RBF2, are proposed for radial basis function realization, and their functionality is demonstrated by SPICE simulations and by their implementation with commercial MOSFET array integrated circuits. Multidimensional capability is demonstrated by the implementation of a bi-dimensional RBF1 circuit and by SPICE simulation results. In addition, BiCMOS versions are also presented for RBF1 and RBF2. The proposed cells are used in the design of bi-dimensional radial basis function neural networks in AMS 0.35µm CMOS process. In order to test their functionality, the networks were simulated for some applications with good results achieved. The issue of parameter quantization and its influence on the network function approximation capability is also dealt with in this dissertation. We carried out several simulations with different levels of quantization. The results obtained show that the network is capable of learning functions, even with a severe parameter quantization. As expected, the error increases for less bits of quantization. Nevertheless, the parameter quantization decreases the memory size and complexity necessary for network parameter storage, allowing the implementation of compact circuits and being adequate for low power applications. V. 1, n. 1, Jan. - Jun. 2009

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Thesis abstracts

Characterization of thermostructural materials based on carbon reinforced with carbon fibers (CRFC) and carbons modified with silicon carbide (SiC) Adriano Gonçalves Institute of Aeronautics and Space adriano@iae.cta.br Thesis submitted for PhD Degree in Aeronautics and Mechanics at the Technological Institute of Aeronautics, ITA, São José dos Campos, São Paulo State, Brazil, 2008. Advisors: Prof. Dr. Koshun Iha and Prof. Dr. Luiz Claudio Pardini Key words: Composite materials, Thermostructural composites, Characterization. Abstract In aerospace programs some materials are subjected to high temperatures and an aggressive thermal environment. To achieve these requirements there are a considerable number of resources that involve the development of composite materials based on Carbon Reinforced with Carbon Fiber (CRF) and Modified Carbon, especially with Silicon Carbide (SiC). To obtain materials that resist the thermal demands of a space vehicle, such as a protective structure for atmospheric reentry, or a rocket motor nozzle, or a component that acts as a thermal protection, is of strategic importance to the success of a space program success, such as the Brazilian program now under development. In the present work, some aspects of the usual process to obtain these materials, is examined, emphasizing the possibilities of carbon incorporation in the structure by chemical gas deposition or by liquid impregnation with pitch or phenolic resin. A study of the process variables in the national production of thermostructural composites, coming from three direction (3D) and four direction (4D) preforms, made by spatial arrangement of carbon rods, was undertaken. Thermal and microscopic characterization of the national composites was carried out, in addition to the characterization of four foreign composites originating from traditional producer countries.

Fluid-structure coupling on unstable vortex shedding phenomena in confined chamber Renato Felix Nunes Institute of Aeronautics and Space nunes@iae.cta.br Thesis submitted for PhD at University of Poitiers, French, Journal of Aerospace Technology and Management

2007. Advisor: Professor Son Doan-Kim and Frédéric Plourde Key words: Fluid mechanics, Iinstability, Vortex shedding mechanism, Fluid/structure coupling . Abstract: Analysis of a segmented flow field in a confined chamber was carried out in order to estimate the role of the vortex shedding sources. Specific attention was given to the potential interaction between vortex shedding that arises from the thermal inhibitor and vortex generation issuing from the injecting walls. Experimental investigations were carried out with an adapted cold gas experimental set-up and specific analyses studied the fluid/structure potential role of the two vortex sources of instability. Two different fluid/structure analyses were considered. First, a forced flapping movement induced by an adapted mechanical system made it possible to force the thermal inhibitor motion. A flexible obstacle was also analyzed in order to ascertain the potential passive control of instability. With a forced coupling, it was found that the wall injection vortex shedding dominated as source of instability while introducing a flexible obstacle provided a significant reduction in instability. The degree of this reduction was found to be linked to the thickness of the obstacle and the considered Mach number of the flow field. It strongly depended also on the internal geometry i.e. that directly controls the interaction of the vortex sources.

