Istraživanja i projektovanja za privredu - Research and Design in Commerce and Industry 4(2010)8

CONTENTS

Dr Stevan Maksimović, Marija Blažić, Mirko Maksimović DESIGN OF CONSTRUCTIONS WITH RESPECTS TO FATIGUE AND FRACTURE MECHANICS

181- 188

Christian Sahr, Lutz Berger 189 - 196 INTERACTION CHAINS OF ENERGY ABSORPTION

Lutz Eckstein, Sven Faßbender, Micha Lesemann, Leif Ickert, Bastian Hartmann, Markus Bröckerhoff 197 - 204 “A CAR FOR EVERYONE“- THE WINNING CONCEPT OF THE INTERNATIONAL FORD MODEL T CHALLENGE

Dr Vladimir Popović, dr Branko Vasić, dr Dejan Curović A POSSIBLE ANSWER TO THE QUESTION: 205 - 214 WHAT IS ASSET MANAGEMENT? Mr Rade Vasiljević HIGHER LEVELS OF MODELING BASED ON 215 - 221 INVENTOR SOFTWARE EVENTS

222

EVENTS REVIEW

224

BOOK RECOMMENDATION

227

INSTRUCTIONS FOR AUTHORS

228

EDITORIAL AND ABSTRACTS IN SERBIAN LANGUAGE 230 - 235

Institute for research and design in commerce & industry, Belgrade. All rights reserved.

Research and design in commerce & industry 8(2010)4

IMPRESSUM Naučno-stručni časopis ISTRAŽIVANJA I PROJEKTOVANJA ZA PRIVREDU Journal RESEARCH AND DESIGN IN COMMERCE & INDUSTRY The journal publishes original and review articles covering the concept of technical science, energy and environment, industrial engineering, quality management and other realted sciencies. The Journal follows new trends and progress proven practice in listed fields, thus creating a unique forum for interdisciplinary or multidisciplinary dialogue.

All published articles are indexed throught international abstract base, Elsevier Bibliographic Databases that includes EMBASE, Compendex, GEOBASE, EMBiology, Elsevier BIOBASE, FLUIDEX i SCOPUS. Ministry of Science and technology development of Republic of Serbia admitted the Journal Research and design for commerce and industry in a list of reference journals.

Publisher Institute for research and design in commerce and industry www.iipp.rs For publisher: Prof. dr Branko Vasić

Copublisher Faculty of transport and traffic engineering – Belgrade University www.sf.bg.ac.rs

International Editorial Board Prof. dr Robert Bjeković, Germany; Prof. dr Jozef Aronov, Russia; Dr Jezdimir Knežević, England; Dr Nebojša Kovačević, England; Adam Zielinski, Poland; Doc. dr Miloš Knežević, Montenegro; Dr Vladimir Buljak, Italy; MSc Siniša Vidović, USA.

For copublisher: Prof. dr Slobodan Gvozdenović

Publishing Council Editor in Chief Prof. dr Jovan Todorović Assistant Editor Dr Predrag Uskoković

Editorial Board Prof. dr Jovan Todorović, Faculty of mechanical engineering, Belgrade; Dr Predrag Uskoković, Belgrade Waterworks and Sewerage, Belgrade; Prof. dr Gradimir Danon, Faculty of forestry, Belgrade; Doc. dr Dušan Milutinović, Institute for transport and traffic CIP, Belgrade; Mr Đorđe Milosavljević, CPI - Process engineering center, Belgrade; Prof. dr Miodrag Zec, Faculty of philosophy, Belgrade; Prof. dr Nenad Đajić, Mining and Geology Faculty, Belgrade; Prof. dr Vlastimir Dedović, Faculty of transport and traffic engeneering, Belgrade; Dr Dejan Curović, Faculty of mechanical engineering, Belgrade; Doc. dr Vladimir Popović, Faculty of mechanical engineering, Belgrade.

ISSN 1451-4117 UDC 33 Papers are indexed by SCOPUS Journal Research and design for commerce and industry is also available on http://iipp.rs/casopis.rs

Nebojša Divljan, Delta Generali, Belgrade; Prof. dr Miloš Nedeljković, Faculty of mechanical engineering, Belgrade; Milutin Ignjatović, Institute for transport and traffic CIP, Belgrade; Dragan Belić, Transport company “Lasta”, Belgrade; Dr Miljko Kokić, Zastava, Kragujevac; Dr Zdravko Milovanović, Faculty of mechanical engineering, Banja Luka; Dr Drago Šerović, Adriatic Shipyard, Bijela; Vladimir Taušanović, Belgrade Waterworks and Sewerage, Belgrade; Nenad Jankov, Power plant Kostolac B, Kostolac; Ljubiša Vuletić, National Bank of Serbia, Belgrade; Dušan Đurašević, Euro Sumar, Belgrade.

Editorial Office Nada Stanojević, Aleksandra Stevanić, Miloš Vasić, Miloš Dimitrijević, Institute IIPP, Belgrade; Bojan Mančić, Ivana Spasojević, Nikola Đurić, Faculty of mechanical engineering, Belgrade.

Printed by: R - print, Beograd Design and prepress: IIPP Research and design in commerce & industry 8(2010)4

EDITORIAL Key disproportions in Serbia and sustainable development Unfortunately, observed by the key segments, Serbia is still incomplete state with many open questions of territorial organization, political model and economic mechanism that could fund sustainable development and establish a new framework of the value system in society. Long time disposal of real and complete reforms led to the accumulation of many disparities of which few can be mentioned: First, the disproportion between total production and inappropriate increase of expenditure has created a growing gap that is covered by donations, remittances, privatization incomes, the new credit lines of state, public and private companies, citizens and high rate of inflation. The ruling establishment has finally Prof. dr Miodrag Zec acknowledged that the model based on the growth of consumption „has exhausted its possibilities“ and that is wrong and unsustainable in the long run. Knowing that the level of industrial production recorded in 2009 is about 50% of the level reached in 1990 is more than dramatic. For a country of our size, location and available resources seems it is devastating to know that industry participates in the creation of GDP with less than one-fifth.

Second, the disproportion between domestic capital accumulation and the level of necessary investments takes to the postponement of investments and when this is impossible, it leads to the new borrowing (loans) under much more unfavourable conditions. The crisis of domestic capital accumulation, previously ascribed to the strategic weaknesses of social ownership concept, continues even after the privatization of the economy, which shows that lack of tendency for savings (accumulation) apart of system has an endemic character also. Main turn-over in society will occur when saving becomes the cornerstone of public and private virtue, and when inflation devaluation of savings and struggle for profit out of debt are eliminated.

Third, the disproportion between imports and exports creates unsustainable gap that is covered by new credit lines and pressure to maintain the exchange rate. This continues to create the inability of development of domestic production and, in the absence of new capital inflows, seriously increases the total public foreign debt, puts the pressure on the credit ratings, dramatizes the state of foreign exchange reserves and threatens the countries external liquidity.

Fourth, the disproportion between the active and dependent population is constantly getting worse even though population growth has been declining (from 30,000 to 45,000 per year). In our society comes to the collapses biological potential because the growth in the number of dependent population is not the result of high fertility (population growth up to 18 years), but the growth of large contingent of dependent population that is in their best working years (18 to 50 years).

Fifth, the disproportion between the employed and unemployed, both aggregate and structural, together with actual rate of unemployment of about 20%, departure of educated people abroad and unsatisfactory qualification structure of the labour market, raises the question who will work if investments ever come in the real sector (industry).

Sixth, the disproportion between the administration and production sector combined with reward system, suggests to the most creative part of the population to focus on the job opportunities outside the industry.

Seventh, the disproportion between the employees in non-exchange sector (banks, shops, services) and exchange sector (industry and agriculture) further draws the most talented students of natural sciences (physics, mathematics, technology) to the non-exchange sector that does not contribute to the production and export growth, but to the sale of someone else’s money and other people’s goods on the domestic market.

Institute for research and design in commerce & industry, Belgrade. All rights reserved.

Research and design in commerce & industry 8(2010)4

Eighth, the disproportion between the number of employees (especially in the exchange sector) and the number of retired people, in the absence of the pension funds capital, requires constant intervention from the budget of the pension system, which leads to the unsustainability of the pension system and the entire second set of acquired rights.

Ninth, disparities between developed and developing regions are increasing despite the fact that for the last 60 years an intensive policy of balanced regional development was present. For that reason a huge budget funds have been spent. In the given circumstances, problems of regional development reflect the politics and from economic become state and territorial issue.

Tenth, the disproportion between the ultra-wealthy and ultra-poor in Serbia is more drastic than in the rest of Europe, including the neighbouring countries where the burning question is not size of the wealth (although it is extensive and acquired with the use of defect or intent of the system) but the depth of poverty that can permanently destabilize sustainable development. In such circumstances the pressure to the redistribution of existing assets can push into the background creation of the conditions for getting out of poverty by creating new wealth. Without assumptions that mechanism of creating a new „nation wealth“ should replace already implemented pattern for redistribution of existing wealth, social stability will not be achieved and consequently no economic prosperity can be expected. Correction of the tax system and incentives for productive investments is the assumption for change of the active capital portfolio of individuals, companies and state. In the same time, such environment is a basis for rational economic and socially acceptable political system.

Serbian society has to deal with continuous accumulation of listed disparities and to take radical steps to stop and reverse them. There is no doubt that the root of the turn for a better and basis of sustainable development must be change of the economic model and measures of current economic policy. Serbia, as a small country, can improve its place in the world economy only by increasing production, reducing current consumption and directing so formed surplus in the capital investments.

Such an approach opens the way to a positive trade balance and creates the basis for the gradual reduction of external debt. Creation of new GDP structure (growth in production and export) and new principles of its distribution (favouring savings and investment as opposed to current spending) will create the basis for changing the ratio of active and dependent population, a new social configuration and turn over towards even regional development. In the new situations, it is likely to expect a change in demographic trends or more radical immigration of the working population rather than emigration. Continuation of previous trends where all the qualitative parameters of development have been declining, where the reduction of the population is accompanied by high unemployment of young and educated people and their emigration, is undoubtedly a sign of deep disturbance and alarm for urgent measures to major changes. The new form of economic development demands a new value concept of society as a whole, which will acquire the assumption of rational economic model and cost-effective and functional state.

Prof. dr Miodrag Zec

Research and design in commerce & industry 8(2010)4

Paper number: 8(2010)3,184, 181-188

DESIGN OF CONSTRUCTIONS WITH RESPECTS TO FATIGUE AND FRACTURE MECHANICS Dr Stevan Maksimović * Military Technical Institute, Belgrade Marija Blažić Military Technical Institute, Belgrade Mirko Maksimović Belgrade waterworks and sewerage An attention in this paper is focused on developing computation procedures during design of flight structures with respects fatigue and fracture mechanics Here are developed analytic expressions for the stress intensity factor (SIF) in 3-D solid type structural components for crack growth analyses.

Damages of structural components are modeled with semi-elliptic surface cracks. Structural components are under cyclic loads and load spectra. Results of presented analytic model of FIN are compared with finite element results. Good agreement between presented analytic and finite element results is obtained. Strength analysis with respect static fracture mechanics is illustrated on nose landing gear problem of light training aircraft.

Key words: Fatigue of structure, Fracture mechanics, Crack in 3-D solids, Analytic model, Life estimation, Metal structures.

INTRODUCTION Structural integrity analysis of aging aircraft is a critical necessity in view of the increasing numbers of such aircraft in general aviation, the airlains and the military. Damage tolerance analysis can be used to assess the remaining life of aircraft in service. In a damage tolerant design/analysis initial cracks are considered to be present at each of the critical components in the structure and these initial cracks are allowed to grow. At each stage in the life of the structure the current crack lengths are evaluated and the associated stress intensity factors K are computed. These values of K are then used to evaluate both the residual strength and the crack growth rate associated with each crack. In aerospace industry the initial cracks tend to be quite small. Thus at each stage of the life of structural components it is necessary to analyse of a complex two-dimensional (2-D) or three-dimensional (3-D) crack under arbitrary loading. Due to the singularity along crack front this requires to use singular finite elements.

Design approach of structural components with initial proposed cracks at the potential critical

area of complex construction is known as damage tolerance approach [1]. In practical design numerical simulations based on finite element method (FEM) are efficient method do determine critical locations at structural components with respect the fatigue and fracture mechanics.

Residual life estimations of damaged structural components under cyclic loading requires determination of various fracture mechanics parameters [2,3,6-9]. Key parameter in fracture mechanics analysis is stress intensity parameter K. In a damage tolerance design of thin-walled structures the initial cracks are proposed through the thickness of structural components. However in situations of robust structural components and constructions initial cracks must be defined as surface cracks. In aircraft constructions, typical “3-D” solid with initial surface damages are structures of landing gears and wing/fuselage joints.

In contrast to the thin-walled construction considerable complex problem represent defining SIF in the analytic form for 3-D structure. There exist a lot of attemption to derive analytic expressions of SIF to semi-elliptic surface crack [10,12,15].

In this work one analytic model for determination

* Military Technical Institute, Ratka Resanovića 1, Belgrade; s.maksimovic@nadlanu.com

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Dr Stevan Maksimovic and etc. - Design of constructions with respects to fatigue and fracture machanics

SIF for “3-D” semi-elliptic surface crack is proposed. For determination of “3-D” semi-elliptic surface crack can be used finite element method (FEM). For that purpose are used special 3-D singular finite elements. Singular finite elements are very accurate method for SIF computation, but crack growth analysis is very complex. On because of that reason in this work an attention is focused to deriving quality analytic expressions for determination of stress intensity factors and crack growth models.

(2)

where previous coefficient are defined as:

(3)

BASIC RELATIONS TO CRACK GROWTH ANALYSIS

(4)

In the residual life estimation of structural components with respects fatigue and fracture mechanics can be used various crack growth models. For this purpose for the fatigue crack growth programs are the incorporation of the ability to read aircraft spectra of unlimited size, generation of common aircraft fatigue load blocks and the incorporation of crack-growth models which include load-interaction effects such as retardation due to overloads and acceleration due to underloads. In this investigation Forman and Mettu [4] crack-growth model is used. This crack-growth model is incorporated im many commercial fatigue life softwate codes. This crack growth model is defined in the next form:

(1)

where N is the number of applied fatique cycles a - crack lenght ) - is the stress ratio R (=

(5) (6) In these equations is plane stress/strain constraint factor and is the ratio of the maximum applied stress to the flow stress.

0

DETERMINATION OF STRESS INTENSITY FACTORS FOR SEMI-ELLIPTIC SURFACE CRACKS For crack growth analysis, in accordance of eq.

(1), it is necessary to be known stress intensity factor (SIF), K, in the analytic form. Here is considered problem threedimensional structural elements with semi-elliptic surface crack, Fig.1.

For determination of SIF at critical locations, points A and B in Fig. 1, here ‘’layered’’ model [5,14] is used.

- is the stress intensity factor (SIF) range C, n, p, q - are empirically determined constants under cyclic loads, f - is the crack opening function - is the threshold stress intensity factor and Kc is the critical stress intensity factor. This equation provides a direct formulation of the stress-ratio effect. Newman is defined the crack opening function in form:

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Figure 1. part one - Model 3-D solid with surface semi-elliptic crack Research and design in commerce & industry 8(2010)4, 184

Dr Stevan Maksimovic and etc. - Design of constructions with respects to fatigue and fracture machanics

(11) where and are the crack lengths and thickness are defined in Fig. 1, until Aij and Bij represent corresponding the influence functions.

NUMERICAL SIMULATIONS

Figure 1. part two - Model 3-D solid with surface semi-elliptic crack

This model divide solid to layers in horizontal and vertical planes making two systems in which: layers in plane x -y represent conventional plates with central cracks and layers in plane y-z represent plates with edge cracks.

This systems are conjugated across distribution of pressure p*, acting to surfaces of crack of each system and causing that these displacements of two systems need to be equal. Using pressure distribution to surface of crack, the stress intensity factors at the points A and B may be determined as: (7) (8)

Function

that is used in previous

relations is general influence of function for central crack, gck, or edge crack, gip . The influence function is defined as: (9) where K( is the stress intensity factor for some load distributions which act to crack length , and v is the displacement of crack surface at any point x. Without the complete theoretical consideration here are given final expressions for stress intensity factors for semielliptic surface crack at points A and B in accordance to Fig.1, (10)

Research and design in commerce & industry 8(2010)4,184

To illustrate numerical simulations to residual life estimations and strength analysis with fracture mechanics here are numerical examples are included.

Example 1: Crack growth analysis Analytic expressions for SIF’s of semi-elliptic crack to surface of 3-D solid, defined in previous consideration and crack growth model, are incorporated in software package “LOM-3”[11].

