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Fatigue Life Prediction and Modeling of Elastomeric Components

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Fatigue Life Prediction and Modeling of Elastomeric Components A Dissertation Entitled Fatigue Life Prediction and Modeling of Elastomeric Components by Touhid Zarrin-Ghalami Submitted to the Graduate Faculty as partial fulfillment of the requirements for the Doctor of Philosophy Degree in Engineering Dr. Ali Fatemi, Committee Chair Dr. Efstratios Nikolaidis, Committee Member Dr. Mehdi Pourazady, Committee Member Dr. Vijay Goel, Committee Member Dr. Yong Gan, Committee Member Dr. Patricia R. Komuniecki, Dean College of Graduate Studies The University of Toledo May 2013 i Copyright 2013, Touhid Zarrin-Ghalami This document is copyrighted material. Under copyright law, no parts of this document may be reproduced without the expressed permission of the author. ii An Abstract of Fatigue Life Prediction and Modeling of Elastomeric Components by Touhid Zarrin-Ghalami Submitted to the Graduate Faculty as partial fulfillment of the requirements for the Doctor of Philosophy Degree in Engineering The University of Toledo May 2013 This study investigates constitutive behavior, material properties and fatigue damage under constant and variable amplitude uniaxial and multiaxial loading conditions, with the goal of developing CAE analytical techniques for durability and life prediction of elastomeric components. Such techniques involve various topics including material monotonic and cyclic deformation behaviors, proper knowledge of stress/strain histories, fatigue damage quantification parameters, efficient event identification methods, and damage accumulation rules. Elastomeric components are widely used in many applications, including automobiles due to their good damping and energy absorption characteristics. The type of loading normally encountered by these components in service is variable amplitude cyclic loading. Therefore, fatigue failure is a major consideration in their design and availability of an effective technique to predict fatigue life under complex loading is very valuable to the design procedure. In this work a fatigue life prediction methodology for rubber components is developed which is then verified by means of analysis and testing iii of an automobile cradle mount made of filled natural rubber. The methodology was validated with component testing under different loading conditions including constant and variable amplitude in-phase and out-of-phase axial-torsion experiments. The analysis conducted includes constitutive behavior representation of the material, finite element analysis of the component, and a fatigue damage parameter for life predictions. In addition, capabilities of Rainflow cycle counting procedure and Miner’s linear cumulative damage rule are evaluated. Fatigue characterization typically includes both crack nucleation and crack growth. Therefore, relevant material deformation and fatigue properties are obtained from experiments conducted under stress states of simple tension and planar tension. For component life predictions, both fatigue crack initiation approach as well as fatigue crack growth approach based on fracture mechanics are presented. Crack initiation life prediction was performed using different damage criteria. The optimum method for crack initiation life prediction for complex multiaxial variable amplitude loading was found to be a critical plane approach based on maximum normal strain plane and damage quantification by cracking energy density on that plane. The fracture mechanics approach was used for total fatigue life prediction of the component based on specimen crack growth data and FE simulation results. Total fatigue life prediction results showed good agreement with experiments for all of the loading conditions considered. iv This dissertation is dedicated to my dear parents, Jila and Siawash. v Acknowledgements I would like to sincerely thank my dear advisor, Prof. Ali Fatemi, who has supported me throughout this long route with his knowledge, patience and useful hints. This work could not be completed without his guidance, encouragement and advice during long meetings, almost daily, and lots of emails. Dr. Yong Gan, Dr. Mehdi Pourazady, Dr. Efstratios Nikolaidis, and Dr. Vijay Goel are highly appreciated for serving on my Ph.D. committee. I would also like to thank Chrysler Group LLC and specifically Dr. Yung-Li Lee for funding the project and Paulstra CRC for providing the components and FE model. The time and effort of Mr. John Jaegly, Mr. Randall Reihing and Mr. Tim Grivanos from the machine shop of the MIME Department for helping in making different fixtures for uniaxial and multiaxial testing of the components is highly acknowledged as well. I would also like to thank my colleagues at the fatigue and fracture research laboratory of the University of Toledo for their help, support and efforts during this period of hard working. I would also like to thank Ms. Debbie Kraftchick and Ms. Emily Lewandowski in the MIME department office for their help in providing the requirements of this study. Finally, I would like to thank my dear parents and sisters for all their support and encouragement throughout my education from the very beginning to doctorate degree. vi Table of Contents Abstract .............................................................................................................................. iii Acknowledgements ............................................................................................................ vi Table of Contents .............................................................................................................. vii List of Tables…… ............................................................................................................. xi List of Figures ................................................................................................................... xii List of Abbreviations ...................................................................................................... xvii List of Symbols ................................................................................................................ xix 1 Introduction…… ....................................................................................................1 1.1 Preview…. .........................................................................................................1 1.2 Motivation for the study and objectives.............................................................3 1.3 Outline…............................................................................................................5 2 Literature Survey….. .............................................................................................8 2.1 Introduction ........................................................................................................8 2.2 Rubber deformation mechanisms and behavior .................................................8 2.3 Fatigue crack initiation and growth approaches ..............................................10 2.4 Multiaxial fatigue behavior and models ..........................................................14 2.5 Component fatigue testing and life prediction including FE simulations........20 2.6 Damage accumulation and cycle counting in variable amplitude loading……......................................................................................................23 vii 3 Material Characterization and Fatigue Behavior …. .......................................27 3.1 Introduction ......................................................................................................27 3.2 Material and specimens…................................................................................27 3.3 Testing equipment ............................................................................................28 3.4 Specimen test methods and procedures ...........................................................28 3.4.1 Deformation behavior characterization.............................................28 3.4.2 Constant amplitude crack initiation testing.......................................29 3.4.3 Crack growth testing .........................................................................30 3.4.4 Variable amplitude crack initiation testing .......................................33 3.5 Specimen experimental results and observations ............................................34 3.5.1 Monotonic and cyclic deformation behavior results .........................34 3.5.2 Constant amplitude crack initiation tests results ...............................36 3.5.3 Crack growth tests results .................................................................38 3.5.4 Relationship between crack growth and crack initiation approaches........................................................................................40 3.5.5 Variable amplitude crack initiation tests analysis methodology .......42 3.5.6 Variable amplitude crack initiation tests results and analysis ..........43 3.6 Conclusions ......................................................................................................45 4 Component Finite Element Model and Results …............................................65 4.1 Introduction ......................................................................................................65 4.2 Hyperelastic material deformation characterization ........................................65 4.3 Uniaxial FE model definition and specifications .............................................69 viii 4.4 Stiffness test results comparison with predictions ...........................................71
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