Evaluation and modeling of porosity type defects in solid propellant grains Silvio R. Macera Institute of Aeronautics and Space macera@iae.cta.br Thesis submitted for Masters in Engineering at Technological Institute of Aeronautics, ITA, São José dos Campos, São Paulo State, Brazil, 2008 Advisor: Dr. Lindolfo Araújo Moreira Filho Key words: Solid propellant, Rocket motor, Porosity. Abstract: This work presents a study carried out on bubble form imperfections and their influence on the burning evolution of the propellant grain. It discusses some of the main types of defects that can be found and the inspections and tests that can be carried out to detect and measure them. It also describes some types and forms that these defects may have and, based on their geometrical characteristics, a classification is proposed for further analysis and modeling of their burning evolution. Finally, this study covers a tension analysis evaluation for the S-30 motor propellant grain with and without the existence of defects. This study can be applied generally to other motors. V. 1, n. 1, Jan. - Jun. 2009

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Thesis Abstracts

Ablative carbon-phenolic composites additivated with carbon nanoparticles Marcus Luiz Pontarolli Technological Institute of Aeronautic pflow@uol.com.br Thesis submitted for Masters in Physics and Chemistry of Aerospace Materials at the Technological Institute of Aeronautics, ITA, São José dos Campos, São Paulo State, Brazil, 2006. Advisor: Professor Dr. Koshun Iha

method for use during rocket development projects in the Brazilian Air Force Institute of Aeronautics and Space Anderson de Oliveira e Silva Junior Technological Institute of Aeronautics andersonjr@ita.br Thesis submitted for Masters in Engineering at Technological Institute of Aeronautics, ITA, São José dos Campos, São Paulo State, Brazil, 2008 Advisor: Prof. Dr. José Henrique de Souza Damiani

Key words: Carbon-phenolic composites, Carbon nanoparticles, Ablation. Abstract: The development of solid rocket motor propellant began in Brazil, in the 70s. A solid propellant rocket motor is exposed to high temperatures, high pressures, high erosion rates, big thermal shocks without any conventional cooling system. Under these critical operating conditions, ablative polymeric composites and rubber liners are used for thermal protection of the motors' steel shell. Phenolic composites are normally used as ablative materials. Cotton, asbestos, carbon and silica woven cloths have been used in the last three decades as reinforcement for these composites. Lately, carbon woven cloth usage has received special preference. The main goal of this work was to produce and characterize pre-pregs and carbon-phenolic composites additivated with carbon nanoparticles. The literature shows that similar materials are used in high performance solid propellant rocket motors, such as in the solid rocket motor nozzle of the Space Shuttle. Three grades of carbon particles were used as additive in the phenolic matrix: micronized natural graphite, acetylene grade carbon black and furnace grade carbon black. Pre-pregs, were produced using a pilot impregnation equipment and three different additive concentrations 5, 10 and 15 per cent w/o were used. Prepregs without additive were also obtained. Eighty one specimens of carbon-phenolic composite were compression molded, nine for each carbon particle grade, plus nine for the phenolic composite without additive. Xray diffraction and Raman spectra were obtained both for the additives and for the reinforcement. The concentrations of the matrix, reinforcement and additives in the pre-pregs produced were measured together with flow and volatiles content. In the composite, the density, void content, heat transmission coefficient, linear thermal expansion coefficient, Iosipescu shear resistance, and oxyacetylene and plasma ablation resistance were evaluated. The results showed that composites additivated with carbon nanoparticles have better ablative performance than unfilled material. Moreover, the limits for each additive in the impregnation process were obtained.

