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Experimental Characterization and Modeling of High Strength Martensitic Steels Based on a New Distortional Hardening Model

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Experimental Characterization and Modeling of High Strength Martensitic Steels Based on a New Distortional Hardening Model EXPERIMENTAL CHARACTERIZATION AND MODELING OF HIGH STRENGTH MARTENSITIC STEELS BASED ON A NEW DISTORTIONAL HARDENING MODEL BY ELIZABETH K BARTLETT A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2018 © 2018 Elizabeth K Bartlett 2 To my daughter, Gwyneth Webb, who helps me to have fun, laugh, and love through the most difficult times in my life. 3 ACKNOWLEDGEMENTS First, I would like to thank all the members of my supervisory committee for their support. I would especially like to thank my committee chair, Prof. Oana Cazacu, for her support and constructive criticisms. It was an honor and a privilege to study her research. I would also like to thank Dr. Benoit Revil- Baudard for his expertise in numerical methods. I am so grateful for the support of the 96th Test Wing, my sponsoring facility in the Science, Mathematics, and Research for Transformation (SMART) scholarship program. Specifically, I would like to thank my commanders and supervisor, Mr. Ron Lutz, as well as, Mrs. Linda Busch and Dr. Betta Jerome. I also greatly appreciate the support of the Air Force Research Laboratory (AFRL) in the experimental characterization of Eglin steel: Dr. Geremy Kleiser and Dr. Philip Flater for their training in quasi-static testing, Dr. Brad Martin and Dr. Xu Nie for their expertise in dynamic split Hopkinson pressure bar (SHPB) testing, Dr. Rachel Abrahams and Dr. Sean Gibbons for their instruction in microscopy and material science, and Mr. Richard Harris for his expertise in material characterization at the Advanced Weapons Effects Facility (AWEF). I extend my gratitude to my friends and family for listening to me ramble on and on about subsequent yield surfaces and various hardening models. Finally, I would like to thank Gwyneth Webb, my 12-year old daughter, for her encouragement and patience over long nights and weekends in room 171 of the University of Florida (UF) Research and Engineering Education Facility (REEF). 4 TABLE OF CONTENTS PAGE ACKNOWLEDGEMENTS ..................................................................................... 4 LIST OF TABLES .................................................................................................... 7 LIST OF FIGURES .................................................................................................. 8 LIST OF ABBREVIATIONS .................................................................................... 13 ABSTRACT ......................................................................................................... 16 CHAPTER 1 INTRODUCTION ............................................................................................. 18 1.1 Background of Ultra High Strength Martensitic Steel..................... 18 1.2 Survey of the Experimental Studies on Martensitic Steels ............ 23 1.3 Eglin Steel, ES-1 ........................................................................... 32 1.4 Elastic-Plastic Modeling ................................................................. 38 1.5 Goals of Current Research ............................................................ 48 2 MICROSCOPY ................................................................................................ 50 2.1 Optical Microscopy of ES-1 ........................................................... 51 2.2 Material Characterization using SEM ............................................ 55 3 MECHANICAL CHARACTERIZATION OF ES-1 ......................................... 63 3.1 Hardness of Eglin Steel ................................................................. 63 3.2 Quasi-Static Mechanical Characterization ..................................... 65 3.3 Dynamic Experimental Characterization of Eglin Steel .................. 82 3.4 Cyclic Experimental Characterization of ES-1 ............................... 99 3.5 Summary of the Experimental Characterization of ES-1 ............. 104 4 ELASTIC-PLASTIC MODEL FOR EGLIN STEEL ..................................... 105 4.1 Development of the Yield Criterion .............................................. 105 4.2 Asymmetric Hardening ................................................................ 112 4.3 Implementing the Proposed Yield Function ................................. 137 4.4 Implications of the Proposed Yield Function ............................... 143 5 5 FINITE ELEMENT ANALYSIS ..................................................................... 145 5.1 Review of Finite Element Analysis .............................................. 145 5.2 Implementation of the Elastic-Plastic Model in FEA .................... 149 5.3 Finite Element Analysis of Ultra High Strength Martensitic Steel 151 5.4 Elastic-Plastic Model Predictions ................................................ 170 6 CONCLUSIONS AND RECOMMENDATIONS .......................................... 178 REFERENCES ................................................................................................. 184 BIOGRAPHICAL SKETCH ............................................................................... 194 6 LIST OF TABLES Table Page 1-1 Monotonic and cyclic material properties. ................................................ 30 1-2 Chemical composition by percent weight of AF-1410, SAE 4340, and ES- 1. .............................................................................................................. 33 1-3 Mechanical properties under uniaxial, quasi-static tensile loading of AF- 1410, SAE 4340, and ES-1. ..................................................................... 34 2-1 Heat treatment schedule for ES-1. ........................................................... 50 2-2 ES-1 grinding and polishing schedule. ..................................................... 51 2-3 Chemical composition of ES-1 for EDS. ................................................... 56 3-1 Eglin steel material characterization test matrix. ...................................... 63 3-2 Yield stress and quasi-static compression test data. ................................ 70 3-3 Coefficients involved in Swift and Voce Hardening Laws for ES-1. .......... 70 3-4 Summary of quasi-static tension test data................................................ 72 3-5 Hardening law parameters tensile round specimens. ............................... 73 3-6 Tension-compression asymmetry ratio of ES-1 by plastic strain. ............. 76 3-7 Hardening law parameters flat tension specimens. .................................. 77 3-8 Johnson and Cook material constants for forged, cast, and cast and HIP’d ES-1. ........................................................................................................ 94 4-1 Cazacu and Barlat yield criterion parameters. ........................................ 140 4-2 Points for linear interpolation of the Cazacu and Barlat asymmetry parameter, c. .......................................................................................... 141 5-1 Finite element analysis simulation matrix. .............................................. 152 7 LIST OF FIGURES Figure Page 1-1 Tensile yield stress vs. strain-to-failure of current steels and expected strengths of third-generation UHSS. ........................................................ 19 1-2 The unit cell of single-crystal microstructures of solid steel. ..................... 20 1-3 Illustration of plastic deformation mechanisms. ........................................ 22 1-4 The fractional strength differential parameter vs. the carbon content by percent weight for different SAE 4300 series. .......................................... 24 1-5 The effect of tempering temperature on the strength differential of quenched and tempered 4340 UHSS. ..................................................... 25 1-6 The effect of tempering on the flow stress of various steels. .................... 28 1-7 Absolute flow stress vs. plastic strain of SAE 4340 from hysteresis loops of cyclic testing. ........................................................................................ 31 1-8 STF vs. tensile yield stress for different steels including conventional steels and UHSS. ..................................................................................... 35 1-9 ES-1 symmetric plate impact experimental setup of Martin et al. ............. 37 1-10 Tresca yield surface in Haigh-Westergaard space with the hydrostatic axis and deviatoric plane. ......................................................................... 40 1-11 Von Mises yield surface in Haigh-Westergaard space with the longitudinal axis as the hydrostatic axis. ..................................................................... 41 1-12 Projection in the biaxial plane of the yield surfaces of Drucker, Mises, and Tresca yield criteria. ................................................................................. 42 1-13 Cazacu and Barlat yield surface in Haigh-Westergaard space. ............... 44 1-14 Projection in the biaxial plane of the Cazacu and Barlat yield surface corresponding to flow stress ratios of 3/4, 1, and 5/4. .............................. 45 2-1 Z-stack of several pores on the polished surface of cast eglin steel specimen using CDIC. ............................................................................. 52 2-2 Photomontage stitched from nine individual images of the polished surface of cast ES-1 specimen containing several pores. ....................................
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