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The Influence of Deformation-Induced Residual Stresses on the Post-Forming Tensile Stress/Strain Behavior of Dual-Phase Steels

Hance, Brandon Michael (2006) The Influence of Deformation-Induced Residual Stresses on the Post-Forming Tensile Stress/Strain Behavior of Dual-Phase Steels. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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It was hypothesized that, in dual-phase (DP) steels, strain partitioning between ferrite and martensite during deformation results in a distribution of post-deformation residual stresses that, in turn, affects the subsequent strength, work hardening behavior and formability when the strain path is changed. The post-forming deformation-induced residual stress state was expected to depend upon the microstructure, the amount of strain and the prestrain path. The primary objective of this research program was to understand the influence of deformation-induced residual stresses on the post-forming tensile stress/strain behavior of DP steels. Three commercially produced sheet steels were considered in this analysis: 1) a DP steel with approximately 15 vol. % martensite, 2) a conventional high-strength, low-alloy (HSLA) steel, and 3) a conventional, ultra-low-carbon interstitial-free (IF) steel. Samples of each steel were subjected to various prestrain levels in various plane-stress forming modes, including uniaxial tension, plane strain and balanced biaxial stretching.Neutron diffraction experiments confirmed the presence of large post-forming deformation-induced residual stresses in the ferrite phase of the DP steel. The deformation-induced residual stress state varied systematically with the prestrain mode, where the principal residual stress components are proportional to the principal strain components of the prestrain mode, but opposite in sign. For the first time, and by direct experimental correlation, it was shown that deformation-induced residual stresses greatly affect the post-forming tensile stress/strain behavior of DP steels. As previously reported in the literature, the formability (residual tensile ductility) of the IF steel and the HSLA steel was adversely affected by strain path changes. The DP steel presents a formability advantage over the conventional IF and HSLA steels, and is expected to be particularly well suited for complex forming operations that involve abrupt strain path changes.Deformation-induced residual stresses were measured in the IF steel and the HSLA steel; however, the magnitudes of which are such that post-forming tensile stress/strain behavior was not significantly affected. Considering the vast differences in mechanical properties, microstructure, and composition, the IF steel and the HSLA steel showed remarkably similar post-forming tensile stress/strain behavior for all prestrain modes considered.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Hance, Brandon
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairDeArdo, Anthony
Committee CoChairGarcia, C. Isaacgarcia@engr.pitt.eduCIGARCIA
Committee MemberPiehler, Henry
Committee MemberBarnard, John Ajbarnard@engr.pitt.eduJBARNARD
Committee MemberMarangoni, Roy Dmaran@engr.pitt.eduMARAN
Date: 1 February 2006
Date Type: Completion
Defense Date: 22 September 2005
Approval Date: 1 February 2006
Submission Date: 17 November 2005
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Institution: University of Pittsburgh
Schools and Programs: Swanson School of Engineering > Materials Science and Engineering
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: AHSS; DP; ferrite; formability; martensite; neutron diffraction; high strength steel; strain path
Other ID:, etd-11172005-162035
Date Deposited: 10 Nov 2011 20:05
Last Modified: 15 Nov 2016 13:51


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