IM 3 2018 EN by Innovatieve Materialen

Volume 3 2018

Efficient use of resources in manufacture of metal components The Glass Spaceframe 3D printing large scale metal objects TERRA-ink: 3D printing with local soil Carbon Nanotube Array

I N T E R N A T I O N A L

E D I T I O N

CONTENT Innovatieve Materialen Aboutis een vaktijdschrift gericht op de civieltechnische Innovatieve Materialen sector en bouw. Het bericht over ontwik(Innovative Materials) is a digital, kelingen op het gebied van duurzame, inindependent magazine novatieve materialen en/of de about toepassing material the fields of daarvaninnovation in bijzondereinconstructies.

engineering, construction (buildings, infrastructure and industrial) and Innovatieveindustrial Materialendesign. is een uitgave van Civiele Techniek, onafhankelijk vaktijdschrift voor civieltechnisch ingenieurs werkzaam in de grond-, weg- en waterInnovatieve Materialen has bouw en verkeerstechniek.

entered partnerships with several intermediate and De redactie staatorganisations open voor bijdragen universities, allUactive in the field of van vakgenoten. kunt daartoe contact materialmet innovation. opnemen de redactie. More information (in Dutch): www.innovatievematerialen.nl A digitalUitgeverij subscribtion in 2018 (6 editions) costs € 39,50 (excl. VAT) SJPofUitgevers Members KIVI-leden and students: Postbus € 25,(excl.861 VAT) 4200 AW Gorinchem tel. (0183) 66 08 08 Publisher e-mail: info@innovatievematerialen.nl SJP Uitgevers www.innovatievematerialen.nl

Postbus 861 4200 AW Gorinchem Redactie: tel. +31 183 66 08 08 info@innovatievematerialen.nl Bureau Schoonebeek vof Hoofdredactie: Gerard van Nifterik

Editor

Gerard van Nifterik

Advertenties Advertizing & Drs.sponsoring Petra Schoonebeek

Drs. Petra Schoonebeek

e-mail: ps@innovatievematerialen.nl

Innovative Materials

Een digitaal abonnement in 2016 (6 uitgaven)platform: kost € 25,00 (excl. BTW)

Dr. ir. Fred Veer, prof. Ir. Rob Nijsse (Glass & Transparency Research Zie ook: www.innovatievematerialen.nl Group, TU Delft), dr. Bert van Haastrecht (M2I), Niets uitWim deze Poelman, uitgave magdr.worden prof. Ton verveelvuldigd of openbaar worden Hurkmans en (MaterialDesign), door middel van herdruk, fotokopie, miprof.dr.ir. Jos Brouwers, crofilm of op welke wijze dan ook, zonder (Department of the Built voorafgaande schriftelijke toestemming Environment, Section van de uitgever.Building Physics and Services TU Eindhoven), prof.dr.ir. Jilt Sietsma, (4TU.HTM/ Mechanical, Maritime and Materials Engineering (3mE)

NEWS 8 Efficient use of resources in manufacture of metal components

In the newly opened 3D-Printing Lab for Metals and Structural Materials at the Fraunhofer Institute for High-Speed Dynamics, Ernst-Mach-Institut, EMI, researchers have investigated how resource- efficient the manufacturing process is when lightweight aluminium components are manufactured using additive methods. They discovered that even marginal reductions in the material and resources used per component yield high cost savings in series manufacturing.

12 The Glass Spaceframe

The ‘Glass and Transparency Research Group’ of Delft University of Technology focusses on research and education in the field of structural glass. One of the courses in which the group is involved, is the glass part of the minor ‘Bend and Break’. In 2016, students worked on the development and manufacture of glass parts for the ‘Glass Truss Bridge’ which was actually built last year on the TU Delft campus

16 3D printing large scale metal objects

3D printing (Additive Manufacturing) of large metal objects is still in its infancy. Nevertheless Additive Manufacturing of large metal components has many advantages, especially in terms of design, production speed and costs. However, in order to be able to produce large metal products, new knowledge is needed and this still needs to be built up. A Dutch partnership between industry, two universities and knowledge intermediary M2i, recently achieved a breakthrough with the 3D printing of a 400-kilo heavy-duty screw propeller. According to the parties involved, that is just the beginning.

20 TERRA-ink: 3D printing with local soil

24 Carbon Nanotube Array: Scaffolding Material for Opto-, Electro-, Thermo-, and Mechanical Systems

Nanomaterials, unlike bulk materials, can be grown bottom up in a controlled manner. The ability to accurately control their behaviour and properties are a great asset for applications requiring design for reliability. Carbon nanotubes (CNTs) have a set of particular optical, electrical, thermal, and mechanical properties and thus offer very attractive and promising possibilities for a range of applications. From an academic perspective, CNTs are praised to be the next scientific discovery that would revolutionise many industrial areas, especially those in which material strength is a key property. However, from a commercial perspective, the current state of the art is not sufficient for practical applications and therefore more research is needed. Here, we present a brief overview of our research activities regarding future applications of CNTs in opto-, electro-, thermo-, and mechanical microsystems.