Proposal of a risk management Journal of Aerospace Technology and Management

Key words: Risk, Risk management, Space vehicles development, project management. Abstract: This dissertation, proposes a method intended for managing risks during rocket development projects in the Brazilian Air Force Institute of Aeronautics and Space. After a bibliographical search and a study of best practices, several details were identified regarding risk management methods used in the main space agencies around the world and the specific characteristics of risk management applied to space vehicle development and to systems engineering. The proposed method intends to guide the activities of planning, the elaboration of a risk management plan, the activities of risk identification and analyses, the elaboration of risk response plans and other activities to do with tracking and control of project risks. To gauge the effectiveness of the proposed method, it was tested in a case study, related to development of the VS-15 rocket. As a result, the method was considered applicable, given that it makes it possible to keep a record, in an ordered manner, of several characteristic risks and to remove the adverse effects of unknown risks during the project life. The proposed method was considered feasible, even though it proved to require highly detailed and discriminating planning, especially in relation to human resources dedicated to risk management, the physical space necessary to archive the paperwork, the established timeline for these activities and the inherent costs. The proposed method was considered acceptable, within the limits of this work.

Application of the ammonium perchlorate particle packing study, and the use of a model for optimizing high performance composite propellant formulations based on HTPB and aluminum Maria Cecília C. Silva Institute of Aeronautics and Space mcecilia@iae.cta.br V. 1, n. 1, Jan. - Jun. 2009

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Thesis submitted for Masters in Physics and Chemistry of Aerospace Materials at the Technological Institute of Aeronautics, ITA, São José dos Campos, São Paulo State, Brazil, 2008 Advisor: Professor Koshun Iha Key words: Particle packing theories, Propellant, granulometry, Dibutyl thin laurate-DBTDL. Abstract: The aim of this work was to obtain formulations of AP/PBLH/Al-based propellant, in which the solid content was higher than that currently in use. The increase in the solid fraction enhances the rocket-motor thrust. However, it needs to adhere to a set of criteria, which were also subject of this work. These criteria are grounded in particle packing theories, which have been used as a tool for defining modality, distribution, granulometry and solid loading. Some trials were also performed to ascertain the applicability of a linear packing model. The model on trial proved to be applicable and the theoretical predictions agreed with experimental results. A further correlation model was proposed in this work to correlate the end-ofmix viscosity data at 50, 55 and 60oC under atmospheric pressure. Another correlation model was also proposed to correlate experimental data of Young modulus at 25oC. Both equations succeeded in correlating the experimental points. Ballistic properties were then determined for pressures ranging from 4 to 10 MPa. The effect of the order of addition of the bonding agent and aluminum were also evaluated. The best results were obtained when aluminum and the bonding agent were added at the beginning of the mixing process. The cure catalyst was also changed for DBTDL in the following trials in order to speed up the cure process. The tests carried out with 5 ppm of DBTDL displayed the best results for end-of-mix viscosity and further propellant properties. The use of high packing particle systems in conjunction with 5 ppm of DBTDL as cure agent permitted solid loading up to 88 per cent, far higher than the 84 per cent used in VLS propellant. Moreover, mechanical and ballistic properties of these propellants are suitable for the ongoing projects at IAE.

Evaluation of the applicability of FT-IR and thermal analysis techniques to the characterization and elastomer quantification Natália Beck Sanches Aeronautics Logistic Center nbsanches@uol.com.br Thesis submitted for Masters in Physics and Chemistry in Aerospace Materials at the Technological Institute of Aeronautics, ITA, São José dos Campos, São Paulo State, Brazil, 2008. Journal of Aerospace Technology and Management

Advisor: Dr. Rita de Cássia L. Dutra Key words: Elastomers, Characterization, FT-IR, Thermal analysis.