To illustrate numerical simulation of crack growth in 3-D solids here is included problem of thick plate with surface crack under tension cyclic loading. Here is established analytic computation procedure that is illustrated for crack growth analysis of 3-D solid under load spectra. Crack growth analysis under load spectra is defined in Table 1.

Table 1. Load spectra

Ni 6000 6000

Smin [MPa] 0 100

Smax [MPa] 500 400

Crack growth analysis made to the next material and geometric properties of panel with semi-elliptic surface crack, as shown in Fig.1.

Width of crack Height of crack Thickness Width Parisso’s coef.

Paris exsponent Fracture toughness

a = .100E-02 [m] c = .100E-02 [m] t = .200E-01 [m] W = .200E-01 [m] Cp = .300E-10 np = .250E+01 Kic = .500E+02

Table 2. Širenje 3-D prskotine a [m]

N (F15A)

N (F15B)

0.001 0.00E+00 0.001 0.0013 4.95E+03 0.0013 0.0014 6.00E+03 0.0015

N (german)

a [m]

0.00E+00 0.001 3.91E+03 0.0013 6.00E+03 0.0015

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Dr Stevan Maksimovic and etc. - Design of constructions with respects to fatigue and fracture machanics

0.0015 0.0018 0.0021 0.0021 0.0023 0.0026 0.0029 0.0032

1.20E+04 1.51E+04 1.77E+04 1.80E+04 2.40E+04 2.59E+04 2.75E+04 2.89E+04

0.0017 0.0019 0.0022 0.0025 0.0026 0.0029 0.003 0.0033

1.20E+04 1.42E+04 1.60E+04 1.75E+04 1.80E+04 2.25E+04 2.40E+04 2.51E+04

0.0017 0.002 0.0023 0.0025 0.0027 0.003 0.0031 0.0034

0.0034 0.0037 0.0038 0.0041 0.0044 0.0047 0.0049 0.0052

3.00E+04 3.42E+04 3.60E+04 3.70E+04 3.79E+04 3.88E+04 3.96E+04 4.03E+04

0.0036 0.0038 0.0041 0.0044 0.0047 0.005 0.0051 0.0054

2.60E+04 2.69E+04 2.77E+04 2.84E+04 2.90E+04 2.96E+04 3.00E+04 3.19E+04

0.0037 0.004 0.0042 0.0045 0.0048 0.0051 0.0054

N (cycles) Figure 2. Results of the crack gowth analysis under load spectra

In Fig. 2 are shown relations between crack lengths a and number of cycles N during crack propagation. Curve denoted as Anal-A and AnalB represent crack growth of points A and B of semi-elliptic surface cracks using analtic expressions (10) and (11) for SIF with one side and crack growth model (1) with other side. Curve denoted as MKE-B represents crack growth of point B where SIF is defined using approximations of FEM. In table 2 are given the complete crack growth resultats. The complete procedure for determination of SIF based on FE aproximations is illustrated in reference [8]. This procedure is based on using 3-D singular finite elements to determine SIF for several successive

184

crack lengths and for these are established analytic expression in polynomial form for stress intensity factor (SIF) and then is used in crack growth analysis.

This method for determination of SIF’s using special 3-D singular finite elements is usefull and reliable method but very complicated tool. Good agreement of crack growth results between analytic and proposed finite element approximations (MKE-B) at point B is obtained. It means that proposed analytic approach for detrrmination of SIF during crack growth is very accurate and efficient method. It is important that this analytic approach can be used instead of very complex finite element approximations to crack growth Research and design in commerce & industry 8(2010)4, 184

Dr Stevan Maksimovic and etc. - Design of constructions with respects to fatigue and fracture machanics

modeling at the 3-D cracked structural components.

Example 2: Numerical simulations to problems with surface cracks Analytic expressions of SIF’s for semi-elliptic surface crack at 3-D solids, defined in previous chapters, and different crack growth models are included in software package “LOM-3”[11]. Characteristic problem to application with respects fatigue and fracture mechanics of surface cracked problems is aircraft nose landing gear, Fig. 3. It means that numerical simulations can be used to determine SIF’s using singular finite elements for different shapes of surface damages such as aircraft nose landing gear, Fig. 3, with one side and for crack growth analysis of surface cracks with other side.

Design condition with respects to „static“ fracture mechanics is that SIF be lower than critical stress intensity factor or that reserve factor of safety (R.F) be larger than 1: (12) where: KIC is the fracture toughness of material, KI is the stress intensity factor, and j represents load level coefficient.

Figure 4. Finite element model of light aircraft nose landing gear

Determination of SIF using FEM to static part of nose landing gear For „static“ strength fracture mechanics analysis precise deterination of stress intensity factors is necessary. After determination of critical location to structural element using FEM with respects fracture mechanics to static part of nose landing gear, Fig. 4, it is necessary to propose initial surface crack in this location. Critical location to static part nose landing gear (steel tube), Fig 5.a. For determination of the stress intensity factors here two FE models are used: 3-D model FEM (Fig. 6) tube with semi-elliptic crack as shown in Fig. 5.b.

Figure 3. Structural model to nose landing gear of light training aircraft

In Fig. 4 are shown results of stress distributions to aircraft nose landing gear using finite element software MSC/NASTRAN for one load case. Using FEM here is defined critical location with respects fatigue and fracture mechanics analysis, i.e zone of maximal stresses to static part of nose landing gear, Fig. 4.

Research and design in commerce & industry 8(2010)4,184

Figure 5.a. Geometry of static part under tension load (σ=10 daN/mm2)

Material: Če 1.7734.4 KIC=190 daN/mm3/2

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Dr Stevan Maksimovic and etc. - Design of constructions with respects to fatigue and fracture machanics

Figure 5.b. shape of semi-elliptic surface crack

Figure 6. 3-D FEM model of static part to landing gear with semi-elliptic surface crack

Figure 7. Detail of stress distributions around surface crack to static part of nose landing gear

crack is defined through the thickness of wall, as shown in Fig. 9.

Figure 8. Detail of the stress distributions to zone semi-elliptic surface crack to static part of nose landing gear (a/c=0.4)

In figures 7 and 8 are given detail stress distributions near semi-elliptic surface crack.

Next to modeling static part using FEM with semi-elliptic surface crack, Fig. 6 to 8, carried out modeling with 2-D finite elements too, where

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Figure 9. 2-D FEM model to static part with crack throught the thickness Research and design in commerce & industry 8(2010)4, 184

Dr Stevan Maksimovic and etc. - Design of constructions with respects to fatigue and fracture machanics

Table 3. Values of SIF for cracks at static part of landing gear

Shape of crack c=2.75 mm

elliptic a=2.25 mm

KIA (daN/mm3/2) 21.28

through the thickness c=7 mm

eliptična a=2.25 mm

Obtained results for SIF’s, Table 3, illustrates that the last model is conservative and can be used, due its simplicity for modeling, in preliminary design [14]. First model, with surface semielliptical crack is real model and can be used in precise analyses to structural components with respects fracture mechanics.

CONCLUSIONS In this investigation analytic method for determination of the stress intensity factors to surface cracks at the 3-D solid structural elements is established. Derived analytic expressions for stress intensity factors can be used for strength analyzes with respects fracture mechanics to: aircraft structural elements, fuel tanks under pressures, in ship design and many other structures. Primary attention of this paper is to establish analytic expressions of SIF’s for surface crack which can be effective used in crack growth propagations and residual life estimations.. Accuracy of derived analytic expressions for SIF’s are compared with finite element approximations. Good agreement analytic with finite element results is obtained in domains „static“ fracture mechanics and crack growth analyses.

Practical in this investigation the efficient and accurate analytic computation procedure for crack growth analysis with initial surface cracks of robust structural components and constructions is proposed. This procedure achieves efficient approach of residual life estimation of damaged 3-D structural components under cyclic loading Research and design in commerce & industry 8(2010)4,184

28.56 30.57

40.25

through the thickness In Table 3 are given the complete results for SIF’s to surface crack, with one side, and for crack through the thickness, with other side. As expected, here are obtained larger values of stress intensity factors for through the thickness then in case of semi-elliptic surface crack.

KIB (daN/mm3/2)

34.5 56.8

under cyclic loading and general load spectra.

The complete computation procedure for crack growth analysis is illustrated to aircraft nose landing gears. Procedure is based on using finite element method to determine critical locations with respects to fatigue and fracture mechanics with one side and to use analytic expressions for determination of SIF’s and residual life of structural components with other side.

REFERENCES 1) “Airplane Damage Tolerance Requirements”, MIL-A-83444, Air Force Aeronautical Systems Division, July 1974.

2) Broek, D., Elementary Engineering Fracture Mechanics, 4th edition, Nijhoff, 1985 3) Broek, D., The Practical Uses of Fracture Mechanics, Kluwer Academic Publishers, 1989.

4) Forman, R. G., and Mettu, S. R., “Behavior of Surface and Corner Cracks Subjected to Tensile and Bending Loads in Ti-6Al-4V Alloy,” Fracture Mechanics: Twenty-second Symposium, Vol. 1, ASTM STP 1131, H. A. Ernst, A. Saxena, and D. L., McDowell, eds., American Society for Testing and Materials, Philadelphia, 1992, pp. 519-546.

5) Fujimoto, W.T., and Mettu, Sambi, A, Weight Function Approach for Tracking the Growth of Surface and Radial Cracks through Residual Stress Fields or Bi-Variant Stress Fields, ASIP 2000, San Antonio, Dec. 2000.

6) Maksimović, K., Nikolić-Stanojević, V., Maksimović, S., MODELING OF THE SURFACE CRACKS AND FATIGUE LIFE ESTIMATION, ECF 16, 16th European Conference of Fracture, ECF 16, Alexandroupolis, Grčka, 2006

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Dr Stevan Maksimovic and etc. - Design of constructions with respects to fatigue and fracture machanics

7) Maksimović, S., Boljanović, S., Orović, V., Komnenović, M., Fatigue Life Analysis of Damaged Structural Components Using Strain Energy Density Method, 17th European Conference on Fracture – Multilevel Approach to Fracture of Materials, Components and Structures, Brno, Czech Republic, September 3-5, 2008.

8) Maksimović, S., Fatigue Life Analysis of Aircraft Structural Components, Scientific Technical Review, Vol. LV, No. 1, 2005,pp. 29-33.

9) Maksimović, K., FATIGUE CRACK GROWTH ANALYSIS OF DAMAGED STRUCTURAL COMPONENTS UNDER MODE-I AND MIXED MODES, Scientific Technical Review, Vol. LIX Br. 1, 2009, pp. 35-40.

10) Maksimović, K., Strength analysis of constructions using damage tolerance approach under dynamic loading (In Serbian), Master Thesis, Faculty of Mechanical Engineering, University of Kragujevac, 2003.

11) Maksimović, S. i Mladenović, J., “LOM-3” Software package for fatigue strength analysis under general load spctra, VTI Žarkovo, 2001.

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12) Newman, Jr., J. C. and Raju, I. S., “Prediction of Fatigue Crack-Growth Patterns and Lives in Three-Dimensional Cracked Bodies,” Advances in Fracture Research (Fracture 84), Sixth International Conference on Fracture, Vol 3, 1984, pp. 1597-1608.

13) Orynyak, I.V., and Borodi, M.V., Point Weight Function Method Application for Semi-Elliptical Mode I Cracks, International Journal of Fracture, 70, No. 2, 117-124, 1994-1995..

14) Ognjanović M., Design in mechanical engineering - Multidisciplinary approach, Journal Istraživanja i projektovanja za privredu, No. 20, 2008 15) Raju, I and Neuman, J.C, Improved Stress Intensity Factors for Semi-Elliptical Surface Cracks in Finite-Thickness Plates, NASA TN X-7285, August 1977 Paper sent to revision: 06.09.2010.

Paper ready for publication: 30.11.2010.

Research and design in commerce & industry 8(2010)4, 184

Paper number: 8(2010)3,185, 189-196

INTERACTION CHAINS OF ENERGY ABSORPTION Christian Sahr* Institute of Automotive Engineering, Germany Lutz Berger Institute of Automotive Engineering, Germany The occupant protection and especially the pedestrian protection are getting more and more important since several years. The reason is the insufficient safety of the pedestrian against severe injuries during the impact with vehicles. For the reduction of injuries and their severity, design changes within the frontal structure are necessary to absorb energy and to reduce the forces and accelerations on pedestrians. Therefore more and more of such structures for energy absorption are considered that are often designed with different materials like highly porous foams as well as energy absorbers with plastic deformation behaviour such as egg-box structures. Combinations of such parts are interacting under crash load e.g. the bumper system. For the layout of new protection systems, it is necessary to predict deformation behaviour and force level of these “interaction chains�.

The main purpose of the present study is, together with Institute for composites in Kaiser-slautern, to detect and quantify the interactions among structural components in complicated systems, which take place during low-energy-impact events. Since these interactions often lead to deviation between experimental and simulation results, the accuracy of forecast of the crash simulations will be increased as a consequence of this investigations.

The energy absorbing system, investigated in this study, represents an interaction chain of different constituent components: EPP foam, a polymer eggbox structure, steel and alumi-num sheets.

This interaction chain and its constituent components are investigated experi-mentally and further modelled with finite element code LS-Dyna. Own experimental material data is used to validate the material models.

Keywords: Materials engineering, Composites, EPP-foam, Eggbox, Numerical simulation, Energy ab-sorption, Validation, Modelling, Test, Pedestrian protection, Complex impact processes INTRODUCTION Besides the occupants protection, the pedestrian protection especially gained importance within the last few years. By now pedestrians stand for more than 15 % of all casualties of the European road traffic [BUN03]. In order to improve pedestrian safety, Phase I of the EU Directive 2003/102/EC came into effect on the 1st October 2005, which regulates a test of the structure behaviour of the vehicle front, whilst using a body impact testing procedure. On 14th January 2009 a further regulation 2009/78 EC was started with aggravated requirements. In order to reduce the injuries of pedestrians, constructive changes in the vehicle front struc-ture are necessary, to absorb energy and to decrease

the forces and accelerations that have an impact on the pedestrian. For these reasons, the usage of energy absorbed structures is required, these are mostly accomplished in multi-material-design. Next to highly porous foams, components with distinctive malleable deformation behaviour are used, to which the so called eggbox structure belongs to. Combinations of such structures correlate with each other when attaching crash encumbrances. It is necessary to be able to predict the deforma-tion behaviour and strength level of these interactions, in order to design new protective systems. Although those single components were validated in the simulation and are easy to describe, it is common that notable differences occur between calculation and test for the whole interaction chain, due to the very different stiff-

Institute of Automotive Engineering - RWTH Aachen University, Steinbachstr. 7, 52074 Aachen; sahr@ika.rwth-aachen.de

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ness of the components. Impact proc-esses with interaction of various components on a low energy level are in particular hard to describe.

MOTIVATION Throughout the car are areas, where various materials contribute jointly to the energy ab-sorption. In this project, an impact chain is defined as a combination of at least two compo-nents that interact. An example of an impact chain, consisting of four components, can be seen in Figure 1. This is constructed of EPP-foam (Neopolen

P from BASF AG), a sheet of aluminium, an eggbox structure consisting of Acrylnitril-StyrolAcrylester (ASA) and a steel plate. Exemplary for a realization, is the energy absorbed impact chain on the right side, which made of a steel cross member, a foam and a plastic covering.

At almost all collusion scenarios the described impact chains occur, when the single compo-nents of the whole chain lie partly parallel partly serial in the distribution of forces. During the impact process, the arrangements, thus the interactions can change between the involved components.

Plastic cover EA - foam Steel cross member Steel Eggbox structure Aluminium EPP -foam

Figure 1. Architecture of an impact chain (left), Example of a vehicle front [ERN00] (right)

Aim of the conducted research within the DFGproject “Evaluation of the cross impacts of structure elements of complex impact processes” was to determine the interactions between adjacent components, which occurred during the impact processes, to improve the predict-ability of FEsimulations with a comparison of corresponding tests, and to grasp coinciden-tally the boundaries of the calculation for suitable comparable loading conditions. For the analysis a simplified scenario was considered, which is likely to occur with a leg impact against a bumper or a head impact on the bonnet.

CHARACTERISATION OF THE MECHANICAL FEATURES The state of the art enables a simulation of the material features of a single component with the precision, which corresponds to the accuracy of measurement of the material test. How-ever, this precision of the depiction of the material features, is not directly contained in the FEM-codes, but refers to an adequate precise selection and calibration of the material mod-els, which are available to the FEM-codes. A comparison be-

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tween the simulation and test requires experimental data. As a very precise depiction was aimed at in the described pro-ject, basic literature was not sufficient. The single components were instead examined with help of the following loading cases.

Material modelling The steel and aluminium material parameters were recorded with the aid of tensile tests for various strain rates, and afterwards depicted with the, for these materials, common material model 24 “MAT_PIECEWISE_LINEAR_PLASTICITY”. The validation of the tensile test took place in a LS-DYNA tensile test model.