Cover: The Glass Spaceframe, (detail) TUDelft (pag. 12)

INNOVATIVE MATERIALS 3 2018

NEWS

Tiles of recycled rubber Researchers from the Argentinean Centro Experimental de la Vivienda Económica (CEVE-CONICET) (Experimental Center for Economic Housing) have developed a method to make tiles with recycled rubber. The rubber comes from industrial waste and from discarded tires. Thanks to its composition, CEVE tiles are lighter and more flexible, resistant to hail and with a higher insulating insulation and watertightness than conventional tiles. The material was developed by CEVE in collaboration with the Instituto CINTEMAC of the Universidad Tecnológica Nacional, Facultad Regional Córdoba, Argentina. The collaboration led to a production process in which ground rubber from industrial waste and used tires are pressed using an extruder. According to the developers of the system, it’s a sustainable product for roofing, because it is made from the reused waste. Moreover, the rubber tiles would be more resistant to deformation, freezing and hail compared to traditional tiles, such as ceramic or concrete. In addition, they are lighter. The project is currently still in an expe-

rimental phase, with the aim of obtaining the corresponding certification for subsequent commercialization. www.ceve.org.ar (Spanish)>

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HĂŠt expertisecentrum voor materiaalkarakterisering. Integer, onafhankelijk, objectief onderzoek en advies. ISO 17025 geaccrediteerd. Wij helpen u graag verder met onderzoek en analyse van uw innovatieve materialen. Bel ons op 026 3845600 of mail info@tcki.nl www.tcki.nl

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09-05-17 13:19

Materials 2018 Trade fair and congress

Materials are at the base of everything we see around us. They are often taken for granted, but where would we be without our cars, machines, and buildings without a strong base? We almost forget how special materials are and how complex the selection, creation and production processes are. Not to mention about developments and innovations within these fields. On May 30 and 31 2018, the 6th edition of Materials will take place at the NH Conference Centre Koningshof in Veldhoven, the Netherlands. During these two days, Materials will be the largest meeting point for material specialists, product developers and engineers. An all-in-concept will be presented, based on the 4 elements for finding a solution for material challenges:

Visit www.materials.nl>

Materials 2018, trade fair & congres: 30 en 31 mei 2018, Veldhoven, The Netherlands

CLICK HERE FOR YOUR FREE TICKET!

NEWS

Full span of the 3D printed bridge is finalized Last April, the full span of the MX3D bridge was finalized. MX3D is 3D printing a fully functional stainless steel bridge to cross one of the oldest and most famous canals in the center of Amsterdam, the Oudezijds Achterburgwal. MX3D equipped typical industrial robots with purpose-built tools and develop the software to control them. The unique approach allows us to 3D print strong, complex and graceful structures out of metal. The goal of the MX3D bridge project is to showcase the potential applications of the MX3D multi-axis 3D printing technology.

The Bridge is designed by Joris Laarman Lab, Arup is the lead structural engineer, ArcelorMittal provides the metallurgical expertise, Autodesk assists with their knowledge on digital production tools, Heijmans is the construction expert, Lenovo supports the project with computational hardware, ABB is the robotics specialist, Air Liquide & Oerlikon know everything about welding and lastly, Plymovent protects the air in the production area whilst AMS and TU Delft do invaluable research. Gemeente Amsterdam is the first customer of the bridge building department.

The bridge will be presented in October of this year. It will actually be placed according to schedule in 2019. http://mx3d.com>

Video

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NEWS

Cast Basalt tiles During the Material Xperience, organized earlier this year by Materia, tegels.com presented various products made of cast basalt, produced by Eutit. This Czech company produces two basic materials: melted basalt and a material with trade name Eucor, also based on basalt. Melted basalt is processed from raw material, which is, according to Eutit, unique by its material composition. From melted basalt, which features excellent properties, particularly abrasion and chemical resistance, the company produces huge amount of products of wide applicability. Eucor features the same properties, and additionally it is resistant to high temperatures, and is used exclusively in industrial operations as abrasion-resistant insert protecting the piping.

Basalt

Basalt is natural material-stone, which belongs to such materials, whose lifetime has exceeded not only centuries, but also millenniums. But its hardness and difficult processability limited its wider expansion in constructional sector. As late as

4 | INNOVATIVE MATERIALS 3 2018

in 20th century the stone features much wider application in industry and civil engineering with development of petrurgy, i.e. processing of non-metallic ores by melting and casting. Basalt is continuously melted in pit-type furnace heated by natural gas at approx. temperature 1280Â°C. At 1200Â°C it is cast (shaped) into metal or sand moulds, and after removing it is stored into continuous cooling tunnel furnaces till cooling after 16 - 21 hours, where it re-crystallizes and gains its end-use properties.

