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Multi-Scale Characterization of Hyperplasticity and Failure in Dual Phase Steels Subject to Electrohydraulic Forming

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Multi-Scale Characterization of Hyperplasticity and Failure in Dual Phase Steels Subject to Electrohydraulic Forming University of Windsor Scholarship at UWindsor Electronic Theses and Dissertations Theses, Dissertations, and Major Papers 2013 Multi-scale Characterization of Hyperplasticity and Failure in Dual Phase Steels Subject to Electrohydraulic Forming Javad Samei University of Windsor Follow this and additional works at: https://scholar.uwindsor.ca/etd Recommended Citation Samei, Javad, "Multi-scale Characterization of Hyperplasticity and Failure in Dual Phase Steels Subject to Electrohydraulic Forming" (2013). Electronic Theses and Dissertations. 4929. https://scholar.uwindsor.ca/etd/4929 This online database contains the full-text of PhD dissertations and Masters’ theses of University of Windsor students from 1954 forward. These documents are made available for personal study and research purposes only, in accordance with the Canadian Copyright Act and the Creative Commons license—CC BY-NC-ND (Attribution, Non-Commercial, No Derivative Works). Under this license, works must always be attributed to the copyright holder (original author), cannot be used for any commercial purposes, and may not be altered. Any other use would require the permission of the copyright holder. Students may inquire about withdrawing their dissertation and/or thesis from this database. For additional inquiries, please contact the repository administrator via email ([email protected]) or by telephone at 519-253-3000ext. 3208. Multi-scale Characterization of Hyperplasticity and Failure in Dual Phase Steels Subject to Electrohydraulic Forming By Javad Samei A Dissertation Submitted to the Faculty of Graduate Studies through Materials Engineering in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy at the University of Windsor Windsor, Ontario, Canada ©2013 Javad Samei Multi-scale Characterization of Hyperplasticity and Failure in Dual Phase Steels Subject to Electrohydraulic Forming by Javad Samei APPROVED BY: ________________________________________________________ Dr. A.K. Pilkey, External Program Reader Department of Mechanical and Materials Engineering Queen's University, ON, Canada ________________________________________________________ Dr. S. Das, Outside Program Reader Civil & Environmental Engineering __________________________________________________________ Dr. S. Golovashchenko, Industrial Advisor Ford Research and Advanced Engineering, Dearborn, Michigan, USA __________________________________________________________ Dr. D.O. Northwood, Program Reader Mechanical, Automotive, & Materials Engineering ___________________________________________________________ Dr. A. Edrisy, Program Reader Mechanical, Automotive, & Materials Engineering ___________________________________________________________ Dr. V. Stoilov, Co-Advisor Mechanical, Automotive, & Materials Engineering ____________________________________________________________ Dr. D. Green, Co-Advisor Mechanical, Automotive, & Materials Engineering September 6, 2013 Declaration of Co-Authorship and Previous Publication I hereby declare that this thesis incorporates material that is the result of joint research, as follows: This dissertation incorporates the outcome of joint research undertaken in collaboration with Dr. Sergey Golovashchenko, Mr. Amir Hassannejdasl and Mr. Iman Sari Sarraf under the supervision of Prof. Dr. Daniel E. Green. The collaboration is covered in Chapters 6 and 7 of the dissertation. As the industrial partner, Dr. Sergey Golovashchenko contributed the electrohydraulic forming of DP500, DP780, and DP980 steel sheets at Ford Research and Advanced Engineering, Dearborn, MI, USA. Mr. Amir Hassannejdasl provided a description of electrohydraulic forming process in terms of mechanical engineering. Also, Mr. Iman Sari Sarraf collaborated in performing hardness tests on DP500 and DP780 steels. In all cases, the key ideas, primary contributions, experimental designs, data analysis and interpretation, were performed by the author. I am aware of the University of Windsor Senate Policy on Authorship and I certify that I have properly acknowledged the contribution of other researchers to my thesis, and have obtained written permissions from each of the co-authors to include the above materials in my thesis. I certify that, with the above qualification, this thesis, and the research to which it refers, is the product of my own work. This dissertation includes two original papers that have been previously published/submitted for publication in peer reviewed journals and two conference proceedings, as follows: iii Chapter Publication title/full citation Publication status Chapters J. Samei, D.E. Green, S. Golovashchenko, A. Published