The eggbox was manufactured through thermoforming out of Acrylnitril-Styrol-Acrylester (ASA) with a thin top coat of Polycarbonat. As material model the material “MAT_PLASTICITY_¬COMPRESSION_¬TENSION” was chosen by the research partner IVW, in order to depict tensile and pressure curves separately. The needed material parameters of the EPP-foam for the simulation were evaluated at the ika. The validation is described as follows.

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At first the appropriate material models for the simulation of the foam material are chosen and are compared to each other. Most of the available models in LS-Dyna are merely for very specific applications. Whereas others represent more general models, which can be used for a various number of materials. For the EPP foam the LS-Dyna material model 83 “MAT_FU_CHANG_ FOAM� was chosen. The direct input opportunity of the suspense-strain-curves for different strain rates were one reason for choosing the latter.

With this model, the strain rate dependency of the foam material can be considered without restraints. From the experimental researches, results both from quasi-static suspense tests with the strain rates 0,01 1/s, 0,1 1/s and 1 1/s and from dynamic suspense tests with strain the rates

50 1/s, 100 1/s and 180 1/s were available.

The measured raw data in the first instance conditioned for the simulation. Afterwards the tests were simulated for all six strain rates and then validated. Because the strain rates were chosen in a spectrum of quasi-static and highly dynamic weighs, the numeric calculation was able to be conducted with LS-DYNA, which provides both a implicit and a explicit FE-Solver. The material parameters were chosen for a joint model in such a way, which made the ag-gregate deviation minimal in the single simulations. Figure 2 compares exemplary the defer-ment behaviour of the basic alternative and the final alternative after the validation of the deferment behaviour within the test for a strain rate of 50 1/s.

Figure 2. Delay EPP-foam strain rate 50 1/s

The element size is a parameter, which is not only influencing the stability of the calculation, but is also having an impact on the results of the simulation. It turned out that the configura-tion of the fully integrated volume elements for the load cases, produced a further approach to the test curves. Additionally, the occurrence of Hourglass-energy was avoided.

Besides the used element type, the contact definition had a major impact on the stability and the results of the simulation. Contact damping reduced the high frequented oscillations of the contact forces. Such contact oscillations cause instabilities, which especially often occur by con-

tacts with foam. These can be reduced, due to the use of the viscous damping coefficient (VDC).

A value between 40 and 60 is recommended for foams. Furthermore, the scale factor for the time step has to be decreased to 0,66 [DYN06].

The acceleration tests represented in Figure 3, demonstrate the result of the validation for the dynamic and quasi-static tests with respective simulations. On the whole, there are good congruities between tests and calculations after the simulation.

The validation of the foam model was used only for the compression phase, because the LSDyna version used at the beginning of the project

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was, in contrast to the current version 971, not able to define the decompression phase in the model *MAT_FU_CHANG_FOAM iso-lated. The relief phase in the material model is thus determined by the lowest strain rate curve. Therefore, there is a stiffer behaviour in the simulation than

in reality. Relevant for the determination of injury criteria in simulations, exemplary the impact for the foam of a leg impact, is merely the strain phase, not the relief phase. However, this form of validation does not represent a constraint to the generated model.

Figure 3. Overview of the compression tests

Determination of the adhesion and sliding friction coefficients In order to describe the contacts and the already described interactions exactly, the occurring sliding friction coefficients between the different material couples will be determined using various velocities. The surfaces of the metallic materials will be prepared in the following three ways, in order to obtain the different reference values: • •

•

Unmachined: The surface of the steel and aluminium sheets will be used as supplied.

Coarse-sanded: The surface of the metallic components will be sanded with a disc-type sander using a sanding paper with a grain of 40.

Polished: The surface of the sheets will be polished.

The surface of the thermoplastic absorber will be used in the delivered condition, because a surface treatment of the eggbox structure is very elaborate. The surface of the EPP-foam which emerged during the production process will be treated as well. The testing geometry will be generated via milling of the delivered foam

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blocks. In order to obtain measurements of the adhesion and sliding friction coefficients the Institute for composite materials in Kaiser-slautern owns a special testing machine. The determined parameters will be used as starting values for the contact definition and the validation.

Simulation and validation of the interaction chains To be able to reproduce the interaction of complex systems in the simulation, it is necessary to gradually build up a system with increasing complexity. Using the simplest system no considerable interactions should occur, thus a reliable experimental and arithmetical repro-duction can be guaranteed. Subsequently the complexity of the system has to be enhanced as far as the occurring interactions appear in detectable quantity, however the individual effects should still be recognized solely. The interaction chains will be built accordingly to Figure 4.

First of all, four 2-component-interaction-chains will be examined. Followed by two 4-componentinteraction-chains which are composed of the just examined composites.

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Figure 4. Testing matrix

The dynamic strain of the interaction chains takes place by using impacter with plane, semicylinder-shaped and hemispherical impact surface, in order to reflect different impact scenarios. The chosen strain rate of 180 1/s covers up conditions which can occur with collusions with pedestrians on a vehicle front end.

The single testing configurations will be reproduced in the FEM, and the available variation parameters will be amended in a way that the forces and deformations from the simulation correlate to the tests as most as possible. The validation aims to optimally reproduce all tests on the corresponding material with a material model. For example, the aluminium sheet should not only correctly be reproduced in the quasi-static tensile test, but also with all looked at testing velocities and load situations.

In regard to the modelling of the individual components, based on the finite elements, several objectives are aimed at: •

•

The verification of the assumption that the mechanical behaviour of the individual components are reproduced correctly in all load situations.

The preparation of the simulation of the whole interaction chain.

The parameters of the material models will be adopted from the single material validation. The geometric information will be maintained as well as the figures of the element thickness. Static and dynamic contact-friction-coefficients will be deduced from the results of the friction test, but continue to be variation parameters.

The validation process of the 2-component-interaction-chains contains the variation of LS-Dynacontrol-cards, -contact cards and the modelling Research and design in commerce & industry 8(2010)4, 185

technique. In this case modelling tech-nique stands for the modelling of the impactor and the floor. Both can be compiled from surface elements, solid elements or rigidwalls. Due to the good simulation stability, the im-pactor will be modelled using surface elements, and the floor using rigidwalls. During the validation of the interaction chains several contact- and elementtypes will be compared with each other as well.

In the second phase, the 4-component-interaction-chains were build. With the aid of the insights of the 2-component-interaction-chain, the same parameters as beforehand will be varied.

Thereby, the strain rate of the eggbox material has a great influence on the behaviour of the 2-component-functial-chains. The interaction chain eggbox-structure-steel is better reproduced without strain rate dependencies. On the opposite, the results of the 4-component-interaction-chains are better obtained with the latter.

RESULTS The comparison of the carried out tests and simulations of the 2-component-interaction-chains suggest the following results. The interaction chains EPP-foam-aluminium, respec-tively EPPfoam-steel, reveal a good consilience between the simulation and real-life tests. The force level coincides very well, as can be seen in Figure 5.

The force peak at 1 ms in the calculation results from the contact calculation. This peak can be reduced through a stronger damping. However, this does not have an impact on the acceleration process. As described in chapter 4.3, the deviation in the relief phase originates from the foammaterial-model. This phase is not illustrated for the simulation curve in Figure 5.

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Figure 5. Comparison of simulation and test for the interaction chain EPP-steel with a hemi-spherical impactor

The comparison shows the best consilience for the hemispherical impactor. Greater deviations occur for the plane and semi-cylinder-shaped impactor.

The deviations of the interaction chains eggboxstructure-aluminium und eggbox-structure-steel in simulation and test vary with the impactor geometrics. The plane impactor shows the best consilience. Nevertheless, the outcomes for the hemispherical and semi-cylinder shaped impactors, obtained from the FE-Simulation differ from the data obtained from ex-periments. The interaction chain is stiffer, thus the deformation process is a bit shorter on the whole.

This difference in the results can be moderated when modelling the eggbox structure without strain rate dependency. However, the analysis of other boundary conditions and systems indicate that the strain rate dependency of the eggbox materials should not principally be disregarded, as well as indicating that the deviation of the results come from the interactions of the complex system which were not looked at in detail within this study.

In Figure 6 and Figure 7 a video sequence from the test series with a 4-component-interaction-

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chain under the load of the hemispherical impactor is contrasted with the simula-tion results. The EPP-foam-aluminium-eggboxstructure-steelinteraction-chain can be repro-duced very well in the simulation. Little differences in the compression phase originate from the facilitation of the eggbox structure. In particular, the material thickness differences, result-ing from the manufacturing process, and the internal strain of the material are not considered in the simulation.

Furthermore, the comparison, of the deformation behaviour from the visual information of a high-speed-video-measuring with the information from the calculations, is difficult.

In the process of the validation, the following attributes, respectively parameter, appeared to be especially important: • • •

Strain rate dependency of eggbox material, EPP-foam and steel Impactor geometrics Contact definition (especially friction parameters)

Furthermore, it was clearly shown that the order of the interaction chain components, had a major impact on the results.

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t=0

t = 4 ms

t = 8 ms

t = 12 ms

t = 16 ms

t = 20 ms

Figure 6. Test interaction chain EPP-foam aluminium eggbox structure steel

t=0

t = 4 ms

t = 8 ms

t = 12 ms

t = 16 ms

t = 20 ms

Figure 7. Simulation interaction chain EPP-foam aluminium eggbox structure steel Research and design in commerce & industry 8(2010)4,185

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CONCLUSION Within the framework of this study, materials for energy absorption were looked at which interact due to an impact with low energy, for example a vehicle-pedestrian collusion. In order to examine the possibility of being able to predict the interactions of different deforma-tion elements, beforehand conducted real-life tests were simulated using LS-Dyna.

Thereby, three different impacters as well as varied dispositions of the materials (aluminium, steel, EPP-foam, and Acrylnitril-Styrol-Acrylester (ASA)) used for the interaction chain were looked at.

The simulation process initially contained the modelling of individual components and the interaction chains, as well as the conduction of parameters obtained in simple tension-, force- and bending tests into appropriate material models for each of the four materials. The validation of the composites was gradually accomplished, in respective to the previously done experiments, first on the 2-component-interaction-chains and thereafter on the 4-component-interaction chains.

tween simulation and test. The approach of the just described examinations indicates respective boundaries for the simulation capabilities which implies vital importance for the interpretation of calculation results. Despite nowadays opportunities to more detailed modelling of components, as well as new or enlarged material models, fundamental tests to verify simulation results will still be necessary in order to achieve increased prediction accu-racy for complex, interacting systems.

LITERATURE 1) [BUN03]

N.N. - Bundesamt fĂźr Statistik

Statistisches Jahrbuch 2003 1) [DYN06] http://www.dynasupport.com/ Support/helpcenter_view 2) [ERN00] ERNSTBERGER, U “Rohkarosserie und Passive Sicherheit der neuen C-Klasse� - ATZ 7-8, Vieweg Verlag, 2000, Seite 508ff Paper sent to revision: 04.10.2010.

Paper ready for publication: 26.11.2010.

During the validation, the contact and friction parameters, the strain rate dependent material curves and the influence of the impector shapes were identified as most important figures. Furthermore, the facilitated depicted eggbox structure in the simulation, proved to be one of the main reasons for the deviations between the simulations and the tests. The thickness differences and internal strains, resulting from the manufacturing process, were not looked at in the simulation. Moreover, the failure behaviour of the eggbox structure turned out to be significantly, but could not sufficiently be covered by the simulation. Therefore, a detailed examination of these effects has to be ensued, in order to achieve an even better consilience between the results of testing and simulation.

It was principally shown that even if the individual modules of the materials with different stiffnesses were very good to simulate, a fine tuning of chosen material parameters as well as an adjustment of the parameters for the contact calculation, already proved to be neces-sary for interaction chains with two or four components, in order to generate an adequate consilience be-

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Paper number: 8(2010)3,186, 197-204

“A CAR FOR EVERYONE“- THE WINNING CONCEPT OF THE INTERNATIONAL FORD MODEL T CHALLENGE Lutz Eckstein* Institute of Automotive Engineering, Germany Sven Faßbender Institute of Automotive Engineering, Germany Micha Lesemann Institute of Automotive Engineering, Germany Leif Ickert Institute of Automotive Engineering, Germany Bastian Hartmann Institute of Automotive Engineering, Germany Markus Bröckerhoff Institute of Automotive Engineering, Germany A team of the Institut für Kraftfahrzeuge (IKA) of RWTH Aachen University needed only three months in order to develop an innovative vehicle concept which is capable of carrying conventional as well as alternative drivetrain modules thanks to its scalable design – a modern “car for everyone” for the year 2015 with a basic sales price of less than 7000 US dollar.

Keywords: Concept requirements, development of the concept, technical specifications, topology optimisation, drivetrain system INTRODUCTION Over a production duration of 19 years, about 15 million units of the legendary Ford Model T have been sold. The Ford Motor Company has launched the Model T Challenge 2008 under five universities worldwide to celebrate the 100th anniversary of the Tin Lizzy in order to find out the best concepts for a successor.

Figure 1. Ford model T challenge

The demand was to develop a modern Model T in only three months time while being simple, robust, light and compelling. Besides these hard facts, space for at least two passengers, a range of 200 km as well as a maximum basic sales price of 7000 US dollar were required with the latter surely being the hardest challenge.

APPROACH A scientific approach, though inspired by the industrial development process, was chosen for the development of the concept vehicle, Figure 2. Based on the demands that were given for the challenge, the requirements for the vehicle have been analysed. This included a detailed examination of the success factors of the predecessor, the historic Model T, as well as an investigation if and how these could be transferred to a modern car. The scenario analysis revealed further boundary conditions and economic requirements of the relevant markets. The main driver was the very ambitious basic sales price though

Institute of Automotive Engineering - RWTH Aachen University, Steinbachstr. 7, 52074 Aachen; eckstein@ika.rwth-aachen.de

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from which target costs for every module had to be derived using a target cost calculation.

The requirements which had been depicted in the analysis phase were then collected as concept specifications for the definition phase. Based on these, the actual concept development started which was characterised by highly parallel processes and a permanent cost controlling. In order to generate not only concept ideas but technical feasible solutions in the very limited time given, strategies for efficiency increase had to be applied. It was mainly the parallelisation of component development and styling, traditionally an up-front process, which significantly saved time.

The rough styling was decided based on hand sketches while the detailed surface construction was done in parallel to the body structure. This again could be increased using topology optimisation.

Furthermore, the simple construction allowed easily repairing or adopting the car for other applications. Today’s trend towards multi-material design was also consequently utilised those days. Hence, a modern concept has to combine the success factors of the historic model with the dominant requirements of a car to be launched in 2015.

SCENARIO ANALYSIS With the aim to meet the major demands that a world car has to accommodate in the 21st century, a scenario analysis for the target year 2015 was carried out. Social, economic and technologic trend studies, for example [1, 2], have been regarded and were amended by own findings.

The major influencing factors are given by the mobility demand, legal regulations, the availability of energy and the market situations. The focus was placed on the markets of the Triad as well as of emerging and developing countries.

THE SUCCESS FACTORS OF THE HISTORIC MODEL T

The need for mobility is increasing worldwide.

Individual mobility will stay the basic need of mankind. With alternative means of transport being able to fulfil these needs only to a limited amount, the vehicle market will grow especially in the emerging countries. Besides the trend to mega cities, the majority of the population will still live in rural areas. Regional differences in availability and development of transport systems, infrastructure and routes have to be regarded for the target scenario. The new Ford Model T as a world car has to meet not only the requirements and customer demands of accessed markets but also increase the brand awareness and attractiveness in export markets to be accessed.

In parallel to individual mobility, customers also ask for automobile individuality. Open source approaches with defined interfaces can be adapted to vehicles and offer one potential solution for conflicts in relation with the individualisation of a mass product.

Only five years after the foundation of Ford Motor Company in 1903, the production of the Model T started. Its success was gained by fulfilling the market demands of those days to a very high level. Besides a classic passenger car, it was also used as a truck, tractor or even tank. In addition, the main success factors were the low sales price of 650 US dollar and its robustness for the poor and unsurfaced roads of the era.

Furthermore, the age structure of clients is of importance. The age pyramid is showing an aging population. This aspect is to be met by the concept amongst others by optimised ergonomics offering a high and up-right seat position. One central feature of the scenario analysis was the question which energy sources are available and accordingly which drivetrain options are best-suiting for the year 2015. The results show

Figure 2. Flow chart of the concept development

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that the internal combustion engine will keep its dominant role besides all on-going efforts towards hybrid and electric vehicles, Figure 3.

Main factors are the energy infrastructure as well as lasting high costs for electric energy storages.

Alternative propulsion concepts will gain importance in some markets though due to legal requirements (city limitations and CO2 taxation) as well as demands by customers with ecological awareness.