NEWS Eutit produces various products from the melted basalt and this amount is ever increasing. Main groups of products from melted basalt are pavements, tubes, sewerage gutters, tubes, bricks and more. Eucor is a material produced by melting of suitable raw materials in electric arc furnace at temperature exceeding 2000 Â°C followed by crystallizing of resulting melt. The melt is cast into sand moulds by common casting method. According to Eutit, Eucor features excellent properties, particularly hardness, resistance against high temperatures and chemical corrosion. Due to its hardness they are applied under conditions of extreme heavy abrasive load, such as pneumatic transport of silica sand, sinter, mainly in the piping bends. Other examples cover lining of separators, spiral chutes, dragline conveyors, concrete mixers, blenders etc. Resistance against high temperatures enables use for masonry of glass furnaces above the melt level, special shape pieces of burner walls and burners themselves, shape pieces of regenerative chambers, coke-oven platforms etc. An interesting opportunity is use in fly-ash separators with high entry temperature, where all stated properties, incl. chemical resistance, might be used. Due to its high strength and abrasive resistance the Eucor may be successfully applied in certain metallurgic operations for transport of scale and slag. More on www.eutit.com> www.tegels.com>

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Structurally optimized wheel bearing for an ultralightweight vehicle designed for Additive Manufacturing â&#x20AC;&#x201C; made in the 3D-Printing Lab for Metals and Structural Materials at Fraunhofer EMI (Photo: Fraunhofer EMI)

Efficient use of resources in manufacture of metal components In the newly opened 3D-Printing Lab for Metals and Structural Materials at the Fraunhofer Institute for High-Speed Dynamics, Ernst-Mach-Institut, EMI, researchers have investigated how resource- efficient the manufacturing process is when lightweight aluminium components are manufactured using additive methods. They discovered that even marginal reductions in the material and resources used per component yield high cost savings in series manufacturing. The 3D-Printing Lab for Metals and Structural Materials at Fraunhofer EMI in Freiburg houses one of the largest commercially available 3D printers for metal currently in existence. Using the selective laser melting, metal structures with dimensions of up to 40

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centimeters can be made by additive manufacturing. 3D printing offers completely new ways of designing components with highly complex shapes and optimizing their weight. But it is only by combining Additive Manufacturing and intelligent lightweight design that

you can maximize resource efficiency in manufacturing. Fraunhofer researchers in the 3D-Printing Lab have investigated just how economical the manufacturing process is in terms of resources, and whether material and operating costs can be minimized compared to

Lattice cube with edge length of 40 centimeters, one of the largest metal structures manufactured using selective laser melting (SLM) (Photo: Fraunhofer EMI)

conventional industrial methods. To do this, they took a practical, widespread component for their tests: a wheel carrier such as might be used in a lightweight vehicle. The focus was on energy and material consumption, the manufacturing time and the CO2 emissions that arise during the smallscale production of twelve wheel bearings. After the researchers had used the numerical finite element method (FEM) to simulate and analyze a draft design and determine the right geometric shape with structural optimization methods, they constructed the wheel bearing in an optimized lightweight design. The result was a wheel bearing designed for the defined load scenarios and offering maximum performance. Because of their geometric complexity, structures produced in this way cannot be manufactured by conventional methods such as milling or turning. According to Klaus Hoschke, scientist and group leader at Fraunhofer EMI, with the lighter model, the team was

able to save hugely on resources during production, as less material has to be produced per component. If this is multiplied by the number of units in a small-scale run, it will require less time, material and energy for manufacturing.

Reducing volume through the use of higher-strength materials offers the greatest potential for energy savings here, Hoschke said. Using the numerically optimized version

Several structural components arranged on a base plate after a selective laser melting process (Photo: Fraunhofer EMI)

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Finite element analysis of the start design of a wheel bearing technology demonstrator (left); numerical design optimization of the technology demonstrator to reduce the component’s mass without impairing functionality (center); and CAD template for manufacturing the 3D metal component (right) (Photo: Fraunhofer EMI)

of the wheel bearing, 15 percent less energy was required for the additive process than for the conventional method. Manufacturing time was cut by 14 percent and CO2 emissions by 19 percent. And where material consumption was concerned, it could be significantly reduced by 28 percent. Forecasts on what effect the Additive Manufacturing of metals will have on

global production vary widely. But everyone agrees on one thing: for many industries – such as aerospace, automotive engineering, medical engineering and toolmaking it is a game changer, Hoschke thinks. In the future, he and his team want to research the extent to which other design heights, series sizes and materials such as titanium affect the resource efficiency of the manufacturing process.

Text: Fraunhofer>

Selective Laser Melting (SLM) Selective Laser Melting (SLM) is an Additive Manufacturing technique that involves building up objects layer by layer. The starting point for the manufacture of metal components via SLM is the use of metal powder, which is applied to the construction platform – much like the icing on a cake – and melted in defined areas by laser radiation. The metal powder solidifies and a new layer of powder is applied with defined layer strength. In this way, a homogeneous 3D component with complex geometry is built up. The big advantage of the method is that structural material is generated only in those places where it is actually needed. Moreover, you can reuse the unmelted metal powder. This ensures that manufacturing processes are economical in their use of material.

