Characterization and Modeling of Deformation, Springback, and Failure in Advanced High Strength Steels (Ahsss) Jun Hu Clemson University, [email protected]
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Clemson University TigerPrints All Dissertations Dissertations 12-2016 Characterization and Modeling of Deformation, Springback, and Failure in Advanced High Strength Steels (AHSSs) Jun Hu Clemson University, [email protected] Follow this and additional works at: https://tigerprints.clemson.edu/all_dissertations Recommended Citation Hu, Jun, "Characterization and Modeling of Deformation, Springback, and Failure in Advanced High Strength Steels (AHSSs)" (2016). All Dissertations. 1840. https://tigerprints.clemson.edu/all_dissertations/1840 This Dissertation is brought to you for free and open access by the Dissertations at TigerPrints. It has been accepted for inclusion in All Dissertations by an authorized administrator of TigerPrints. For more information, please contact [email protected]. CHARACTERIZATION AND MODELING OF DEFORMATION, SPRINGBACK, AND FAILURE IN ADVANCED HIGH STRENGTH STEELS (AHSSS) A Dissertation Presented to the Graduate School of Clemson University In Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy Automotive Engineering by Jun Hu December 2016 Accepted by: Dr. Fadi Abu-Farha, Committee Chair Dr. Nicole Coutris Dr. Srikanth Pilla Dr. Gang Li i ABSTRACT New generations of advanced high strength steels (AHSSs), expected with tension strength exceeding 1000 MPa, sufficient cold-stamping ductility, and low-alloyed microstructure, are being highly sought for automotive lightweighting applications without compromising on neither performance nor cost standards. From the standpoint of metallurgy, the most straightforward solution is to realize complex microstructures in the new AHSSs with significant fractions of the strongest ferrous phase, martensite, in combination with the most ductile phase, austenite. Nevertheless, the preliminary- developed new AHSSs exhibit unique and complex deformation, failure, and springback characteristics compared with the conventional steel grades, which thereby bring significant challenges to the current manufacturing infrastructure in automotive sector. To thoroughly investigate this uniqueness and complexity, this research work started from a full set of mechanical experimentation on some target AHSSs to comprehensively understand their deformation, springback, and failure. In the selected AHSSs, in particular, a 980 MPa grade quenched and partitioned (QP980) steel, with tri- phase microstructure of retained austenite, martensite, and ferrite, was primarily investigated, since it would be a baseline material of the developing AHSS grades. Another highlight is that, during the entire experimental work, a stereo digital image correlation (DIC) system was widely employed to not only in-situ accurately measure the full-field material deformation and displacement, but also control the loading directions when necessary. i Furthermore, based on the experimental results, a new phenomenological model was proposed to properly characterize not only anisotropy, complex hardening induced by the Bauschinger effect, but also tension-compression asymmetry and the transformation- induced plasticity (TRIP) effect. Then this new model was implemented via user material subroutine in LS-DYNA. Last but not the least, this work eventually wrapped up with a case study of component-level finite element forming and springback predictions compared with the corresponding actual panels, as an implementation and verification of the previous experimentation and modeling. ii DEDICATION To my families, especially my parents and passed away grandfather iii ACKNOWLEDGMENTS First of all, I would like to express all my gratitude to Dr. Fadi Abu-Farha for his wise guidance and continuous patience during my study and research over the past four years. He was always willing to help when my research encountered bottlenecks. It has been a great pleasure to work with him and I believe that I have learned a lot from him that will affect my future career. I also thank my other committee members, Dr. Nicole Coutris, Dr. Srikanth Pilla, and Dr. Gang Li, for their patient and inspiring suggestions during my studying experience in their classes and this dissertation writing. I would particularly take this opportunity to sincerely acknowledge Dr. Lay Knoerr as well as the entire ThyssenKrupp Steel North America group for offering me a great internship opportunity to work in the steel industry in 2015 and 2016. During this internship, I accumulated precious working experience and accepted very professional trainings on many technical software that are extremely helpful to my research work. In addition, I cherished the collaboration experience with Dr. Youngung Jeong, Dr. Nan Zhang, Zeren Xu, Rakan Alturk, and all the other group mates. I also appreciate the technical support from the Clemson University library and Palmetto cluster groups. Furthermore, many thanks to the U.S. Department of Energy for sponsoring my research project, and AK Steel, ThyssenKrupp Steel, General Motors, Fiat-Chrysler Automobiles, and JSOL Corporation for providing the research materials and/or informative support. Last but not the least, I dedicate this dissertation with the deepest love and gratitude to my families, especially my parents and passed away grandfather, for their unwavering support in the past thirty years. iv TABLE OF CONTENTS Chapter Page ABSTRACT ......................................................................................................................... i DEDICATION ................................................................................................................... iii ACKNOWLEDGMENTS ................................................................................................. iv TABLE OF CONTENTS .................................................................................................... v LIST OF TABLES ........................................................................................................... viii LIST OF FIGURES ........................................................................................................... ix CHAPTER 1: INTRODUCTION ....................................................................................... 1 1.1 Overview of AHSSs .................................................................................................. 2 1.1.1 Advantages of AHSSs ........................................................................................ 3 1.1.2 Generations of AHSSs ........................................................................................ 5 1.1.3 Metallurgy of AHSSs ......................................................................................... 7 1.2 Research Motivations .............................................................................................. 13 1.2.1 Challenges Brought by Complex Microstructure ............................................. 14 1.2.2 Research Questions........................................................................................... 16 1.3 Dissertation Overview ............................................................................................. 16 CHAPTER 2: MATERIAL CHARACTERIZATION ..................................................... 17 2.1 Tension Properties ................................................................................................... 18 v 2.1.1 Tension Behavior at Ambient Temperature and Adiabatic Heating ................ 20 2.1.2 Uniaxial Tension Testing between -50 and 300 ºC .......................................... 32 2.2 Equi-biaxial Loading Testing and Results .............................................................. 50 2.2.1 Experimental Setups ......................................................................................... 51 2.2.2 Equi-Biaxial Stress-Strain Curve...................................................................... 52 2.2.3 Equi-Biaxial Yield Stress and Anisotropy ........................................................ 61 2.3 Failure and Forming Limit ...................................................................................... 63 2.3.1 Theoretical FLC Models ................................................................................... 65 2.3.2 Experimental FLC Determination Techniques ................................................. 69 2.3.3 Unexpected Failure Due to Microstructure Inhomogeneity ............................. 86 2.4 Compression and Cyclic Loading Properties .......................................................... 93 2.4.1 Experimental Setups ......................................................................................... 97 2.4.2 Compression Properties of QP980 ................................................................. 100 2.4.3 Cyclic Loading Behavior ................................................................................ 101 2.4.4 Loading-Unloading Behavior ......................................................................... 104 2.4.5 T-C Asymmetry Affected by Multi-Phase Microstructure ............................. 107 2.5 Summary ............................................................................................................... 112 CHAPTER 3: CONSTITUTIVE MODEL ..................................................................... 114 3.1 Yield Criterion and Function................................................................................. 114 vi 3.2 Flow Rule .............................................................................................................. 124 3.3 Hardening