Figure 3. Distribution of propulsion systems and markets in 2015

MODEL T CONCEPT FOR 2015 The low sales price was a key challenge during the development of the concept. Different studies have shown that low-cost cars can be offered profitably at a sales price of 7,000 $ or even below [3, 8, 9, 10, 11]. Consistently, changes in production, sales and distribution but also design are claimed to be necessary in order to succeed.

This includes low-investment for on-site assembly of smaller volumes in lean production with increased manual processes. Standardised lowcost components, which are used by different brands and produced in low- cost countries, socalled “industry modules”, enhance the economy of scale. The global vehicle structure has to be designed for basic functionality with low complexity of parts. A modular design of the vehicle enables further economy of scale and reuse of particular parts. At the same time, this carry-over reduces R&D costs that can be further optimised by extensive implementation of simulation tools.

For automotive low-cost strategies, the part of logistics and sales is important. A reduced centralised dealer network is essential. Even sale via internet is an option. Finally, marge and costs for marketing have to be reduced.

The aspects motioned above were considered in the early concept phase when setting the target costs for the Model T. The subsequent concept development was attended by target costing.

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Therefore, target costs for the main components body, chassis, interior and electronics had to be established first, Table 1.

Accordingly, the maximum allowable cost of each component had to be established, assuring not to exceed the basic sales price of 7,000 $.

The percental distribution is based on a typical cclass vehicle (class of compact vehicles) [3]. The different cost items were derived from this percental distribution while the concept specification was determined from the scenario analysis, following market economy principles, as well as the major success factors of the historic Model T and the cost target.

Therefore, the main dimensions were defined at first, influencing not only the outer appearance but also some essential technical properties.

The trend towards smaller cars is apparent. One reason among others is the fact that the average number of passengers per ride is as low as 1.4 [4]. Accordingly, the team agreed very early that a modern Model T shall be positioned in the C-class. At the same time, there is an increasing demand for interior space and luggage by the emerging markets in which the new Model T shall be the first vehicle. The compromise of compact appearance and offered space was finally found in a short but wide vehicle with relatively high ground clearance and an up-right seat position for the passengers, Figure 4.

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Table 1. Target cost definition in US dollar

Basis sales price 7000 $ Production costs 4970 $ Assembly 890 $ Body 980 $ Chassis 800 $ Drivetrain 880 $ Interior Electronics

750 $ 630 $

Additional costs 2030 $ Logistic Marketing Overhead Guarantee

420 $ 560 $ 420 $ 250 $

Marge

420 $

Figure 4. Technical specifications of the new Model T

The width of the car allows sufficient space for three passengers in one row. The driver is centrally positioned and slightly ahead of the two passengers. This avoids different models for left and right hand steering. The concept is characterised by modularity, scalability and individuality, going from derivates, Figure 5, that are based on the scalable basic structure via changeable outer plastic panels to the drivetrain concept.

Package, vehicle architecture as well as structure of the modern Model T are easily adoptable for

Figure 5. Styling of the derivate vehicles

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usage as a hybrid drive, a plug-in hybrid drive or pure electric drive. The base model is driven by a gasoline engine as internal combustion engine (ICE). Its position in the rear of the car, together with the semi-trailing arm axle, is supporting an efficient package, can easily be accessed and thus allows the modularisation of the drivetrain.

In the front section there is a high freedom of package. This offers space for a maximum of passive safety.

Besides technical concept specifications, styling requirements for the new Model T had to be defined. A complete retro-styling approach as often used for remakes of automotive icons did not seem feasible from a technological, economic and design zeitgeist point of view for the 100 years old Model T. The idea was rather to transfer distinctive elements of the historic styling such as the massive cooler frame or the characteristic wheel house arc and to combine them with current styling characteristics. A worldwide commonly used design concept is believed to foster the brand identity, an aspect that is gainResearch and design in commerce & industry 8(2010)4, 186

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ing importance for success in the market due to an increasing technical unification. Following the definition of the concept specifications, the development of the different main vehicle components started in parallel. Body and drivetrain development are described in detail in the following chapters. At the end of the project, a cost assessment of the complete concept was carried out. Table 2 shows the overview of the total costs for the different drivetrain options of the variant compact pickup model.

The efforts for cost models increase more than proportional with the degree of detail respectively accuracy. Hence, an efficient cost prognosis must be based on analogies. Starting with comparable components with known cost structures, the costs of the new Model T components have been scaled using values such as dimensions, weight, power, energy content etc. [3, 5, 6]. While current market prices have been used for standard components, the electric drivetrain

had to be calculated using price prognoses for future price development under mass production assumptions [7].

Besides the economic and production-wise cost reduction strategies mentioned above further conceptual cost reduction methods enabled the low basic sales price. In addition to the avoidance of a left and right hand steering model, some comfort functions have not been implemented but are technically compensated to a certain extent. Furthermore, only standard tools are required for production, the passenger seats are not adjustable and planar glazing as well as module and common part strategies are used, altogether having a positive cost effect. According to the historic Model T, long production duration is planned. The changeable outer panels, the lighting parts and the interior allow an easy re-design and technology updates, thus keeping the Model T modern and appealing over a long time.

Table 2. Cost overview in US dollar of the variant compact pickup model for different drivetrain options

ICE Production costs Assembly Body Chassis Drivetrain Interior Electronics Additional costs Logistic Marketing Overhead Guarantee Marge Total

4930 $

Hybrid drive Plug-in hybrid drive 15 km 56 km 5340 $ 6890 $ 8190 $

electric drive 75 km 140 km 7410 $ 11,790 $

890 $ 960 $ 742 $ 780 $ 750 $ 588 $ 2070 $

890 $ 960 $ 742 $ 1280 $ 750 $ 718 $ 2100 $

890 $ 960 $ 742 $ 2830 $ 750 $ 718 $ 2160 $

890 $ 960 $ 742 $ 4130 $ 750 $ 718 $ 2210 $

890 $ 960 $ 742 $ 3350 $ 750 $ 718 $ 2180 $

890 $ 960 $ 742 $ 7730 $ 750 $ 718 $ 2360 $

420 $ 560 $ 420 $ 250 $ 420 $ 6780 $

420 $ 560 $ 420 $ 280 $ 420 $ 7440 $

420 $ 560 $ 420 $ 340 $ 420 $ 9050 $

420 $ 560 $ 420 $ 390 $ 420 $ 10,400 $

420 $ 560 $ 420 $ 360 $ 420 $ 9590 $

420 $ 560 $ 420 $ 540 $ 420 $ 14,150 $

BODY For the body development the trade-off between low-cost and lightweight had to be put in focus, since both requirements were formal objectives of the challenge. The team added the additional target to design a body type compromising the Research and design in commerce & industry 8(2010)4,186

special demands of conventional and electrified drivetrains in a common platform. This is to enhance the market relevance of alternative drivetrains by cost reduction due to economies of scale. In addition, to enable various derivates the body should be designed scalable in length and should be made of simple parts manufac-

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tured using standard tools.

Comparing different types of body design showed that these requirements in total can be met best using a hybrid design of steel deepdrawing parts and profiles together with plastic outer panels. On the one hand the team applied structural lightweight design techniques for the cost efficient steel basic structure. On the other hand for the body panels the lightweight potential of the material was used. The principle of structural lightweight design is to select the topology of the structure based on the loads acting on it.

This means material shall be applied at the actual load paths only. In order to determine these load paths, the team used the method of FEMbased topology optimisation. The staring point for this was the available design space for the body. This describes the volume that remains when subtracting the wheel envelopes, the interior space and all package components from the volume enclosed by the outer contours of the vehicle. The design space was meshed and the load cases such as static torsion and bending as well as quasi-static dummy loads for front, side and rear crash were applied. After calculating and masking the finite elements that are less relevant for the load cases in terms of stiffness, the abstract load paths could be analysed. This topology had to be interpreted and transferred to producible and joinable parts using CAD tools, Figure 6.

part is characterised by a stretched shape. In addition, all parts in the area close to the rear crossmember are parallel and exactly straightline. This way, the body can be scaled in length at this area as well as at the front and rear overhangs, Figure 7. For the doors and lids that show a profile-intensive design, the hinges are integrated in the support structure.

Figure 7. Vehicle components

DRIVETRAIN The background for the drivetrain concept was defined by the results of the scenario analysis.

The demands of future drivetrain systems with regard to efficiency and emissions will become stronger due to rising energy prices and stricter legal requirements. Considering these, potential drivetrain concepts for the modern Model T were analysed and compared regarding re-powering infrastructure, qualification for vehicle integration, total efficiency and production costs, Table 3.

In addition to conventional drivetrains based on combustion engines, unconventional systems were taken into account. However, the comparison of the different systems revealed that for 2015 the internal combustion engine will still offer the best compromise. Reduced fuel consumption can be achieved by combining efficient, downsized engines with lightweight compact-class vehicles.

Figure 6. Topology optimisation and CAD design

Following the results of the topology optimisation the CAD model includes a main longitudinal member that merges the sill, a very stiff rear crossmember designed as an integral part with the passenger backrest, a sandwich floor structure and two longitudinal floor members. Each

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However, electrified drivetrains should not be neglected in order to serve the growing demand for these vehicles in the Triad markets. Consequently, the modern Model T offers different drivetrain options on the same platform. The systems are going from the conventional gasoline drivetrain via hybrid and plug-in hybrid to the battery electric vehicle. Both battery electric veResearch and design in commerce & industry 8(2010)4, 186

Lutz Eckstein and etc. - “A car for everyone� - The winning concept of the international ford model T challenge

Table 3. Qualification matrix for drivetrain systems

Compressed air Gasoline engine Diesel engine Electronic hybrid Hydrostatic hybrid Fuel cell Battery electric drive Hydrogen ICE Natural gas ICE

Re-powering infrastructure

Qualification for vehicle integration

Total energy efficiency

Production costs

++ + 0 0 -0

-++ ++ + --0

-0 0 ++ ++ + ++

++ ++ + 0 ----

-

0 +

0 0

0 0

hicle and plug-in hybrid are able to run fully in electric mode. A modular drivetrain construction kit was developed for this in order to maximise the number of common components, Figure 8.

Since the daily range has significant influence on the operating costs for the plug-in hybrid drive option, the emissions and the efficiency of the vehicle, the battery system is designed in a modular way. This means, the customer can select the energy content of the battery based on his personal demands, for example the distance from home to office. In the next step, the components of the different drivetrain options were dimensioned and selected considering the outer vehicle dimensions, the vehicle mass, the top speed, an assumed aerodynamic drag coef-

ficient of 0.3 and different driving cycles.

For dimensioning and further evaluation of power requirement and energy consumption, a model library for simulation of longitudinal dynamics in Matlab/Simulink was used. Depending on the particular driving cycle and the drivetrain system, a peak power requirement from 17 to 28 kW was determined. Consequently, a 30 kW ICE or a 40 kW hybrid drive were selected. With the level of drivetrain electrification, the costs increase, Table 3. However, operating costs and emissions can be reduced. For instance CO2 emissions vary between 54 g/km and 100 g/km for the different drives while a specific CO2 emission of 500 g/kWh for electric power generation is assumed.

Figure 8. Drivetrain construction kit Research and design in commerce & industry 8(2010)4,186

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SUMMARY Only three months were needed by a team of the Institut für Kraftfahrzeuge (IKA) of RWTH Aachen University in order to develop an innovative vehicle concept which is capable of carrying conventional as well as alternative drivetrain modules thanks to its scalable design – a modern “Tin Lizzy” for the year 2015 with a basic sales price of less than 7000 US dollar.

An efficient approach and an effective realisation of requirements allowed the concept to be simple, light and compelling – following the spirit of its predecessor. A focus was therefore placed on a simple production and a robust design of chassis and body as well as possibilities for an individual styling by using changeable outer panels. The modular drivetrain allows to offer alternatives to the at least in the medium-term still dominant internal combustion engine such as hybrid or battery-electric traction.

The IKA made it possible to develop a completely new vehicle concept which fulfils all given requirements. These were depicted both from the challenge by the Ford Motor Company as well as a detailed analysis of the aimed markets in 2015. The biggest challenge was given by the basic sales price which was not to be exceeded. In the end, real costs were estimated to be slightly below with only 6780 US dollar. A new interpretation of historic constructions based on modern technologies allows interesting solutions for low cost vehicles in very short time. Finally, the team of ika thanks the Ford Motor Company for being part of the Challenge 2008 which was inspiring and fostered the creativity of students as well as researchers. It was an outstanding example which both stimulated and supported the personal advancement of young academics.

REFERENCES 1) Stigson, B.; et al.: Mobility 2030 – Meeting the Challenges to Sustainability. World Business Council for Sustainable Development, 2004 2) Sticher, G.; et al.: Das nachhaltige Automobilunternehmen – oder das Comeback des Elektroautos. In: 17. Aachener Kolloquium Fahrzeug- und Motorentechnik, 2008, Aachen 3) Kellershof, E.; et al.: Das 5000 € Auto: Ero-

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berung eines neuen Fahrzeug- und Kundensegments. In: 14. Aachener Kolloquium Fahrzeug- und Motorentechnik, 2005, Aachen 4) Halbritter, G.; et al. Optionen zur Entlastung des Verkehrsnetzes und zur Verlagerung von Straßenverkehr auf umweltfreundlichere Verkehrsträger – Ziele und Methoden eines TAB-Projektes. In: Bechmann, G. (Hrsg.): Praxisfelder der Technikfolgenforschung: Konzepte, Methoden, Optionen. Frankfurt u. a.: Campus 1996, p. 267–295 5) Osburg, B.; et al.: NSB® NewSteelBody: Technische Dokumentation. ThyssenKrupp Printmedia GmbH, Duisburg, 2003 6) Osburg, B.; Patberg, L.; Grüneklee, A.; Flöth, Th.; Große-Gehling, M.; Hinz, M.; Mebus, H.: New Steel Body – Sicherer und wirtschaftlicher Karosserieleichtbau mit Stahl. In: ATZ Automobiltechnische Zeitschrift 106 (2004), no. 3, p. 190–199 7) Vergels, F.: Sustainable Batteries – Assessment of Environmental Technologies for Support of Policy Decision. Electric Vehicle Symposium 21, Monaco, 2005 8) Bernhart, W.; et al.: Low-Cost Car Creation - High-performance business models for low-cost vehicles. In: automotive inSIGHTS (2008) no. 1, p. 6-9 9) Mayer, S.; et al.: Mega-Markt für Ultra-LowCost – In Schwellenländern wächst die Nachfrage nach Niedrigstpreis-Autos. A.T. Kearny Study, Düsseldorf, 2007 10) Van Acker, W.; et al.: The early bird catches the worm – Low cost car market segment.

Roland Berger Study, 2006 11) Meiners, J.: Low-Cost-Cars. In: Automobil Industrie (2007), no. 6, p. 26-35 Paper sent to revision: 21.10.2010.

Paper ready for publication: 02.12.2010.

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Paper number: 8(2010)3,187, 205 - 214

A POSSIBLE ANSWER TO THE QUESTION: WHAT IS ASSET MANAGEMENT? Dr Vladimir Popović* Faculty of mechanical engineering, Belgrade Prof. dr Branko Vasić Faculty of mechanical engineering, Belgrade Dr Dejan Curović Faculty of mechanical engineering, Belgrade Asset Management is the culmination of a long history of development in the management of physical assets. It is about asset intensive businesses achieving a level of service, risk profile and funding requirement that is acceptable to stakeholders for the life of the assets. Asset Management involves making decisions about the interventions to physical assets required to achieve this, and can often involve a trade-off between short-term and long-term benefits. Good Asset Management concerns itself with the justification of decisions based on the best use of available information and the most appropriate tools and techniques for deciding what the optimum trade¬offs are between the costs and risks inherent in all asset lifecycle activities. Ensuring organizations implement good Asset Management is of increasing interest and importance not only to the organizations themselves who stand to save vast sums of money and to control risks more effectively, but also to regulators and customers who seek best value for money and consistently good output performance both now and for future generations. Understanding, measuring and improving Asset Management capability is therefore of increasing interest too.

Key Words: Asset Management; Maintenance MAINTENANCE AND ASSET MANAGEMENT The design of maintenance system and the corresponding logistic support is a very complex process, during which the aim is to find the compromise solutions regarding the relations among different maintenance procedures and the ways of their implementation. As a result of this, various solutions can be adopted, since this is conditioned by a series of of important factors and criteria, which can be contradictory sometimes [7]. There are different perspectives on ways of solving practical maintenance problems, that is dilemmas when it comes to the choice of maintenance concept. The principal dilemma is how and when to decide on carrying out maintenance procedures. Should the decision be based on theoretical grounds or experience, how does one reconcile those two extremes, who is to decide upon this?

The importance of prevention of failures in indus-

trial facilities, and their timely identification and correction, if they occur, cannot be overstated.