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Materials 2018 On May 30th and 31st Mikrocentrum organizes the sixth edition of Materials, trade fair and congress, in Veldhoven: an inspiration meeting with everything about materials, analysis, surface & connection techniques. A meeting that has to inspires and where solutions can be found. www.materials.nl>

Visit Materials 2018 Click here for your free ticket! 9 | INNOVATIVE MATERIALS 3 2018

The Glass Spaceframe Figure 1 - The glass trusses built by the students of Bend and Break of TU Delft

Figure 2 - The Glass half-timbered bridge on the campus of TU Delft

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Figure 3 - Assembly of the bars and connection to Mero balls

Figure 4 - Close up of the connection

Initially, the design of the rods of the bridge was based on the principle of the glued bundle, previously developed by the group (Oikonomopoulou, van den Broek, Bristogianni, Veer, & Nijsse, 2017). This time the challenge was nothing less than constructing a glass spatial truss, entirely without glue. This is possible by pre-tensioning the strutt and embedding the glass rods in the end plates (see Figure 3). To make the connection

between the bundle and the node (a classic spaceframe node made by Mero), special adaptor tubes were made by technican Kees Baardolf. These adaptor tubes can be scewed on the pre-stressed rod on one side. On the other side they are equipped with the Mero fixing system (see Figure 4).

Figure 5 and 6 - Testing the glass bars on pressure in the Stevin-II lab

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Figure 7 - Pre-stretching the glass bars

Within two weeks, the students cut the glass rods to length and post-processed them in the lab afterwards. They assembled the rods and pretensioned them so that the first rods could be tested for

Figure 9 and 10 Assembling the final framework

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Figure 8 - Close up of the button

compression and buckling (see Figures 5 and 6). These compression tests are important for determining the critical load, so the students could not only obtain values for calculations of their

own designs, but also could observe if the force from the head plate is properly introduced into the glass, via the rubber rings that are intended for this purpose. Thereafter the rest of the rods were

assembled and pretensioned (see Figure 7). With these pre-stressed bars, the students have built the space frame (Figure 9). This space frame is meant as a demonstration to get a â&#x20AC;&#x2DC;feelingâ&#x20AC;&#x2122; with this type of construction. After all, they had to design, detail and calculate a project of their own with the principle of glass spacetruss construction. Authors: Ate Snijder and Christian Louter Oikonomopoulou, F., van den Broek, E.A. M., Bristogianni, T., Veer, F.A., & Nijsse, R. (2017). Design and experimental testing of the bundled glass column. Glass Structures & Engineering, 2 (2), 183-200. doi: 10.1007 / s40940-017-0041-x Figure 11 - Air bridge (student design)

Figure 12 - Visitors center The Green Village (students design)

Visit Materials 2018 On May 30th and 31st Mikrocentrum organizes the sixth edition of Materials, trade fair and congress, in Veldhoven: an inspiration meeting with everything about materials, analysis, surface & connection techniques. A meeting that has to inspires and where solutions can be found.

Click here for your free ticket!

www.materials.nl>

13 | INNOVATIVE MATERIALS 3 2018

3D printing large scale metal objects 3D printing (Additive Manufacturing) of large metal objects is still in its infancy. Nevertheless Additive Manufacturing of large metal components has many advantages, especially in terms of design, production speed and costs. However, in order to be able to produce large metal products, new knowledge is needed and this still needs to be built up. A Dutch partnership between industry, two universities and knowledge intermediary M2i, recently achieved a breakthrough with the 3D-pronating of a 400-kilo heavy-duty screw propeller. According to the parties involved, that is just the beginning.

Additive Manufacturing (AM) of large metallic components relies on prediction and control of key material properties, requiring the development of new, powerful models and a significant advance in know-how. Several processes exist to build 3D metallic components and the choice influences the build rate (measured in mass per unit time), as well as the feature size and build quality of the final

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product. To date, technological developments have focused primarily on processing and property issues, aimed at high accuracy, small-scale constructs using powder-bed technologies, with feature sizes typically of the order 10-4 m. Large-scale AM processes do not suffer from many of the manufacturing constraints that are commonly associated

with the small-scale, such as the requirement for additional support structures or limitation to a single (horizontal) build plane. However, they often give rise to a significant degree of microstructural anisotropy, which in turn leads to orientation dependence in the mechanical properties. In addition, the degree of residual stresses that develop within a component

due to processing conditions can lead to unacceptable part deformation or even catastrophic failure due to cracking, a risk that is exacerbated by the anisotropic nature of the microstructure. The development of direct metal deposition technology for large scales has received comparatively little attention, despite the potentially huge impact for engineering applications.

Advantages include the ability to construct parts where and when needed; the novel capability to design components with radically different properties within one compact monolithic component (e.g. strength, wear or corrosion resistance, mass, electrical property variations etc.); high-speed manufacturing of unique or small series products and the potential to join (metallurgically)

Video: the making of

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incompatible materials through the deposition of graded intermediate layers.