Hassannejdasl, “Quantitative Microstructural Analysis 6 and 7 of Formability Enhancement in Dual Phase Steels Subject to Electrohydraulic Forming”, Journal of Materials Engineering and Performance, vol. 22(7), 2013, pp. 2080-2088. Chapter 7 J. Samei, D.E. Green, S. Golovashchenko, Quantitative Accepted for Analysis of the Voids in Dual Phase Steel Sheets Formed publication under Quasi-Static Conditions, Materials Science & Technology, Conference & Exhibition, October 27-31, 2013, Montreal, Quebec Canada Chapter 6 I. Sari Sarraf, J. Samei, D.E. Green, S. Golovashchenko, Accepted for “Strain Hardening in Dual Phase Steels Formed into a publication Conical Die Using an Electrohydraulic Forming Process”, Materials Science & Technology, Conference & Exhibition, October 27-31, 2013, Montreal, Quebec Canada Chapter 6 J. Samei, D.E. Green, S. Golovashchenko, “Metallurgical Submitted on Characterization of Hyperplasticity in Dual Phase Aug. 26, 2013 Steels”, Journal of Manufacturing Science and Engineering: ASME. I certify that I have obtained written permissions from the copyright owners to include the above published materials in my dissertation. I certify that the above material describes work completed during my registration as graduate student at the University of Windsor. I declare that, to the best of my knowledge, my dissertation does not infringe upon anyone’s copyright nor violate any proprietary rights and that any ideas, techniques, quotations, or any other material from the work of other people included in my dissertation, published or otherwise, are fully acknowledged in accordance with the iv standard referencing practices. Furthermore, to the extent that I have included copyrighted material that surpasses the bounds of fair dealing within the meaning of the Canada Copyright Act, I certify that I have obtained a written permission from the copyright owners to include such materials in my dissertation. I declare that this is a true copy of my dissertation, including any final revisions, as approved by my dissertation committee and the Graduate Studies office, and that this dissertation has not been submitted for a higher degree to any other University or Institution. v Abstract In this research, three commercial dual phase steel sheets, i.e. DP500, DP780 and DP980, were formed under quasi-static and high strain rate conditions using the Nakazima test and Electrohydraulic Forming (EHF), respectively. In EHF, as a result of a high-voltage electrical discharge between two electrodes in a water chamber, a shock wave was produced which travelled through the water and formed the sheet into the final shape. When a 34° conical die was used in EHF, significant formability improvement, known as hyperplasticity, was achieved in the specimens compared to the specimens formed in the Nakazima test. In this research, hyperplasticity as well as failure in the specimens were characterized at different scales of observation. Quantitative metallography showed relative deformation improvement of around 20% in ferrite and 100% in martensite when formed under EHF. Dislocations in ferrite and deformation twinning in martensite were found to be responsible for the significant improvements of deformation in the constituents under EHF. As a mechanism of failure, voids were found to nucleate in the ferrite/martensite interface due to decohesion. However, under EHF, the significant deformation improvement of martensite enhanced the plastic compatibility between ferrite and martensite. Consequently, the strain gradient across the ferrite/martensite interface, i.e. decohesion, was reduced and nucleation and growth of the interfacial voids was suppressed. Furthermore, quantitative analysis of the voids showed that void growth in the specimens formed under EHF was slower than in the specimens formed in the Nakazima test. The reason was attributed to impact of the sheet against the die that generates significant compressive and shear stresses which act against void growth. Therefore, under EHF, coalescence of the voids to form micro-cracks was postponed to higher levels of strains which resulted in suppression of failure. Fractography of the specimens showed ductile fracture as the dominant type of fracture under both quasi-static and high strain rate forming conditions. In addition, limited quasi-cleavage fracture was observed in DP780 and DP980 specimens. Shear fracture was also observed in the specimens formed under EHF. vi Table of Contents DECLARATION OF CO-AUTHORSHIP AND PREVIOUS PUBLICATION ......................................................... III ABSTRACT ............................................................................................................................................... VI LIST OF TABLES .......................................................................................................................................
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