An indication of the amount of attention various aspects of maintenance have attracted in recent years, is the number of publications and books published. Generally speaking, from a broad theoretical and practical aspect, maintenance is defined as the combination of all technical, administrative and managerial actions during the life cycle of an item intended to retain it in, or restore it to, a state in which it can perform the required function [4]. Thus observed, maintenance is a complex functional system, united by a single goal and unique criterion function. In engineering sense, the system of maintenance of one machine, device or any other technical system can be realized in various ways and variants.

Quite often the term “maintenance” has a negative conotation. In most organizations, the func-

Faculty of mechanical engineering, Kraljice Marije 16, Belgrade; vpopovic@mas.bg.ac.rs

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tion of maintenance system is regarded as the lesser evil or a needless cost, the so-called “white elephant”. Due to this conotation, insufficient time and effort is spent on activities of maintenance control and the resulting cost. It is a well known fact that, during the analysis of lifecycle cost of a technical system, the most visible is usually the most evident, and that is acquisition cost. However, the “invisible” part that represents operational cost, maintenance cost, spare parts and supply cost, staff training cost, the cost of provision documentation on handling and maintenance etc., significantly exceeds the acquisition cost. For that reason, there are constant efforts to identify and treat in a much better way this bigger portion of cost. It is evident, for the above-mentioned, and many other reasons, that there is a need for developing new methodological approaches to maintenance concept selection, and looking for the ways to improve the existing methods [5-7].

Organisations worldwide are looking for opportunities to reduce the cost of maintaining their assets, improve the performance of those assets through effective decision making, and gain competitive advantage. In many industries regulatory requirements as well as safety criticality of these assets add to the complexity. In this environment, it is essential for organizations to accurately track the current configuration and trace historical configuration changes throughout the asset lifecycle. However, traditional configuration management systems have often proved inefficient for managing maintenance, repair and overhaul data because they represent only the last asset configuration and fail to provide the ability to consistently trace the current and historical changes to the asset configurations.

Hence organizations often experience a lack of information between the initial acquisition of the asset and the following service operations. For instance, the acquisition information regarding the asset is often obsolete due to changes in the asset setup since installation, and considerable amounts of time are wasted on inefficient updates. For all of the above mentioned, the importance of the new and broad approach to maintenance of all systems – the concept of Asset Management, is quite clear.

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INTRODUCTION Asset Management emphasizes integrated approach in decision making. It integrates asset development, operating of asset and upkeep of assets. An important part of asset development is determination of capacity needs and capacity creation which means investment planning and investments. Operating of assets means production and especially the part of production that influences assets and their prevailing production capability. The last dimension, upkeep stands for the maintenance function. Although business oriented Asset Management sounds at first glance working against sustainable production methods, it actually supports sustainable development strongly, because Asset Management strives at economic use of scarce resources taking into account market dynamics.

We need Asset Management, e.g. to manage our investments and capacity in the more competitive way. There are many reasons for losses during the life cycle of production equipment, which demand for the more effective Asset Management [3]: • • •

• • • •

•

economic lifetime is not in balance with technical lifetime, all processes are not functioning at the same operating rate, during process and product transitions production capacity of large concentration of assets is lost, demand does not match with capacity, during installation and commencing of investments production losses may be huge, low OEE (overall equipment effectiveness) causes production losses, due to low flexibility of assets equipment is used in ineffective way (product mix and insufficient adaptation to demand fluctuations), construction of equipment is not up to date.

In order to minimize the above mentioned production losses during the life cycle of the equipment, replacement investments and maintenance activities has to be optimized. Typical Asset Management decisions and questions linked to replacement investments and maintenance activities within plants in operation are following [3]: Research and design in commerce & industry 8(2010)4, 187

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• • • • •

•

should we replace or maintain, should we modernise or replace with the similar one, where should we replace when should we replace, what would be our budget, which level technical performance should be aimed at what availability performance should aimed at, what OEE would be optimal.

Plants’ internal strategic traits (role in corporate production system, competitive position, product portfolio and economic structure), development in the markets and available technology and its development determine critical success factors for the engineering assets. The used technology gives limits and potential to the plant’s ability to meet the requirements of the markets.

Asset Management definitions

•

•

•

There are many definitions of Asset Management. If we use Google to get the answer to the question from the title of this paper, we get the following responses: •

•

•

•

•

Investment management is the professional management of various securities (shares, bonds and other securities) and assets (e.g., real estate), to meet specified investment goals for the benefit of the investors. Investors may be institutions (insurance companies, pension funds, corporations etc. (en. wikipedia.org/wiki/Asset_management) Fixed Assets Management is an accounting process that seeks to track fixed assets for the purposes of financial accounting, preventive maintenance, and theft deterrence. (en. wikipedia.org/wiki/Asset_management_general) A process that oversees the cradle-to-grave status of key plant-floor machinery. It involves the acquisition of such equipment, along with their use, function and ultimate disposal, in order to maximize their potential performance and longevity. (www.reliableplant.com /Glossary) A management system that ensures the efficient use of business equipment such as vessels, measuring equipment, etc. (www. fugro.com/corporate/faq.asp) The practice of taking a comprehensive view

Research and design in commerce & industry 8(2010)4,187

•

•

of the entire portfolio of resources available in order to achieve system-wide agency goals at optimal cost benefit. This includes the ability to show how, when, and why resources were committed. (ops.fhwa.dot.gov/publications /fhwahop09028/glossary.htm) The investment of large sums of money, normally in stocks and shares or other interest bearing accounts for the purpose of either producing an income or growing the original capital sum or a mixture of both. (www.cwseriousinjury.com/glossary) Range of services offered by banks for the active management of a client’s assets under a portfolio management mandate. Asset Management is essentially synonymous with portfolio management or wealth management but in practice often refers to the service provided to institutional investors. (www. ubs.com/1/e/gcc/bankingterms.html) Professional services and activities aimed at maximising the value and return of the fund’s real estate assets, by identifying measures enabling strategic Asset Management.(eng. fondoalpha.it/_sef/Glossario.php) The management of a portfolio of assets (e.g. bonds, shares, cash, property) of an individual or company in order to maximise return on investment. This is a service provided by financial advisors such as Acumen & Trust. (www.acumenandtrust.com/glossary/) The various disciplines involved with managing real property assets from the time of investment through the time of disposition. (www.searchsacramentohomesforsale.com /real_estate_glossary.html)

It is quite clear that none of the previously given definitions provides an absolutely accurate answer to the question: What is Asset Management?, but each of them offers one of the possible answers to this question from a certain angle.

An important issue arises – is it possible, due to the breadth and the complexity of the concept of Asset Management, to define it in a simple way, and in one sentence.

WHAT IS ASSET MANAGEMENT? Simply put, Asset Management is “The optimal life cycle management of physical assets to sustainably achieve the stated business objectives” [8]. Asset Management allows asset intensive

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businesses to use limited resources to achieve their stated business objectives in the most cost effective way. It combines engineering and mathematical analyses with sound business practice and economic theory. This definition leads to some key principles which any Asset Steward should follow [8]: • • •

Decisions shall be clearly linked to the overall business objectives; Asset Stewards shall manage risks and not resources; Decisions shall be analysed for whole systems and not their parts;

• • • •

Decisions shall be made from a whole-life perspective; Asset Stewards shall leave assets in at least the same state they inherited them; Uncertainty shall be actively embraced and managed; and Stakeholders shall have a full understanding of the choices available.

Asset Stewards can begin to deliver Asset Management in line with these principles by focusing their organizations on the management of the asset lifecycle, as shown in Figure 1 [8].

Figure 1. Making Asset Management the focus of an organization’s activities

CONCEPT OF ASSET MANAGEMENT Asset development contains e.g. determination of business needs: • • • • • •

expected life cycle, capacity, capability, flexibility (in relation to volume and /or product), efficiency, performance rate (e.g. operating rate, OEE, maintenance costs).

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Asset development contains also determination of asset options to be used, design and construction of production equipment in compliance with life-cycle needs, capacity, capability, flexibility, efficiency and performance rate requirements (maintainability and reliability included). Operating of asset may have significant effect on production assets e.g. [3]: • • •

allocation of orders on various plants or production lines, break downs because of misuse of assets, OEE oriented activities, Research and design in commerce & industry 8(2010)4, 187

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•

•

immediate production actions such as process control and machine operations, operation can also include adjustments or replacements of consumables, etc., in addition to operation, operators’ duties include tasks related to integrated operation and maintenance such as sanitation, cleaning, lubrication, settings, minor repairs of production machinery as well as machinespecific condition monitoring and follow-up of production capability.

The system of the maintenance function consists of several separate sub-processes [3]: •

determination of requirements,

•

determination of maintenance objectives,

•

maintenance planning,

•

resources management and development,

•

management of maintenance processes,

•

execution,

•

follow-up and continuous improvement

All these three dimensions influence each other and should be therefore handled in an integrated way as illustrated in Figure 2 [2].

All the above mentioned dimensions interact with each other. For example, operating and mainte-

Figure 2. EFNMS conceptual model of Asset Management

nance of assets has a significant influence on asset development. Exogenous influencing factors such as market development, technological development, financing of assets and stakeholder requirements affect asset management activities (planning, decisions and implementation). Actually, market and technology development are key factors when determining the critical success factors of the business in question and requirements on assets. Financing and stakeholders give constraints to asset management activities.

Legislation and EU requirements give a societal framework for Asset Management [3].

Figure 3. Two guiding factors of Asset Management [2] Research and design in commerce & industry 8(2010)4, 187

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There are at least two standpoints when creating investment policies and carrying out investment oriented Asset Management. The one is reactions to the changes in the business and technological environment and the other is to make investment decision based on life-cycle profit (LCP) or life-cycle cost (LCC) calculations. Especially in the case of replacement and development investments to the old production line, LCP or LCC-approach would often be a powerful tool to make effective decisions.

A LCC/LCP analysis can be applied to the evaluation and optimization of the life cycle costs and profits of the investments taking into account specified performance, safety, reliability, maintainability and environmental requirements. Other reasons for performing LCP-analyses can be, for example, to identify cost effective improvements and cost drivers (i.e. cost factors that have large-scale impacts on the investment profitability), or to choose between different suppliers and products. However, as soon as the installation of the equipment has been carried out the business environment begins to change (Figure 3).

Changes may occur in all the exogenous or internal factors which the investment calculations have been based on [3]. The essential question is how to sustain or improve the life cycle profits of the original investment. Another essential question is how to ascertain high life cycle profits for green field investments or the replacements of the whole production line. These ones are the core issue of Asset Management of the production assets. In the case of replacement or development investments to the old operating plant or production line LCP or LCC-approaches combined with some other economic indicators could give the better indication of the profitability of investments than many of the traditionally used indicators.

WHY IS ASSET MANAGEMENT IMPORTANT? The world is facing a growing challenge with respect to the ability of global society and indeed the planet itself to meet the needs of an increasingly growing and demanding population. Infrastructure investment in the emerging economies will be $2.25 trillion annually over next three years [11], and in the US the ASCE reports that US infrastructure requires investment of $2.2 trillion over the next five years, twice the expenditure

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currently planned [10]. In Britain a recent study by the Policy Exchange concluded that investment in Britain’s infrastructure, which is among the oldest in the world, needs to be £434bn by 2020 and that the 18% productivity gap between Britain’s and France’s productivity is in large part due to Britain’s ageing infrastructure [9].

Add to these raw figures the growing concerns over the social and environmental impact of infrastructure projects, questions are bound to be asked about what we will hand over to future generations. Forum for the Future, a UK based sustainable development organization, recently published its thoughts in ‘Rethinking Capital’ [12]. It concluded that falls in capital markets, most notably during the recent economic crisis, occur for a number of interlinked reasons [8]: • • • • •

Incentives are not aligned with the public good; Critical goods and services are not valued or are under valued; We lack imagination and awareness about new and systematic risks; Regulation is inadequate; and Progress is based on unsustainable growth models fuelled by credit.

Although Asset Management cannot answer these questions directly, it can provide a longterm view, based on rational and justified analysis, of the impact of decision-making on complex infrastructure portfolios which can strongly support the right decisions. The key decisions are [8]: • • • • • •

How, where and in what to invest?

What risks need to be managed?

How to trade-off short and long-term costs and risks?

What demands must be served?

Where can costs be deferred or cut?

Can this be done without cuts in service levels?

All of these decisions of course, have to be made in the face of huge uncertainty. We must therefore not be put off making hard decisions because they are uncertain. The processes that underpin good Asset Management can us help understand and reduce this uncertainty, and so give us a better route to success.

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THE ASSET MANAGEMENT SYSTEM The Institute of Asset Management, the UK member of the EFNMS, defines the asset management system as [1]: Systematic and coordinated activities and practices through which an organisation optimally and sustainably manages its assets and asset systems, their associated performance, risks and expenditures over their lifecycles for the purpose of achieving its organisational strategic plan.

However in a sense there is nothing special or new about asset management systems. A number of elements of modem asset management systems have been used for many years. For example the manufacturing sector has developed a range of operating and maintenance regimes which maximise the productivity of its factory assets. Furthermore Asset Management is not an exclusive activity. Almost everyone in an asset intensive business has some role to play in the asset management system. On a day to day basis operational staff will be maintaining and running existing equipment assets while in the board room new investment plans which may add capacity, or increase production flexibility or efficiency are under consideration. Accordingly it may seem strange that Asset Management has, over the last 20 years, become a subject in itself. However there are three factors which are changing the business environment of asset rich organisations, and creating a need for more effective Asset Management. These three issues are [1]: 1. Short and long term conflict: Operational staff often see the need for day to day maintenance most clearly, while senior managers are looking even harder for ways to reduce investment. Getting the balance right between these two conflicting pressures is becoming more difficult.

2. Complexity: Complex businesses create complex conflicts and make it difficult to allocate investment efficiently. How often have we seen someone get funding for the wrong reasons?

3. Oversight: These days there are many people prepared to examine our decisions looking for errors in our work. For example after an accident our every decision can expect to be studied and questioned. We have to be Research and design in commerce & industry 8(2010)4, 187

much better at demonstrating why we had to make the decisions we have made.

What is good asset management practice?

In order to be effective and efficient good Asset Management requires a clear and ‘joined up’ understanding of the most strategic and the most tactical business decisions being made. Figure 4 illustrates the different types of tasks which need to be undertaken.

Figure 4. Strategy hierarchy of asset management decision making [1]

For a ‘normal’ manufacturing business a small group of people may be able to take a view on Level 1 and Level 2 objectives. However form a complex business with many operational sites, of a regulated utility which if only funded for the ideal investment plan decision making can be much harder to get right. All utilities and many companies employ people who find others within their own business make decisions which make it difficult for them to do their job well. For a well organised business ownership of decision making for each of these different levels of thinking may well rest with different departments or groups of staff across the company. However by having ‘owners’ who are accountable for each of these levels of thinking and who are prepared to work constructively with others in the asset management system is critical. Ultimately the most strategic aspect of any decision needs to be sponsored collectively by the board of the company. In this way while particular departments of groups may ‘own’ certain types of decisions, the most senior leaders across the organisation need to be comfortable with the most strategic decisions being made which affect their accountabilities. Implemented well decisions are more likely to reflect all the important factors which add or destroy value in the organisation.

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It should be noted such systems need not be complex however there is a great tendency for them to become bureaucratic if allowed to do so.

This may be because almost any higher level document or objective has the scope to accumulate detail (much of it increasingly duplicated in other documents) and so create a source of potential confusion. If the important issues cannot be clear in several paragraphs there may be a deeper problem which needs clarity.

The need for capable asset management systems A review of asset management practice in a range of utility companies located across the world has indicated asset management approaches vary significantly across the world. As asset management systems add costs as well as gives visibility of risks and value. It is this complex trade-off which determines what sort of asset manage-

ment system is appropriate for a particular utility organisation. These conflicts are illustrated by the figure 5 [1].

The Climate, Complexity and Goals are the factors which determine the type of capability of the asset management system which is appropriate for a particular business. For example a utility which operates in a tough regulatory environment, and which must enter into fixed price five year regulatory contracts, has a greater need for a sophisticated asset management system than a utility whose budgets are reviewed annually in the light of events. However once an organisation has resolved to establish a certain type of system it is the Tools, Organisation, and Teams determine the actual capability which a particular business is able to achieve at any point in time.

Climate and Complexity are particularly defining factors.

Figure 5. Asset management capability model

HOW CAN ASSET MANAGEMENT BE MEASURED? The development of an organisation’s capability in Asset Management can be described in terms of developing maturity, i.e. from initial awareness of the importance of asset management processes (or ‘Innocence’), through to a state where the organisation’s asset management processes are appropriate, sufficient and capable of producing consistently good performance (or ‘Excellence’).

This is summarised in Figure 6 which shows the

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impact of asset management capability, or maturity, in the horizontal dimension and the performance / outputs of an organisation in the vertical dimension.