Potential

3D printing of metal components is a technology that will potentially revolutionize manufacturing industry in the next years. Therefore, EU at an international level as well as several countries at a national level, including The Netherlands, are promoting specific funding programs to strengthen the research in this area and stimulate aggregations between academic and research organizations working in this field together with industries interested in the exploitation of the results. According to the Dutch National Research Agenda, 3D printing is a game changing technology with enormous potential impact on the range of available designs, enabling new component capabilities that cannot be realised with any other technology, facilitating onsite/ remote fabrication and reducing leadtimes, storage and transportation costs. Successful construction of large-scale

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(1 to >10 m) additively manufactured metallic components for safety-critical applications requires a thorough understanding of metallurgical structures, residual stresses and associated mechanical properties. These in turn are critically influenced by factors governing the composition and thermal-mechanical history of each 3D volume element within a component, including thermal input, cooling rates, stress evolution, build orientation, component design and heat treatments.

The first breakthrough

The â&#x20AC;&#x2DC;Rotterdam Additive Manufacturing LABâ&#x20AC;&#x2122; (RAMLAB) is the first 3D printing field lab that focuses on the maritime industry. Using 3D metal printer replacement ship components can be manufactured within a few days, instead of traditional several months period. RAMLAB was initiated by the Port of Rotterdam Authority, InnovationQuarter and RDM Makerspace. A year ago, they have established a close collaboration with Materials Innovation institute

(M2i), known to be a connecting link between industry and knowledge institutions. As a network organization, M2i carries out material research together with about 100 industrial and academic partners. The first 3D printed ship propeller, WAAMpeller, is a product that the Ramlab, together with its partners on the one hand and the technical universities Delft and Twente on the other hand worked together, is one of the examples where M2i has played a leading role in the linking the right knowledge carriers to specific industrial needs. WAAMpeller is made with Wire Arc Additive Manufacturing, the 3D printing process with welding wire. With a weight of 400 kilos, a breakthrough has been achieved in the 3D printing of large-scale metal products. The result that has been achieved forms the basis for producing even larger and more complex product designs in the future. Two M2i researchers, Wei Ya (UT) and Constantinos Goulas (TU Delft) were among the ones who made this breakthrough possible.

Print from products to properties

‘We are very proud of the first steps that have been taken in 3D printing of large-scale metal products, but we are going further,’ says Bert van Haastrecht, General Manager of M2i. ‘Much more knowledge needs to be developed until the technology is adapted by the industry. From optimizing material properties and automating the printing process to big data analyzes for machine learning and product topology optimization. We will continue these steps in a recently approved by NWO-TTW Perspective program AiM2XL. Within this program, under the leadership of Prof. dr. Ian Richardson of TU Delft, together with a consortium of 24 partners, we will study the properties of the printed material to the micro level and make models that can predict and control the behavior of the entire object. Additionally, we would like to transform some of the disadvantages/limitations of the method (multiple thermal cycles, internal stresses, etc) into useful degrees of freedom to build graded materials with the right microstructure and internal stress at the right place.’ ‘The program paves the way for a new, material-oriented approach in which suitable model combinations will be used to design and manufacture on-demand material properties at specific locations within a structure. Successfully implemention of the program will put the Netherlands in a leading position in the production of large metal components.’

M2i Materials innovation institute (M2i) is a network organization specialized in materials research. Our core mission is to support both the industry and society in finding solutions for materials-related questions in product development and production processes. M2i connects industry, academia and research institutes across The Netherlands and Europe. As a network organization, M2i has insight in materials-related activities in The Netherlands and Europe. M2i collects research questions from industrial partners and connects them to the research partners with the right expertise. M2i helps its partners in defining open innovation research programmes. A significant portion of the projects are organized in cooperation with NWO and industry. More at M2i>

Text: Viktoria Savran Program Manager M2i

Two M2i researchers involved, Wei Ya (UT, left) and Constantinos Goulas (TU Delft)

3D printed ship propeller surface, unpolished, at the Materials Xperience, March 2018

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3D printing with local soil

TERRA-ink

In recent years, natural disaster and military conflicts forced vast numbers of people to flee their home countries, contributing to the migration crisis we are facing today. According to the UNHCR, the number of forcibly displaced people worldwide reached the highest level since World War II. Post-disaster housing is by nature diverse and dynamic, having to satisfy unique socio-cultural and economical requirements. Currently, however, housing emergencies are tackled inefficiently. Focusing on temporary shelters suitable for the transitioning period between emergency accommodation and permanent housing, TERRAink addresses new construction methods that allow for time and cost efficiency, but also for flexibility to adapt to different contexts. The concept was presented at Gevel 2018 (January) and Materal Experience (March). TERRA-ink aims to develop a method for layering local soil, by implementing 3D printing technologies. The use of locally sourced materials in combination with additive manufacturing is investigated aiming at reductions in financial investments, resources and human labour, as well as at simplified logistics, low environmental impact and adaptability to different situations and requirements. Such a building system has the potential

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of combining low- and high-tech technologies, in order to facilitate a fully open and universal solution for large scale 3D-printing using any type of soil.