Abstract: The control of the qualitative and quantitative aspects of elastomer characteristics is very important. Therefore, the development of simple methodologies that allow characterization of these compositions is attractive to researchers in different areas of industry. This study evaluated the applicability of IR transmission techniques, ATR-Universal (UATR), TG and dynamic mechanical analysis (DMA) in the characterization and quantification of elastomeric compositions. Mechanical properties are used to complement this study. Pyrolysis and infrared spectroscopy (PIR-G/FT-IR) are used to investigate gaseous products of rubbers. The results demonstrate that this method is suitable to identify the different elastomers and elastomer blends, including rubbers that present similar IR spectra of pyrolysed liquid products. NBR samples with known contents of acrilonitrile (AN) were prepared at IAE laboratories. They were used as reference samples to construct an analytical curve to determine the content of AN in NBR by new methods of transmission (pyrolysis) and UATR/FT-IR techniques. Analytical curves permit the determination of the contents of AN in NBR samples of similar composition. TG/IR coupled technique is evaluated in the qualitative and quantitative aspects for some types of rubbers. Similarities and differences are observed in relation to known methodologies.

Dependability requirements analysis process for space software Marcos Alécio dos Santos Romani Institute of Aeronautics and Space mromani@iae.cta.br Thesis submitted for Masters in Aerospace Engineering at the Technological Institute of Aeronautics, ITA, São José dos Campos, São Paulo State, Brazil, 2007. Advisor: Prof. Dr. Edgar Toshiro Yano Key words: Dependability, Software, Requirements. Abstract: Given that software is beginning to assume an increasing number of functionalities in space systems, it is fundamental that the specification requirement activity should play a decisive role in the efforts to obtain a satisfactory and safe project. In critical aerospace systems, where ambiguity, non-completeness, and lack of requirements can cause serious accidents resulting in economic, material and human losses, it is necessary to treat the subject carefully. One of the ways to assure quality in space projects concerning safety, reliability and other dependability factors is to use techniques and safety factors V. 1, n. 1, Jan. - Jun. 2009

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to identify non-functional requirements during the project start phases, such as the system specifications. It is believed that the definition of what are the most important quality requirements for aerospace applications at IAE, and the most appropriate dependability techniques to evaluate them will produce maturity and stability for both the requirements and the project during its conception phase. The objective of this work is to develop a process to identify dependability quality factors in the development of software for space applications during its requirement specification phase. This work consists of a presentation of the most adequate dependability attributes for space vehicle software at IAE, and of an investigation of what are the most adequate safety analysis techniques to evaluate them so as to produce the most complete, consistent, and reliable requirements.

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INSTRUCTIONS TO AUTHORS Scope and editorial policy The Journal of Aerospace Technology and Management is the official publication of Institute of Aeronautics and Space (IAE) of the General-Command of Aerospace Technology (CTA), São José dos Campos, São Paulo State, Brazil. The Journal is published twice a year (June and December) and is devoted to research and management on different aspects of aerospace technologies. The authors are solely responsible for the contents of their contribution. It is assumed that they have the necessary authority for publication. When submitting the contribution the author should classify it according to the area selected from the topics:        

Acoustics Aerodynamics Aerospace Systems Applied Computation Automation Chemistry Defense Electronics

• • • • • • •

Management Systems Materials Mechanical Engineering Meteorology Propulsion Structures Vibration

The submissions, except thesis and book reviews, will be peer reviewed by three Editorial board members and selected for publication according to the editorial policy of the journal. Copyrights on all material published belong to IAE. Permission must be requested prior to use. Mandatory requirements All papers must include: type of contribution (review article, original paper, short communication, case report, book reviews or theses), title, authors' names, electronic addresses and affiliations, abstract, key words (3 to 6 items that should be based on NASA THESAURUS V.2- Access Vocabulary), and indication of the author responsible for correspondence. Contents Editorial Any researcher may write the editorial on the invitation of the editor-in-chief. The article should not exceed two pages. Review articles They should cover subjects falling within the scope of the journal. These contributions should be presented in the same format as a full paper, except that they should not be divided into sections such as introduction, methods, results and discussion. However, they must include a 150 to 200-word abstract, key words, concluding remarks, acknowledgment and references. The article should not exceed 18 pages. Technical papers These articles should report the results of original research and need to include: a 150 to 200-word abstract, key words, introduction, methods, results and discussion, acknowledgment, references, tables and/or figures. The article should not exceed 12 pages. Communications They should include a 150 to 200-word abstract, key words, tables and/or figures acknowledgment and references. The communication should not exceed 8 pages. Thesis abstracts The journal welcomes Masters and PhD thesis abstracts for publication. Journal of Aerospace Technology and Management