Customers and regulators typically concern themselves only with the vertical axis of this matrix - the output performance of the organisation; yet the ability of the organisation to consistently deliver economic and sustainable performance requires mature asset management capability in parallel.

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Figure 6. Asset management capability versus output performance [8]

An “Under Performing” organisation is likely to lack the underlying capability to significantly improve consistently poor output performance. A “Promising” organisation is also likely to have consistently poor performance, but has at least recognised the need to develop process maturity, noting that there can be a significant lag between improvements in asset management decision-making and this being reflected in the outputs of an organisation.

Organisations that have a wide variability in their performance (i.e. sometimes achieving the desired performance, but not being able to maintain it) will typically have a focus on outputs, but a low level of underlying asset management capability.

This is usually the result of transitory efforts to address the ‘latest problem’ but often not in the most sustainable and economic way to deliver the required outputs.

CONCLUSIONS Asset Management can be defined as managing infrastructure capital assets to minimize the total cost of owning and operating them, while Research and design in commerce & industry 8(2010)4, 187

delivering the service levels customer’s desire.

It can be effectively use to improve operational, environmental, and financial performance of any system that delivers a significant service. Asset management programs with long-range planning, life-cycle costing, proactive operations and maintenance, and capital replacement plans based on cost-benefit analyses can be the most efficient method of meeting the challenge of providing the best possible service under numerous real-world constraints (e.g. limited funds, capacity).

Optimisation of assets and more particularly of engineering assets is a key and challenging issue for modern industrial societies. Engineering Asset Management (EAM) is an emerging interdisciplinary field that combines technical issues of asset reliability, safety and performance with financial and managerial requirements. The emphasis of EAM is clearly on sustainable business outcomes, risk management and value. EAM is concerned with assets throughout the lifecycle.

Efficient EAM is realised with the efficient development of closed loop product lifecycle management technologies allowing for the efficient man-

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agement of all the business processes distributed along the product’s lifecycle phases. Middle of life and particularly maintenance is of particular interest and importance for EAM. Along that line predictive maintenance and maintenance for sustainability approaches, models, methods and tools need to be developed.

Integrated view on the development of companies’ engineering assets has become more important and even vital in the very dynamic business environment which we meet today. Development of technical assets, development in operating them and development of the maintenance of those assets cannot be carried out separately, because it leads to sub-optimization and ineffective solutions. Productivity of capital could be increased, which results in more sustainable production. Demands for higher turnover of capital, better return on assets and improved sustainability of asset solutions in the fast changing business environment have led very sophisticated decision making situations where a lack of effective and proper decision making tools is evident. However, various industrial sectors differ from each other as far as the requirements on assets are concerned. Therefore, industry specific requirements should be clearly kept in mind when making decisions concerning engineering assets. These trends and business development mean that decision making concerning technical assets demand good technical expertise just as before, but in addition to that, expertise in business analyses and strategies is as important as technical expertise. Economic analyses are increasingly important in Asset Management.

Market dynamics, technological options, life cycle cost and profit objectives and life cycle cost structure have a significant influence on the plant asset strategy and strategic choices. Within the asset management framework a challenge to meet is how to sustain or improve the life cycle profits of the original investment and at the same time to improve the sustainability of asset solutions.

REFERENCES

2) Komonen, K. (2009). Asset management in the industrial sector: Background and conceptual approach, Maintworld, 1, 16-19.

3) Komonen, K., Raikkonen, M., Kunttu, S., Heikkila, A., Ahonen, T. (2010). Investments, capacity and maintenance: ways to safely increase capital turnover, Proceedings of EuroMaintenance Conference – Verona, 53-56.

4) Marquez, A.C. (2007). The maintenance management framework – models and methods for complex systems maintenance, London: Springer-Verlag.

5) Popovic, V., Vasic, B., Curovic, D. (2008).

Failure Modes, Effects and Risks Analysis – FMERA, Journal of Institute for Research and Design in Commerce & Industry, 20, 3342. (in Serbian) 6) Popovic, V., Vasic, B., Petrovic, M. (2010).

The possibility for FMEA method improvement and its implementation into bus life cycle, Strojniski Vestnik – Journal of Mechanical Engineering, 56(2010)3, 179-185.

7) Popovic, V., Vasic, B., Stanojevic, N. (2010).

Options for the choice of maintenance concept using risk-decision factors, Proceedings of EuroMaintenance Conference – Verona, 93-97.

8) Sharp, A. (2010). Developing world class asset management capability, Proceedings of EuroMaintenance Conference – Verona, 5759.

9) http://www.forumforthefuture.org/projects/rethinking-capital 10) http://www.infrastructurereportcard.org/report-cards 11) http://www.invest.baml.com/ Error?aspxerrorpath=/ch/bytestream.aspx 12) http://www.policyexchange.org.uk/publications/publication.cgi?id=132 Paper sent to revision: 06.11.2010.

Paper ready for publication: 13.12.2010.

1) Deadman, C. (2010). Results of a global review of the capability model of modern asset management systems in the utility sector and an assessment of future development trends, Proceedings of EuroMaintenance Conference – Verona, 69-71.

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Paper number: 8(2010)3,188, 215 - 221

HIGHER LEVELS OF MODELING BASED ON INVENTOR SOFTWARE Mr Rade Vasiljević* IRC NIC A.D., Užice In this paper, the higher levels of modeling were analyzed, which are in machine design and analysis products one of the most complex and most demanding phase. At this phase, an engineer-designer spent a lot of time in a matching of parts and defining the required constraints. On the one aspect, shortening this time is not achieved by either using today powerful software tools, while, on the other aspect, further increases without the existence of explicit procedures. To optimize the needed time in modeling the higher level of incorporation procedure is proposed in the form of structural diagrams. A software solution Inventor was presented in a systematic way. Special emphasis was given to higher levels of modeling. Solving higher-level modeling, using Inventor, illustrated on a concrete example of assembly.

Key words: higher levels of modeling, Inventor, assembly, matching, constraint INTRODUCTION Mechanical design and analysis of products is unthinkable without the support of modern software solutions today, [6]. Computer support contributes to the efficiency and effectiveness of industrial production, [5]. This is the result of a growing number of increasingly powerful and specialized software packages such as Inventor, Ansys, SAP2000, Catia, Solid Works, Pro Engineer, ADAMS and others. The list of software solutions, which are increasingly dominant place occupied by solutions from CAD. Students of mechanical engineering and mechanical engineers-designers usually successfully master the use software tools to parts modeling, but the problems appear in the phase modeling of higher levels of incorporation or assembly. This fact is established and in paper [2].

In general, a technical system is consisted of n components, where n≥2. Modeling process for complex systems may consist of three logical phases: • •

modeling of parts, modeling of subassemblies and assemblies (integration of parts and standard machine elements into higher levels incorporation), and

″IRC NIC″ AD, Nikole Pašića 38b/IV, 31000 Užice; rvasiljevic@ptt.rs

•

modeling of main assemby (integration of parts, standard machine elements, subassemblies and assemblies into higher levels incorporation).

In the second and third phase of modeling complex systems are defined by the kinematic relations, and constraints in terms of: • • • • • •

alignment of area, alignment of edges, alignment of axis, alignment of working points, defining the desired motion between two components, and identifying the relationship between the transient path fixed component and the component that moves along the path.

Each part can be assigned the appropriate number of freedom degrees and thus the degree of displacement or deviation part of the adjacent parts. It is very important to correctly define the constraints in the phase of high-level modeling.

Number of constrations should be both, sufficient and minimal. The achievement of this requires, a model assembly or model of any of its parts can be used as a substitute for a physical prototype.

In the following subtitles of this paper will first

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be presented the theoretical basis of higher-level modeling in Inventor, and then the same ilustrded on the example of the assembly of performed solution of electromechanical two post lifts. Finally, on this basis will perform a appropriate number of recommendations and conclusions.

•

GENERAL CONSIDERATIONS INVENTOR

•

Today There are a large number of software solutions that offer powerful tools for modeling high-level application today. In paper [2], shown two contemporary software solutions, CATIA V5 and Solid Works. In this paper the problem of modeling the higher level of incorporation will be presented at high-end software solution Inventor, Autodesk company. Autodesk is the world’s leading manufacturer of CAD software, [1, 4].

Inventor software package is intended for the design and analysis products on the computer.

At the time of paper writing the Inventor has arrived version 2011, [1]. It enables automate the design, construction and calculation. Based on a system for modeling assemblies solids (3D) and technical documentation creating (2D).

The importance of Inventor, as well as other software solutions from CAD group, is contained in the creating of 3D geometry. Inventor is a hybrid modeler that combines solid bodies and surface.

In the structure of Inventor are two separate modules for creating 3D geometry:

•

•

• • •

• • •

cordance with industry standards (ISO, DIN, BS, ANSI, etc.)

Presentation - enables animations mounting subassemblies and assemblies creating, Inventor Studio - enables animation and photorealistic images creating, Library - contains a library of over one million standard machine elements by various industry standards (ISO, DIN, BS, ANSI, etc.)

Design Accelerator - enables a large number of mechanical calculations and contain mechanical manuals over one million standard machine elements, FEA - enables the calculation assembly according to the method of finite elements, Dynamic Simulation - enables the dynamic simulation of assembly or mechanism, Tooling Suite - enables working with plastic parts and automated design tools for molding plastic Pipe / Tube - enables parametric modeling of pipes, hoses and connections, Harness / Cable - enables parametric modeling of cables and wiring, and IDF - enables a IDF file inserting with information of printed circuit boards and printed circuit boards modeling.

Part Modeler - enables parametric modeling and editing of solid bodies and surfaces, and Assembly Modeler - enables the design of mechanical assemblies and creating of specification, expanded screening etc.

Inventor, based on the created 3D geometry of the parts, enables composition and analysis of products using its virtual prototype. Using the model thus obtained, can be analyzed the product before making his prototype. By using Inventor software package, engineers-designers can very quickly identify errors and omissions on the model before the phase of production and thus eliminate unnecessary investment.

In addition to these modules, which relate to the title of this paper, the structure of Inventor are the following modules:

TOOLS FOR HIGHER LEVELS IN MODELING INVENTOR

•

•

• • •

•

Sheet metal modul - enables the design of plates and automatic unfolding of surface, Weldment Assemblies - enables the welded assemblies creating, Frame Generator - enables parametric 3D modeling and editing of steel structures using standard profile, Drawing Layout - enables technical documentation creating, automatic dimensioning, drawing different note, the symbols in ac-

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Assembly is a group that consists of one or more components of the design, where components can consist of parts or subassemblies, [3]. Assembling elements into an assembly in Inventor software package is implemented under the same principles which is used at the montage of a physical prototype. This software package offers tools for matching an engineer-designer to provide support for its work with higher levels of modeling. Tools matching enables the positioning, fixing and limiting components in the assemResearch and design in commerce & industry 8(2010)4, 188

Rade Vasiljevic - Higher levels of modeling based on inventor software

bly, ie. define the interrelationships between the components in the assembly. It can also enable motion freedom.

The first step to getting assembly is appropriate components grounding. Mainly, a base component or components that can not be moved in relation to other components is landed. In the second step can be implemented matching through Place Constraint tool, figure 1.

Figure 1. Tools for matching in Inventor (Active card Assembly)

constraints of the transmission is the movement of the movable cylinder along a fixed path (for example, roller and a tooth). The aim of transmission constraints is to determine how mobile component should follow a certain path. Eventually, other types of constraints from the card Assembly apply (for example, attaching the roller and the top teeth).

Figure 2. Card Motion tools Place Constraint

Card Assembly, figure 1, is the most commonly used and it enables paired, angular, tangential and constraint insertion. Options from this card are Mate, Angle, Tangent and Insert. Using these options exercised constraint assembly.

These limits define the place or position of components and fixed components in space. After the assembly constraints, constraints of motion are executed.

Card Motion, figure 2, defines the desired motion between two components, using the specified scale and orientation. Options from this card are Rotation and Rotation-Translation. Constraints of motion are present to components that rotate and move together (gears, racks, belt drive, bearings and carriers, wheels and lift tracks etc.).

These constraints define way the motion of mobile components in relation to other mobile or fixed components (for example, defines whether the two gears moving in the same or opposite directions). Eventually, other types of constraints from the card Assembly apply (for example, attaching the tops of two gears).

Card Transitional, figure 3, enables us to identify the relationship between the transient path fixed component and the component that moves along the path. A simple example to illustrate the Research and design in commerce & industry 8(2010)4, 188

Figure 3. Card Transitional tools - Place Constraint

During the modeling of higher levels of incorporation, it is important to analyze the constraints and errors. Number of components in the Browser tree Inventor is conditional and depends of the function of the assembly. On the one hand, each components in match defines the appropriate constraints, while on the other hand, the components were losing some of their freedom of movement. Number of constraints of one component should not be higher than the minimum and necessary. Any redundant constraint can cause problems in the process of analysis of products (simulation analysis, static analysis, dynamic analysis, etc.) Overextended constraints are

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marked and can be seen in the Browser tree Inventor. For the analysis of constraints the Drive Constraint option is available in Inventor, which, among other things, can detect collisions. Components involved in the crash are identified and will be displayed on the detection of a collision.

PROPOSAL PROCEDURES FOR HIGHER LEVELS IN MODELLING To have students of mechanical engineering and mechanical engineers-designers in addition to the successful mastering of software tools for parts modeling, successfully mastered and software tools for higher levels of modeling and assembly modeling is necessary to define problems in the modeling of higher-level incorporation.

Problems in modeling of the higher level of incorporation occur for the following reasons: •

•

•

•

insufficient knowledge of the function of parts and subassemblies into assemblies or subassemblies and assemblies in the main assemblies, needed knowledge and skills for successful modeling of higher levels of incorporation are not always at the appropriate level, examples of modeling high-level of incorporation in the instructions and literature are simple, as is the case in the papers [2] and [3], and operating procedures for the successful modeling of higher levels of incorporation are not explicitly defined in the instructions and literature.

One of the possible solutions of mentioned problems, the general procedure a modeling higher level of incorporation in the form of structural diagrams is proposed, figure 4.

In order to avoid design errors that may arise during the modeling high-level of incorporation, it necessary to constantly take preventive measures and carry out necessary activities according to the most logical order.

Verification of the validity of the proposed procedures for modeling the higher level of incorporation can best be shown on a concrete example of the product, so that it will be done on a concrete example of assembly in the following subtitle.

In this sense it is necessary to correctly set up the experiment of modeling the higher level of

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Figure 4. Structural diagram modeling higher levels Research and design in commerce & industry 8(2010)4, 188

Rade Vasiljevic - Higher levels of modeling based on inventor software

incorporation of selected example of the assembly. For the implementation of the experiment Inventor specialized software package is planned in this work, which is discussed in the preceding subtitles.

EXAMPLE HIGHER LEVEL MODELING Verification of the validity of the proposed procedures for modeling the higher level of incorporation into the Inventor software, is demonstrated for electromechanical two post lifts. To illustrate this example, the materials and results from the paper are used /6/. The experiment used a software package Autodesk Inventor Series 10.

The second step, the first fixed component is selected and imported into the Assembly Modeler, and then imported the free components into Assembly Modeler. For a fixed component is selected threaded screw, while the imported components as a free mobile carrier console.

Figures 5 and 6 shows the models of threaded screw (part) and mobile carrier console (subassembly) which form one of the possible variants of the decomposition of assemblies threaded pair electromechanical two post lifts.

In the first part of the experiment, according to the proposed procedure modeling the higher levels, activities prior modeling electro-mechanical two post lifts were first carried out.

In the first activity, the author of this work was made the analysis of performed the solution of electromechanical two post lifts manufacturer “Universal” from Banja Luka, the type of DB2: •

•

principles of operation of electro-mechanical two post lifts or higher levels of incorporation, and the place and function of each element in the electromechanical two post lifts.

Figure 5. Threaded screw - part

In second activity, based on previous activity, the formation stage carried was out.

In the second part of the experiment, modeling electromechanical two post lifts was conducted.

In the first phase of modeling, the discussed products, parts were modeled and standard machine elements were selected. The proposed procedure leads to the possibility of redesigning parts in case of changing parameters.

In the second and the third phase to approach the modeling of higher-level incorporation.

In the second phase was conducted modeling assemblies electromechanical two post lifts. In this paper the modeling phase assemblies is shown an example of a higher level assembly of the threaded pair electromechanical two post lifts.

The first step is carried out functional analysis of higher-level assembly of threaded pairs electromechanical two post lifts and defines the appropriate parts and subassemblies of the same assemblies.

Research and design in commerce & industry 8(2010)4, 188

Figure 6. Mobile carrier console - subassembly

In the next step, using a tool for matching and definition of constraints was formed the final model of the assembly of threaded pairs electromechanical two post lifts, figure 7.