Mixture

During the project, the use of both local materials and generic machineries were investigated. Soil material was studied focusing on the material

properties of various mixtures in dry and wet conditions. Different mixtures (clay + aggregates) were considered, in order to define how various clay types and grain size affect the physical and mechanical properties of the material. Then, compression tests were conducted on dried soil samples. The results were used to define the compressive strength and other parameters for the structural analysis. The influence of additives and

different kind of natural fibres (straw, jute and hay) was confirmed to be an important aspect in the design of the mixture, as the fibres in the mix increase the tension resistance of the soil and reduce the shrinkage.

Extrusion

the material. By studying the interaction of the machines with the liquid soil mixture and its deposition, it was possible to define and highlight the main parameters that influence the correct design of a soil mix. Additionally, investigations were made on the design options, regarding the

geometric configurations and structural behaviour of the shelters. As a test case, a simple shelter design was analysed to identify solutions using as little material as possible (simultaneously reducing the printing-time), but still achieving good structural stability.

Besides studying the mechanical performance of dried soil, the project investigated the properties of the mixture when in fluid state. Its behaviour was analysed during the extrusion process used to deposit the material in layers. Parallel to the material studies, the project focused also on the hardware developments, since it also affects the extrusion process. More specifically, commonly available machineries are utilized in this project, in order to explore an alternative open-source solution for large scale 3d-printing that can be applied in all emergence situations. This approach offers simplified logistics and reduced costs, especially when compared with existing technologies such as robots or big commercial printers. An industrial clay pug-mill and a concrete mixer were tested to define the characteristics that allow a good extrusion of

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Shape and geometry

Since curved shapes are generally faster to produce by 3D-printing, a simple round-shaped solution in plan was examined first. Compared to other geometries, round shapes offer also the additional benefits of being earthquake resistant due to their symmetry in all directions. After defining the boundary conditions (such as maximum dimensions of printing area and structural properties, based on laboratory tests and literature) structural optimization was used to identify the optimum geometries. Nevertheless, they indicated domes and cones as the most efficient shapes. Furthermore, irregularities in the wall surfaces (such as openings) were examined in order to identify the limitations in dimensions and the best geometries for doors and windows. Using 1:1 scale printed samples, on-going tests aim at determining which geometries can be actually produced. In fact, the shape and geometries of the shelter are also a consequence of the printing process. During the deposition, the liquid material tends to deform and eventually settle under its own weight. When occurring in rather uncontrolled environments the impact of this process can be high.

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The lack of stiffness and stability of the layer can be counteracted by its geometry. A flower shape layer deposition can drastically improve the stability of the

overall structure, until the mixture is dry enough to withstand its own weight. For this purpose, a second external layer is printed in order to give extra support

during the extrusion process and contribute to redistribute the stresses once the wall is dry. This external layer is also a useful protection against atmospheric conditions. The inner gap could provide benefits in terms of ventilation or can be filled with insulation material, depending on the local climate. During the process, several small-scale tests were made. A 1:1 scale prototype of a wall portion is being realized as a proof of concept. The prototype will be used also to further test the geometries and the structural performances

Potential

Though more research is necessary to develop the construction system, the current results show its potential of applicability, probably resulting in a significant improvement in the emergency relief field. Besides that, the further benefits of soil as a building material are highlighted. Over the past centuries, soil was always used; but nowadays it is often underestimated or associated to modest constructions. Today, in combination with innovative technologies, it could be reconsidered and regain its relevance. Delft University of Technology Tommaso Venturi, dr. Michela Turrin MSc Arch, Foteini Setaki Msc Arc, dr.ir. Fred Veer Eindhoven University of Technology ir. Arno Pronk, Prof.Dr.-Ing Patrick Teuffel, Yaron Moonen, Stefan Slangen, Rens Vorstermans https://www.4tu.nl/bouw/en/

21 | INNOVATIVE MATERIALS 3 2018

RESEARCH

Carbon Nanotube Array:

Scaffolding Material for Opto-, Electro-, Thermo-, and Mechanical Systems

Carbon nanotube array, wall and forest; Photo: KEYENCE

Carbon nanotubes (CNTs) have attracted great interest since their discovery in 1991; both from a fundamental scientific point of view and for future applications. Scientists have demonstrated extraordinary properties of CNTs, including thermal conductivity higher than diamond, mechanical strength higher than steel, electrical conductivity better than copper, and the possibility to absorb more light than super-black paint. Because of these extraordinary properties, researchers from the ‘Electronic Components,

22 | INNOVATIVE MATERIALS 3 2018

Technology and Materials (ECTM)’ group of Delft University of Technology (TU Delft) are investigating the use of CNTs as a building block and scaffold for enabling unique micro/nanostructures for opto-, electro-, thermo-, and mechanical applications. In this paper, several examples of significant breakthroughs that resulted from our group research on CNTs are highlighted.

Synthesis at low temperature

Catalyst nanoparticles typically require a high temperature to start the catalytic reaction for growing high density CNTs. This is undesirable when the CNTs have to be integrated on top of electronics or with polymers, as a high growth temperature can damage the existing devices. By optimizing the catalyst-support layer stack to reduce the activation energy, we achieved a record-low temperature (350 °C) wafer-scale deposition process of CNTs to make them compatible with

RESEARCH molding compound demonstrates that, next to the required thermal conductivity, the mechanical compliance for thermal interface applications can be achieved [5].