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Preparation of Originals Manuscripts should be written in English or Portuguese and submitted electronically by e-mail to revista.iae@iae.cta.br or revista.iae@gmail.com. The copies should be typed in a Word file according to the template that may be requested by e-mail to revista.iae@iae.cta.br. References References should be cited in the text by giving the last name of the author(s) and the year of publication. Either use "Recent work (Smith and Farias, 1997) or " Recently Smith and Farias (1997). With four (4) or more names, use the form "Smith et al. (1997)". If two or more references would have the same identification, distinguish them by appending "a", "b", etc., to the year of publication. Acceptable references include journal articles, numbered papers, dissertations, thesis, published conference proceedings, preprints from conferences, books, submitted articles, if the journal is identified, and private communications. References should be listed in alphabetical order, according to the last name of the first author, at the end of the article. Some sample references follow: Bordalo, S.N., Ferziger, J.H. and Kline, S.J.,1989, “The Development of Zonal Models for Turbulence”, Proceedings of the 10th Brazilian Congress of Mechanical Engineering, Vol.1, Rio de Janeiro, Brazil, pp. 41-44. Coimbra, A.L., 1978, “Lessons of Continuum Mechanics”, Ed. Edgard Blücher, S.Paulo, Brazil, 428 p. Clark, J.A.,1986, Private Communication, University of Michigan, Ann Harbor. Silva, L.H.M.,1988, “New Integral Formulation for Problems in Mechanics” (In Portuguese), Ph.D. Thesis, Federal University of Santa Catarina, Florianópolis, S.C., Brazil, 223 p. Soviero, P.A.O. and Lavagna, L.G.M.,1997, “A Numerical Model for Thin Airfoils in Unsteady Motion”, RBCMJ. of the Brazilian Soc. Mechanical Sciences, Vol.19, No. 3, pp. 332-340. Sparrow, E.M., 1980a, “Forced Convection Heat Transfer in a Duct Having Spanwise-Periodic Rectangular Protuberances”, Numerical Heat Transfer, Vol.3, pp. 149-167. Sparrow, E.M., 1980b, “Fluid-to-Fluid Conjugate Heat Transfer for a Vertical Pipe-Internal and External Natural Convection”, ASME Journal of Heat Transfer, Vol.102, pp. 402-407. Associação Brasileira de Normas Técnicas, 2002, NBR6032: “ Abreviação de títulos de periódicos e publicações seriadas”, Rio de Janeiro, Brazil 14p. BRASIL,1993, “Relatório de atividades”, Ministério da Justiça, Brasília,D.F. Brazil 28p. Garcia,A.,2005, “Estudo Preliminar de Concepção de Performance de Veículos Lançadores Referentes aos Estudos do Grupo de Trabalho VLS-2010”, IAE, São José dos Campos, Brazil. (ASE-RT-006-2005) EMBRAPA, 1995, “Unidade de Apoio,Pesquisa e Desenvolvimento de Instrumentação Agropecuária”. Medidor digital multissensor de temperatura para solos, BR n. PI 8903105-9, 26 Jun.1989,30 maio 1995. Illustrations All illustrations (line drawings, photographs and graphs) should be submitted, preferably in JPG, TIFF or XLS format, with good definition (1 to 2 Mega Pixels) References should be made in the text to each illustration. Explanations should be given in the figure legends, so that illustrations are kept clean. Tables Authors should take notice of the limitations set by the size and layout of the journal. Therefore, large tables should be avoided. All tables must be mentioned in the text. Sponsors This publication is sponsored by Institute of Aeronautics and Space (IAE) Journal of Aerospace Technology and Management

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