The analysis of constraints of modeled assembly threaded pair in Inventor, using options Drive Constraint. Revealed the overextended constraints are removed.

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Revealed the overextended constraints are removed.

Figure 7. Assembly of threaded pairs

By analogy, using appropriate tools for matching and definition of constraints, were other assemblies modeled.

Furthermore, the modeled assembly threaded pairs are first used to model higher-level assembly of the driving and following columns, and then the main assembly of electromechanical two post lifts. Some examples of complex matching of higher levels of incorporation components for the assembly of electromechanical two post lifts are: • • • •

contact the wheels mobile carriers consoles and columns, belt drive, chain drive, and connection between console and mobile carriers console.

The third phase was carried out modeling of the main assembly of electromechanical two post lifts. The first step is carried out functional analysis of a higher level of incorporation of the main assembly of electromechanical two post lifts and defined its corresponding angles parts, subassemblies and assemblies. In the second step, the first fixed component is selected and imported into the Assembly Modeler, and then imported into the free components Assembly Modeler.

The base lifts is selected for a fixed component.

Free list of imported components consisted of the further components: driving column, following column, telescopic console, electric motor, driving pulleys, following pulleys, sling etc. Because of the limited space of this paper, figure 8 shows the final model of the main assembly of electromechanical two post lifts.

In the final step of this experiment is an analysis of the constraints of the main assemblies model in Inventor, using option Drive Constraint.

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Figure 8. Main assembly of electromechanical two post lifts

The validity of the created model electromechanical two post lifts, and therefore the validity of the proposed procedures for modeling the higher level of incorporation, confirmed the following activities: •

•

•

simulation analysis of assemblies and main assembly the electromechanical two post lifts, import 3D geometry electromechanical two post lifts the program ANSYS and the formation of finite element model, and static and dynamic analysis of finite element model formed.

During the experiment is shown: • • • •

modeling high-level incorporation was done according to the most logical order, problems have not reported in the phases of modeling the higher level of incorporation, modeling of higher levels of incorporation worked effectively, and performed parts, assemblies and the main assemblies were adequate substitute for a physical prototype.

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CONCLUSION

REFERENCES

The software package Inventor, modeling the higher level of incorporation according to the proposed procedure, illustrated by the example of electromechanical two post lifts. For the illustrated example, the proposed modeling concept proved to be effective and based on that in this paper strongly recommends the same concept to model higher levels of incorporation with other assemblies.

1) http://www.teamcad.co.rs

First, based on the exposed examples of modeling a higher level of incorporation, which is also an experiment, it was shown that the phase of modeling conducted two activities, matching components and definition of constraints, which can accomplish separately or simultaneously.

Further, during the implementation of this example it is shown that errors can occur and the collision which further block the simulation analysis on the model. Guidelines for their detection and removal are given.

The existence of various kinematic relations and complex interactions between the columns and the mechanism for lifting, assembly of electromechanical two post lifts seems relevant to the verification of the proposed procedure.

2) Krsmanović, C., Anderla, A., Rafa, K. (2008) Procedures and Methods of Mating and Constraints Definition in Computer Aided Assembly Design Processes, Journal of Mechanical Engineering Design, 11(1), 31-44 3) Madsen, D. (2003) Autodesk Inventor 5/5.3, Belgrade: Cet Computer Equipment and Trade.

4) Perišić, S. (2009) Prelazak u višu klasu, PC PRESS, 15 (158), 94-97 5) Stojković, M., Trajanović, M., Korunović, N., (2005) Računarom podržano projektovanje pneumatika, Istraživanja i projektovanja za privredu, 3 (8), 19-32 6) Vasiljević, R. (2009) Dinamička analiza elektromehaničke dvostubne dizalice, Mašinski fakultet Beograd Paper sent to revision: 29.09.2010 Paper ready for publication: 10.11.2010.

For more complex products and assemblies, based on the experiences of the authors of this paper, there may be special cases when the tool suite Inventor, and other software solutions in the CAD group, do not support defining complex kinematic relations between its components. It will be necessary to resort to artificial definition of working references to pairs of components (for example points, lines or surfaces).

From these conclusions, which are the results of the conducted examples, derive the appropriate advice and recommendations that may be useful to students of mechanical engineering and mechanical engineers-designers which are dealing in product modeling.

Research and design in commerce & industry 8(2010)4, 188

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EVENTS REVIEW 6 th IIPP QUALITY MANAGEMENT SCHOOL 30.10.2010. - Belgrade 04. - 06.2010. - Zlatibor Considering business conditions of European market, quality has a significant role, not only in providing new markets, but also in maintaining the existing ones. Nowadays, customers do not only expect a quality product, but they require a proof that the company is capable to produce high quality products and provide quality services. Obtaining of this evidence should be the first goal for each company that has high aspirations when it comes to new markets and in order to maintain its reputation. Implementation is not complete if employees are not inform about standards.

With the aim to closer inform the employees of the meaning and significance of ISO standards, Institute for research and design in commerce & industry – IIPP has organized training “School of Quality”.

During the training participants: • expended their knowledge about implementation of ISO standards, • learned how to maintain and improve quality level of companies • learned how to verify and improve business performance of companies Training was held during five days in two locations. First lectures were held at the Faculty of Mechanical Engineering in Belgrade, while the final lecture and the test took place in the beautiful ambience of the hotel STC Zlatibor at mountain Zlatibor.

Programme • Fundamentals of quality concepts, definitions, approaches • Standards, review and interpretation • Management Responsibility • System and process approach • Data management, information system • Statistical methods (engineering methods, quality management methods) • RISK, FMEA, FTA • Supply and storage, evaluation of supplier • Maintenance • Evaluation, audit, certification • Examples, practice, Deming management experiment • PAS 99 - Integrated Management Systems Result After implemented training, Qiipp consultant is able to assume responsibility for independent work in the following fields of activity: • Implementation of quality standards • Maintaining a high level of quality • Constant improvement of the quality system • Assessment and audits of own companies and their suppliers Candidates who passed the test were given a diploma “Qiipp consultant for implementation, maintenance, analysis, evaluation and testing, design and improvement of the quality system”.

Next cycle of training “Quality school” will be held during March 2011.

Information: www.iipp.rs

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EVENTS REVIEW 11 th IIPP MAINTENANCE MANAGEMENT SCHOOL 30.10.2010. - Belgrade 04. - 06.2010. - Zlatibor Traditional autumn cycle of Maintenance Management School was another unique opportunity to expand knowledge in the field of technical systems maintenance.

This year, training was held from October 30th till November 6th 2010. During these five days focus was given to the following topics: •

Maintenance Objectives and Policies

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Maintenance Concepts

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Maintenance Terminology

•

Laws and Regulations

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Condition Monitoring

•

Fault Finding Techniques

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Spare Part Management

•

Corporate/Company Environment

•

Work Planning

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Team Working and Communications

•

Information Technology

•

Quality Assurance (Systems)

•

Environment and Occupational Health and Safety

The school program merges best local knowledge and experience modernized and harmonized with the recommendations of European Federation of National Maintenance Societies.

Since Maintenance Management School connected and unified local tradition and experience in the maintenance process with the European norms and requirements, it’s result is thus twofold - to all who signed up gives a chance to gain national certificate ’’Expert for maintenance management” and to those who can and want more, Maintenance management school opens the possibility of obtaining the International certificate “European maintenance manager”.

“Maintenance Management School” has been organized for 11 cycles in a row. Result of this training that has been held twice a year in the last five and half years is more than 240 national certificates and 16 internationally recognized certificates European Maintenance Manger.

Presented practical experience in combination with adopted theoretical knowledge creates experts for maintenance management are capable to perform and coordinate the maintenance of complex technical systems.

Next cycle of Maintenance Management School will be held during the spring 2011.

Information: Institute for research and design in commerce & industry Jurija Gagarina 12b, 11070 New Belgrade t. +381 11 6300750 f. +381 11 6300751 www.iipp.rs Research and design in commerce & industry 8(2010)4

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EVENTS REVIEW PNEUMATICI 2010 04. - 05.2010. - Zlatibor Hotel STC “Zlatibor”, situated on the Zlatibor mountain, hosted the sixth conference “Pneumatici 2010” on 4 and 5 of November. This Conference was organised by University of Belgrade – Faculty of Forestry, Serbian Chamber of Commerce, iipp – Institute for research and design in commerce & industry and Serbian Maintenance Society – DOTS. The Conference organization was supported by the Government of Serbia - Ministry of Technology and Science.

39 (national) experts in the area of pneumatics, including members of universities, scientific institutes, representatives from tire factories, domestic transport companies, import companies, and commercial and public sectors attended the Conference.

Universities of Belgrade, Niš, and Kragujevac, the Institute for organic and physical chemistry from Belgrade, Republic of Serbia – Intellectual Property Office, “Lasta” Transport Company from Belgrade and the biggest domestic tyre producer “Tigar Tires” from Pirot presented total of 15 papers.

The Conference was opened by Dr Gradimir Danon, who talked about the current situation and recent trends in the tire development and production worldwide. The paper underlines the need for research regardless of the current crisis. A positive example is a true green tyre to be made out of natural and recycled materials. The next speaker was Mr. Šošević from Serbian Chamber of Commerce presenting the situation in the tire industry and set of measures for improvement in this area.

The lecture that caught most of the attention, work of Prof. Plavšić and Dr. Lazić, gave a new theoretical approach to particle interaction on nano-level and granular morphology all together. This work represents a basis for deepening the knowledge about interaction in composite elastic materials used in tyre production.

After the plenary lectures, the meeting was divided in two sections. In the first section, papers were presented by researchers from universities of Belgrade, Niš and Kragujevac. Mr. Korunović and Mr. Stojković from University of Niš showed their research in the field of tire modelling encompassing an advanced procedure for pre-processing of CAE model and an extended tire model, with its role, among others, to be used for tire/drum rolling analysis. The authors from Kragujevac, presented a portable device for tire/road coefficient of friction measurements. This device was developed at the Automobile Institute from Kragujevac. The obtained measured values may be used for calculations or as the input values to simulation programs. Mrs. Popović from the Environment Protection Agency rounded up this section with a talk on the importance of patent protection and gave an insight about patent protection on Tire Pressure Monitoring Systems (TPMS) in Serbia and abroad.

The other section of the Conference was about research in the exploitation and maintenance. Mr. Petrović and Mr. Gavrić presented the methods of technical maintenance of tires in “Lasta” Transport Company. They provided an analysis of the cost of tires consider specific examples. In his lecture, Prof. Mitrovic presented the practical experience with TMPS systems on cars and buses with the intention of justifying its benefits. Prof. Mitrović presented the equation that should enable checking of the feasibility of TMPS devices on the different vehicles.

An open discussion on “Winter Tires” finished the Conference with very notable introductory lecture

by Mr. Manić from “Tigar Tires” from Pirot.

The Conference participants received Proceedings on CD with the peer-reviewed and accepted papers.

Prof. dr Gradimir Danon

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Research and design in commerce & industry 8(2010)4

BOOK RECOMMENDATION ELECTRIC VEHICLES IN THE WORLD AND IN SERBIA

By Zoran Nikolić The interests for clean power systems and protection of global and urban environment are today the most important tasks of society. It relates to a large instant to all transportation systems, in particularly to motor vehicles. The monograph ELECTRIC VEHICLES IN THE WORLD AND IN SERBIA presents a comprehensive review of the development of electrically powered vehicles in last several decades, in the world and in Serbia.

In the first section the influences of road transportation on environment is analyzed, pointing out the preferences of electrical prime movers for rod vehicles, both with regard to environment protections, economy and vehicles performances. It is followed by a concise review of electric vehicles development, from the very beginning (1839), through the development caused by known oil crisis to present days, characterized by strong demands regarding environment protection. The third section describes the most important components of electric vehicles, namely batteries, motors, control units and necessarily accessories. The modern concepts of all these components prove that in this filed of engineering a tremendous progress is achieved in lat several years. It particularly relates to batteries, which are in detailed analyzed in the forth section. Along with that, in the fifth section are presented different concepts of hybrid power units, combining classical internal combustion engines with electro motors in an efficient power system, overcoming most of shortages of each power unit separately. A separate section (the seventh) is devoted to the calculation and prediction of electric vehicles performances, followed by comments on corresponding national and international regulations, especially with regard to vehicle safety.

Next several sections review the development of various electric vehicles achieved in the world, in different countries and by different manufacturers, including the most important on the world market... Separately are presented designs of very light passenger vehicles (including bicycles, motor chairs, etc), electric cars, commuter and delivery vehicles, electro buses, as well as various designs and concepts of hybrid electro cars and buses.

The final five sections are devoted to the development of electric vehicles in Serbia. The very beginning of these activities is organized by academic A. Despic in the frame of the Serbian Academy of Science and Arts in 1973. The Bureau for Electric Vehicles formed for this project gathered a couple of electrical, electrochemical and mechanical engineers and experts in economy. The result of their work was the first home made electric van for bread delivery (1974), on the TAM chassis, with all components produced in Serbia, mostly according to requirements defined by the Bureau. This vehicle which was thoroughly tested in laboratory and under usage conditions and results obtained were satisfactory. These first encouraging results attracted several companies, like CRVENA ZASTAVA and others, so after some years, with an important participation of Bureau, several electric vehicles for different purposes were developed.

Publisher: INSTITUT GOSA, Beograd, Milana Rakica 35 Number of pages: 312 Publication date: 2010 ISBN: 978-86-86917-O7-O7-2, Research and design in commerce & industry 8(2010)4

Prof. dr Jovan Todorović

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INSTRUCTIONS FOR AUTHORS Send to: Institut za istraživanja i projektovanja u privredi Jurija Gagarina 12b, 11 070 Novi Beograd Phone: +381 11 6300750 Fax: +381 11 6300751 E-mail: nstanojevic@iipp.rs; astevanic@iipp.rs All manuscripts must be in English free of typing errors (please use Spell Checking).The maximum length of contributions is 10 pages.

Every manuscript submitted to IIPP will be considered only if the results contained in the paper were not already published, that are not currently in the process of publishing and not to be published in another journal. Each paper is sent to a review by two independent experts and the authors are obligated to adopt the observations and comments of the reviewers.

THE FORMAT OF THE MANUSCRIPT The manuscript should be written in the following format: • A Title, which adequately describes the content of the manuscript.

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• References, which must be cited consecutively in the text using brackets /1/ and collected together in a reference list at the end of the manuscript.

Units - standard SI symbols and abbreviations should be used.

Abbreviations should be spelt out in full on first appearance, e.g., variable time geometry (VTG).

Meaning of symbols and units belonging to symbols should be explained in each case or quoted in a special table at the end of the manuscript before References Figures must be cited in a consecutive numerical order in the text and referred to in both the text and the caption as Fig. 1, Fig. 2, etc. Figures should be prepared without borders and on white grounding and should be sent separately in their original formats.

Pictures may be saved in resolution good enough for printing in any common format, e.g. BMP, GIF or JPG. Tables should carry separate titles and must be numbered in consecutive numerical order in the text and referred to in both the text and the caption as Table 1, Table 2, etc. The tables should each have a heading. Tables should not duplicate data found elsewhere in the manuscript.

Acknowledgement of collaboration or preparation assistance may be included before References.

Please note the source of funding for the research.

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Research and design in commerce & industry 8(2010)4

INSTRUCTIONS FOR AUTHORS REFERENCES must be written in the following form: Journal: /Number/ (must match number in the text), Last name, Initial of the authors name, (Year of publication). Article title: secondary title. Title of the Journal (italic), volume number (number of the journal), page number. // Petrović, G., Petrović, N., Marinković, Z. (2008). Primena teorije Markova u mrežnim sistemima masovnog opsluživanja. FACTA UNIVERSITATIS Series Mechanical Engineering, 6 (1), 45 – 56.

Book: /Number/ (must match number in the text), Last name, Initial of the authors name, (Year of publication) Book title: secondary title, Place of publishing: Publisher. /2/ Vasić, B., Popović, V. (2007) Inženjerske metode menadžmenta, Beograd: Institut za istraživanja i projektovanja u privredi.

Book chapter: /Number/ (must match number in the text), Last name, Initial of the authors name, (Year of publication) Chapter title: secondary title, Book title: secondary title, Place of publishing: Publisher, page numbers. /3/ Vasić, B. (2004) Model Hardverskog resursa, Menadžment i inženjering u održavanju, Beograd: Institut za istraživanja i projektovanja u privredi, 95 – 97.

Internet source: /Number/ (must match number in the text), link to the page from which the text is taken, retrieved on (state the date) /4/ http://www.autogume.net/veleprodaje/kelena/, retrieved on November 7th, 2010 INDEXING Starting from 2006., only three years since the launch of the journal “Research and design in commerce & industry“, all published articles are indexed in international ELSEVIER database through SCOPUS service. In this way, the work and results of the local scientiest are widely available as the SCOPUS is the largest database of abstracts and citations in terms of scientific publications and quality web sources which, above all, give the results of research in various fields.This database provides excellent information necessary for further work and scientists training with extensive search capabilities.