Application in optical systems

Figure 1. Holes filled with CNTs grown at different catalysts and temperatures: (a) Co, 350 °C; (b) Co, 400 °C; (c) Fe, 500 °C; and (d) Fe, 550 °C; Image adapted from [1].

CNTs are one of the blackest materials known and can absorb radiation over a broad wavelength range. Combined with optically transparent silicon rubber, this allows us to create Fresnel lenses of which the focal point can be changed by stretching [6]. The low cost and scalable manufacturability of this device provides solutions for disposable microscopes, which are valuable for health diagnostics. Figure 4 shows the fabricated device. Such flat optics find their way into miniaturized photonic chips, integrated optics, optical interconnects, beam focusing or mask-less lithography systems, but can also be used for deflecting and collimating tasks in optical sensor systems or for optical data transfers.

standard back-end-of-line semiconductor fabrication and to allow potential integration with modern dielectrics and some types of flexible substrates. Figure 1 shows images of CNTs grown in a hole with commonly used cobalt and iron catalysts at different temperatures [1]. The average diameter of a single CNT is about 10 nm with a density in the order of 5.1010 tubes/cm2.

Tailoring the mechanical properties

The porous nature of CNT arrays allows for the unique opportunity to tailor their mechanical response and functionality by the infiltration and deposition of nanoscale conformal coatings. CNT arrays with various thicknesses of SiC coating allow the tuning of the mechanical properties of CNT bundles over a wide range: starting from foam-like behavior to materials as hard as ceramics [2]. Simulation and experimental observations in Figure 2 have shown that a SiC coating can change the failure mode from collective buckling to fracture [3].

Investigating thermal performance

The performance of modern high-density and highly functional devices are often severely limited by overheating. Therefore, the thermal management may well be the major bottleneck of the next electronics revolution. Since carbon allotropes and their derivatives possess superior thermal properties, are inert and have low density, carbon-based nanostructured materials appear to be the most promising candidates for achieving lightweight and local heat dissipation. In order to make a step toward the implementation of high aspect ratio CNTs as effective thermal management solution it is necessary to quantify their as-grown thermal properties. A non-destructive in situ characterization method for hierarchical structured porous materials, which combines MEMS technology, electrical characterization and high-resolution thermographic analysis, was developed [4]. Moreover, the foam-like morphology of CNTs allows the infiltration of conformal coatings within the array, achieving a hybrid composite with enhanced thermal performances [5]. Last but not the least, the CNT scaffold concept opens the route toward the application of vertical CNTs as thermal interposer. In fact, the integration of coated high aspect ratio CNTs in an epoxy

Figure 2. Mechanical compression of CNT’s (a) Flat-punch nano-indentation on a vertically aligned a CNT pillar, (b) Smooth localized micro buckling on CNT pillar, (c) Fracturing deformation on a CNT pillar with 10.5 nm a-SiC coating; Image adapted from [3]

23 | INNOVATIVE MATERIALS 3 2018

RESEARCH Electrical interconnect

CNTs have been proposed for many applications in integrated circuits (IC): ranging from transistors and interconnects to sensors and actuators. For these applications it is crucial to integrate CNTs directly alongside electronics. In comparison to traditional approaches using a vertical electrical interconnect access (via) through silicon or polymers, the use of CNTs can provide a higher aspect ratio interconnect with increased density. This is relevant for 3D integration of microelectronics [7]. Development of new CNT based material is of great interest for further applications. To demonstrate the potential of integrating CNT as interconnects in integrated cir-

cuits, we combine our CNT process with a 3D monolithically integrated CMOS process, to successfully realize the first 3D IC’s with CNTs as vias.

Superconductor interconnect

In the research project ‘Super Conducting Nanotubes’, performed within the framework of the 4TU.High-Tech Materials research program ‘New Horizons in designer materials’, vertically aligned CNTs with a superconductor coating are proposed as a superconductive interconnect. Superconductor materials have essentially no electrical resistance below a certain critical temperature, which provides increased performance in integrated circuit devices. The foregoing trend and

demand also drives a need for low-loss superconducting integrated circuits and interconnect structures which enable assembly of superconducting integrated circuits. As is also known, superconducting quantum circuits are a leading candidate technology for large-scale quantum computing. Scalable quantum bits (qubits) integration encounters significant engineering challenges in new materials, fabrication process, and connectivity between the qubits. Superconducting vertical interconnects for 3D qubits integration is in great demand for future quantum computers which require billions of qubits. Since CNTs have a very low coefficient of thermal expansion, high aspect ratio, and are less susceptible to electro-migration, they are used as a vertical interconnect in room temperature microelectronic integration. By mimicking this approach, a solution to fabricate a high aspect ratio superconductive interconnect for cryogenic temperature can be found in the conformal coating of superconductor material on vertically aligned CNT arrays. In that case, the exceptional properties of individual CNTs can provide sufficient toughness and a high aspect ratio matrix. Meanwhile, superconductor coatings not only provide the superconductivity, but can also improve the morphology and density of the CNT array, and ultimately the mechanical properties of the array. Figure 6 shows a photo-lithographically defined CNT pillar, composed of nominally vertical, interwoven, multi-wall CNTs, which are conformably coated with the superconductor material of NbTiN. The proposed structure provides a reliable superconducting interconnect suitable for use in future quantum computers and superconductor applications. Amir Mirza Gheytaghi Email: A.Mirzagheytaghi@tudelft.nl In cooperation with H. van Zeijl, S. Vollebregt, R. Poelma, C. Silvestri, R. Ishihara, G. Q. Zhang, P. M. Sarro, Electronic Components, Technology and Materials (ECTM) - Department of Microelectronics, Delft University of Technology, the Netherlands