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SADRŽAJ Od uređivačkog odbora Dr Miodrag Zec KLJUČNE DISPROPORCIJE U SRBIJI I ODRŽIVI RAZVOJ

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Rezimei radova Dr Stevan Maksimović, Marija Blažić, Mirko Maksimović PROJEKTOVANJE KONSTRUKCIJA SA ASPEKTA ZAMORA I MEHANIKE LOMA

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Christian Sahr, Lutz Berger LANČANE INTERAKCIJE ENERGETSKE APSORPCIJE

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Lutz Eckstein, Sven Faßbender, Micha Lesemann, Leif Ickert, Bastian Hartmann, Markus Bröckerhoff “AUTO ZA SVE” – TAKMIČENJE ZA KONCEPT VOZILA FORD MODEL T

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Dr Vladimir Popović, dr Branko Vasić, dr Dejan Curović JEDAN MOGUĆI ODGOVOR NA PITANJE: ŠTA JE UPRAVLJANJE SREDSTVIMA?

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Mr Rade Vasiljević VIŠI NIVOI MODELIRANJA NA BAZI SOFTVERA INVENTOR

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OD UREĐIVAČKOG ODBORA

Ključne disproporcije u Srbiji i održivi razvoj Srbija je nažalost danas po ključnim segmentima posmatrano nedovršena država sa brojnim otvorenim pitanjima teritorijalne organizacije, političkog modela i ekonomskog mehanizma kojim se može finansirati održivi razvoj i uspostaviti novi okvir vrednosnog sistema u društvu. Dugogodišnje odlaganje istinskih i celovitih reformi vodilo je kumuliranju mnogobrojnih disproporcija od kojih navodimo sledeće: Prvo, disproporcija između ukupne proizvodnje i neprekidno rastuće potrošnje stvorila je rastući jaz koji se pokriva donacijama, doznakama, privatizacionim prihodima, novim zaduživanjem države, javnih i privatnih preduzeća, stanovništva i visokom stopom inflacije. Vladajući establišment je konačno priznao da je Prof. dr Miodrag Zec model zasnovan na rastu potrošnje „iscrpeo svoje mogućnosti“, odnosno da je pogrešan i neodrživ na duži rok. Dramatično deluje saznanje da je nivo industrijske proizvodnje ostvaren 2009. godine iznosi oko 50% nivoa dostignutog 1990. godine. Za zemlju naše veličine, položaja i raspoloživih resursa porazno deluje saznanje da industrija učestvuje u stvaranju BDP manje od jedne petine.

Drugo, disproporcija između domaće akumulacije i nivoa neophodnih investicija vodi odlaganju investicija, a kada je to nemoguće, novim zaduživanjem pod sve nepovoljnijim uslovima. Kriza formiranja akumulacije ranije pripisivana strateškim slabostima koncepta društvene svojine nastavlja se i posle privatizacije privrede što pokazuje da nedostatak sklonosti društva ka štednji ( akumulaciji) pored sistemskog ima i endemski karakter. Ključni preokret u društvu će nastupiti kada štednja bude ugaoni kamen javne i privatne vrline, kada se eliminiše inflaciono obezvređivanje štednje i borba za dužnički dobitak.

Treće, disproporcija između uvoza i izvoza stvara neodrživi jaz koji se pokriva novim zaduživanjem, pritiskom da se održi devizni kurs što dalje stvara nemogućnost razvoja domaće proizvodnje i u nedostatku novih priliva kapitala ozbiljno povećava javni i ukupan dug prema inostranstvu, vrši pritisak na kreditni rejting, dramatizuje stanje deviznih rezervi i ugrožava spoljnu likvidnost zemlje. Četvrto, disproporcija između aktivnog i izdržavanog stanovništva se neprekidno pogoršava i pored toga što stanovništvo nema prirast već se smanjuje ( od 30.000- 45.000 godišnje) . Kod nas se urušava biološki potencijal jer rast broja izdržavanog stanovništva nije posledica visokog nataliteta (rasta populacije do 18 godina), već rasta kontingenta izdržavanog stanovništva koji se nalazi u najboljem radnom periodu ( od 18 do 50 godina).

Peto, disproporcija zaposlenih i nezaposlenih kako agregatno tako i strukturno uz stopu stvarne nezaposlenosti od oko 20%, a odliv školovanih u inostranstvo i nezadovoljavajuću kvalifikacionu strukturu na tržištu rada otvara pitanje ko će raditi ako ikada počnu investicije u realni sektor ( indistriju). Šesto, disproporcija između zaposlenih u administraciji i proizvodnom sektoru i sistem nagrađivanja sugeriše najkreativnijem delu populacije da se usmeri na traženje posla van industrije.

Sedmo, disproporcija između zaposlenih u nerazmenskom sektoru (banke, trgovina,usluge) i u razmenskom sektoru (industrija i poljoprivreda) dodatno odvlači najtalentovanije studente prirodnih nauka (fizika, matematika, tehnika) u nerazmenski sektor koji ne doprinosi ekspaziji proizvodnje i izvoza već prodaji tuđeg novca i tuđih roba na domaćem tržištu.

Osmo, disproporcija između broja zaposlenih (naročito u razmenskom sektoru) i broja penzionera u uslovima nepostojanja kapitala penzionih fondova zahteva stalne intervencije iz budžeta prema penzionom sistemu što dovodi do neodrživosti penzionog sistema i čitavog drugog niza stečenih prava.

Deveto, disproporcija između razvijenih i nerazvijenih regiona se povećava uprkos činjenici da se već 60 godina vodi intenzivna politika ravnomernog regionalnog razvoja i u tu svrhu troše ogromna Research and design in commerce & industry 8(2010)4,

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budžetska sredstva. U datim okolnostima problemi regionalnog razvoja se politički odražavaju i od ekonomskog postaju državno i teritorijalno pitanje.

Deseto, disproporcija između ultra- bogatih i ultra-siromašnih je drastičnija u Srbiji nego u ostatku Evrope, uključujući i susedne zemlje u kojima goruće pitanje nije toliko veličina bogatstva ( mada je ono zamašno i stečeno uz korišćenje defekata ili pak namere sistema) već dubina siromaštva koje može trajno destabilizovati održivi razvoj. U takvim okolnostima pritisak na preraspodelu već postojeće imovine može da potisne u drugi plan stvaranje uslova za izlazak iz siromaštva putem stvaranja novog bogatstva. Bez pretpostavki da mehanizam stvaranja novog „bogatstva naroda“ zameni više puta primenjeni obrazac preraspodele već postojećeg bogatstva neće se postići socijalna stabilnost bez koje nema ekonomskog prosperiteta. Korigovanje sistema poreza i stimulisanje produktivnog ulaganja je pretpostavka da se promeni imovinski portfolio pojedinca, preduzeća i države kao baza za racionalan ekonomski i prihvatljiv socijalno politički sistem.

Srpsko društvo mora da se ozbiljno pozabavi neprekidnim kumuliranjem navedenih disproporcija i preduzme radikalne korake da ih zaustavi i radikalno preokrene. Nesumnjivo je da koren preokreta i temelj održivog razvoja mora biti promena ekonomskog modela i mera tekuće ekonomske politike.

Srbija kao mala zemlja može popraviti svoje mesto u svetskoj privredi samo povećanjem proizvodnje, smanjivanjem tekuće potrošnje i usmeravanjem tako formiranog viška u kapitalne investicije.

Takav pristup otvara put prema pozitivnom trgovinskom bilansu i stvaranju osnove za postepeno smanjivanje spoljnog duga. Kreiranje nove strukture društvenog bruto proizvoda ( rast proizvodnje i izvoza) i novi principi njegove raspodele ( favorizovanje štednje i investicija nasuprot tekućoj potrošnji) stvoriće osnovu za promenu odnosa aktivnog i izdržavanog stanovništva, novu socijalnu konfiguraciju i preokret prema ravnomernijoj regionalnoj razvijenosti. U novim prilikama verovatno je očekivati promenu demografskih trendova ili pak radikalnije useljavanje radno aktivnog stanovništva umesto iseljavanja. Nastavljanje dosadašnjih trendova gde svi kvalitativni parametri razvoja beleže pad, a smanjivanje populacije prati visoka nezaposlenost mladih i školovanih ljudi i njihovo iseljavanje nesumnjivo je znak dubokih poremećaja i alarm za hitno preduzimanje mera za krupne promene.

Novi obrazac privrednog razvoja zahteva novi vrednosni koncept društva kao celine čime se stiču pretpostavke za racionalan ekonomski model i jeftinu i funkcionalnu državu.

Prof. dr Miodrag Zec

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REZIMEI RADOVA Paper number: 8(2010)3,184

PROJEKTOVANJE KONSTRUKCIJA SA ASPEKTA ZAMORA I MEHANIKE LOMA Prof. dr Stevan Maksimović - Vojnotehnički institute, Beograd Marija Blažić - Vojnotehnički institute, Beograd Mirko Maksimović - JKP Beogradski vodovod i kanalizacija Pažnja u radu je usmerena na razvoj proračunskih procedura pri projektovanju letelica sa aspekta zamora i mehanike loma. U radu su uspostavljeni analitički izrazi za faktore intenziteta napona (FIN) u trodimenzionim (3-D) strukturalnim elementima kao i za analizu širenja prskotina. Oštećenja su definisana u obliku polu-elipse na površini strukturalnog elementa opterećenog cikličnim opterećenjima konstantne amplitude i spektrom opterećenja. Rezultati uspostavljenog analitičkog modela za FIN su upoređeni sa rezultatima MKE gde je dobijena dobra saglasnost.Proračun čvrstoće sa aspekta mehanike loma je ilustrovan na problemu nosne noge lakog školskog aviona.

Ključne reči: Zamor konstrukcija, mehanika loma, Prskotine u 3-D telima, Analitički model, Procena veka, Metalne konstrukcije.

Slika 3. Strukturalni model nosne noge lakog školskog aviona

Slika 4. Model konačnih elemenata nosne noge lakog školskog aviona

Paper number: 8(2010)3,185

LANČANE INTERAKCIJE ENERGETSKE APSORPCIJE Christian Sahr - Institut za automobilske tehnike, Nemačka Lutz Berger - Institut za automobilske tehnike, Nemačka Zaštita putnika i posebno zaštita pešaka postaju od velikog značajnija u poslednjih nekoliko godina. Razlog toga je nedovoljna bezbednost pešaka i teške povrede prilikom sudara sa vozilima. Za smanjenje broja povreda i njihove težine, neophodne su promene dizajna frontalne strukture vozila koje bi absorbovale energiju i smanjile snagu i ubrzanje prilikom udara pešaka. Zbog toga se sve više i više takvih struktura za apsorpciju energije dizajnira od različitih materijala kao što su visoko porozne pene, energetski amortizeri sa plastičnom deformacijom ponašanja kao što su strukture jajastog oblika. Kombinacija tih delova deluje pod opterečenjem usled nesreće, na pr. Branik sistem.

Za izgled novog zaštitnog sistema, neophodno je predvideti ponašanje deformacije i nivo sile tih Research and design in commerce & industry 8(2010)4,

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REZIMEI RADOVA „lančanih interakcija“.

Osnovni cilj ove studije, zajedno sa Institutom za kompozitne materijale u Kajzer- slauternu, je da otkrije i kvantifikuje interakcije između struktunih komponenti u složenim sistemima, koje se odigravaju tokom uticaja nisko-energetskih događaja. Sobzirom da ove interakcije često dovode do odstupanja između eksperimentalnih i simulacionih rezultata, tačnost prognoza nesreće dobijenih simulacijom će se povećati kao i posledice ovog istraživanja.

Sistem energetske apsorpcije, koji je istraživan u okviru ove studije, pokazuje lančane interakcije različitih konstitutivnih komponenti: EPP pena, polimerna jajasta struktura, čelični i aluminijumski listovi.. Ove lančane interakcije i njene sastavne komponente su istraživani eksperimentalno i dalje modelirani po uzoru na konačne elemente kod LS-Dyna. Sopstveni eksperimentalni podaci materijala podaci se koriste za proveru modela materijala.

Ključne reči: Inženjering materijala, EPP – pena, jajasta kutija, numeričke simulacije, energetska apsorpcija, provera ispravnosti, modeliranje, testiranje, zaštita pešaka, kompleksni uticaji procesa.

Paper number: 8(2010)3,186

“AUTO ZA SVE” – TAKMIČENJE ZA KONCEPT VOZILA FORD MODEL T Lutz Eckstein - Institut za automobilske tehnike, Nemačka Sven Faßbender - Institut za automobilske tehnike, Nemačka Micha Lesemann - Institut za automobilske tehnike, Nemačka Leif Ickert - Institut za automobilske tehnike, Nemačka Bastian Hartmann - Institut za automobilske tehnike, Nemačka Markus Bröckerhoff - Institut za automobilske tehnike, Nemačka Timu Instituta za automobilske tehnike- Institut für Kraftfahrzeuge (IKA), RWTH Aachen univerziteta, bilo je potrebno samo tri meseca da razvije inovativni koncept vozila koje je sposobno da nosi konvencionalne kao i alternativne pogonske module zahvaljujući dizajnu koji je moguće menjati u razmeri – savremeni „auto za svakoga“ za 2015. godinu sa osnovnom prodajnom cenom manjom od 7000 dolara.

Ključne reči: Zahtevi koncepta, razvoj koncepta, tehničke specifikacije,optimizacija topologije, pogonski sistem

Slika 1. Ford Model T

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REZIMEI RADOVA Paper number: 8(2010)3,187

JEDAN MOGUĆI ODGOVOR NA PITANjE: ŠTA JE UPRAVLjANjE SREDSTVIMA? Dr Vladimir Popović – Mašinski fakultet u Beogradu Dr Branko Vasić – Mašinski fakultet u Beogradu Dr Dejan Curović – Mašinski fakultet u Beogradu Upravljanje sredstvima (Asset Management) je kulminacija duge istorije razvoja upravljanja fizičkim sredstvima. Ono se fokusira na postizanje određenog nivoa usluge, oblike rizika i finansijske zahteve, koji su prihvatljivi za deoničare (vlasnike), tokom životnog ciklusa tih sredstava. Upravljanje sredstvima uključuje donošenje odluka o merama koje se preduzimaju prema fizičkim sredstvima radi postizanja gore navedenih ciljeva, i često može podrazumevati pravljenje kompromisa između kratkoročnih i dugoročnih dobiti. Dobro upravljanje sredstvima tiče se opravdanosti odluka koje su zasnovane na dostupnim informacijama i podrazumeva upotrebu adekvatnih alata i tehnika za određivanje optimalnog balansa između troškova i rizika koji su bitni za sve aktivnosti životnog ciklusa sredstava. Obezbeđivanje da organizacije dobro upravljaju sredstvima je od sve većeg interesa i značaja, ne samo za same organizacije, koje kao rezultat imaju veliku uštedu novca i bolje kontrolišu rizike, već i za državu i korisnike koji traže maksimalnu vrednost za svoj novac, kao i standardno dobar kvalitet usluge, ne samo u ovom trenutku, već i u budućnosti. Razumevanje, merenje i unapređenje sposobnosti upravljanja sredstvima je, stoga, od sve većeg značaja.

Ključne reči: Upravljanje sredstvima; Održavanje

Paper number: 8(2010)3,188

VIŠI NIVOI MODELIRANJA NA BAZI SOFTVERA INVENTOR Mr Rade Vasiljević – IRC NIC A.D., Užice U ovom radu su analizirani viši nivoi modeliranja, koji u mašinskom projektovanju i analizi proizvoda predstavljaju jednu od najsloženijih i najzahtevnijih faza. U toj fazi inženjer-projektant troši dosta vremena na uparivanje delova u sklopu i definisanje zahtevanih ograničenja. Sa jedne strane, skraćenje ovog vremena ne postiže se ni upotrebom danas najmoćnijih softverskih alata, dok se, sa druge strane dodatno povećava bez postojanja eksplicitnih procedura. Za optimizovanje vremena potrebnog pri modeliranju viših nivoa ugradnje predložena je procedura u formi strukturnog dijagrama. Na sistematičan način predstavljeno je softversko rešenje Inventor. Poseban akcenat je dat višim nivoima modeliranja. Rešavanje viših nivoa modeliranja, primenom Inventora, je ilustrovano na konkretnom primeru sklopa.

Ključne reči: viši nivoi modeliranja, inventor, sklop, uparivanje, ograničenja

Slika 5. Navojno vreteno - deo Research and design in commerce & industry 8(2010)4,

Slika 6. Sklop navojnog para

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Research and design in commerce & industry 8(2010)4