Figure 3. CNT array synthetized on top of the suspended MEMS structure. (a) MEMS structure that can be heated up by Joule heating. (b) Tip of a high aspect ratio CNTs; (c) CNTs structure called single micropin; (d) Multi-pin configuration. (e) Infrared thermal maps of the micropin configuration. (f) Thermal interposer made of coated high aspect ratio CNTs integrated in epoxy molding compound; Image adapted from [4] and [5]

24 | INNOVATIVE MATERIALS 3 2018

RESEARCH References: [1] S Vollebregt, et al., ‘Carbon nanotube vertical interconnects fabricated at temperatures as low as 350 °C’, Carbon, Vol. 71, 249-256, 2014. 10.1016/j.carbon.2014.01.035 [2] RH Poelma, et al., ‘Tailoring the Mechanical Properties of High‐Aspect‐Ratio Carbon Nanotube Arrays using Amorphous Silicon Carbide Coatings’, Advanced Functional Materials 24 (36), 5737–5744, 2014. 10.1002/ adfm.201400693 [3] RH Poelma, et al., ‘Effects of nanostructure and coating on the mechanics of carbon nanotube arrays’, Advanced Functional Materials 26 (8), 1233-1242, 2016. 10.1002/adfm.201503673 Figure 4. (a) Fabricated stretchable Fresnel lens containing 2 × 2 lens units, (b) Optical microscope image of one lens, (c) Tilted SEM image of the diffractive CNT pattern, the inset shows a close up view of the vertically aligned CNT, (d) SEM image of the CNT with the PDMS percolated thoroughly into the CNT bundles; Image adapted from [6]

[4] C Silvestri, et al., ‘Thermal characterization of carbon nanotube foam using MEMS microhotplates and thermographic analysis’, Nanoscale 8 (15), 82668275, 2016. 10.1039/C6NR00745G [5] C Silvestri, et al., ‘Effects of Conformal Nanoscale Coatings on Thermal Performance of Vertically Aligned Carbon Nanotubes’, Small 14 (20), 1800614, 2018. 10.1002/smll.201800614 [6] X Li, et al., ‘Stretchable binary Fresnel lens for focus tuning’, Scientific reports 6, 25348, 2016. 10.1038/srep25348 [7] S Vollebregt, R Ishihara, ‘The direct growth of carbon nanotubes as vertical interconnects in 3D integrated circuits’, Carbon, Vol. 96, Pages 332-338, 2016. 10.1016/j.carbon.2015.09.071

Figure 5. Wafer containing the 3D devices: cross-section of two-layer showing the active areas and CNT via; Image adapted from [7]

Parts of this research have been performed within the framework of the 4TU. High-Tech Materials research program ‘New Horizons in designer materials’ (www.4tu.nl/htm). The project page can be found here: https://www.4tu.nl/htm/en/new-horizons/super-conducting-nanotubes/

Figure 6. Coated CNT pillar as a superconductor interconnect

25 | INNOVATIVE MATERIALS 3 2018

AGENDA Utech Europe 29 - 31 May 2018, Maastricht http://www.utecheurope.eu

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26 | INNOVATIVE MATERIALS 3 2018

INNOVATIEVE MATERIALEN 3 2018

Voeg informatie toe aan de Kennisbank Biobased Bouwen De Biobased Economy speelt een belangrijke rol in de duurzame ontwikkeling van Nederland en biedt nieuwe kansen voor het bedrijfsleven. Via de kennisbank kunt u kennis vergaren en delen over de beschikbaarheid en toepassingsmogelijkheden van biobased materialen, producten en bouwconcepten. Samen versterken we zo de biobased economie. Ruim dertig partijen in de bouwsector ondertekenden de green deal biobased bouwen. Deze producenten, architecten, adviseurs en kennisinstellingen delen hun kennis rond kansrijke mogelijkheden van biobased bouwen. Ook de ministeries van Binnenlandse Zaken (Wonen en Rijksdienst), Economische Zaken, en Infrastructuur en Milieu ondersteunen de green deal. Bouw ook mee aan de biobased economie en voeg uw project- of productbeschrijvingen toe aan deze kennisbank. Kijk op www.biobasedbouwen.nl voor meer informatie>

27 | INNOVATIEVE MATERIALEN 3 2018

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