Strain-Hardening Behavior of Dual-Phase Steel under Multistress States
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JMEPEG https://doi.org/10.1007/s11665-019-04236-3
Strain-Hardening Behavior of Dual-Phase Steel under Multistress States Yongsheng Xu, Wenjiao Dan, Chuang Ren, and Weigang Zhang (Submitted January 7, 2019; in revised form July 9, 2019) The complexity and nonuniformity of microdeformation in high-strength dual-phase (DP) steels make it difficult to accurately predict the deformation processes in stamping. Here, in situ experiments under three kinds of stress states and a crystal plasticity finite element (CPFE) model were used to predict the strainhardening behavior of DP steel. The microdeformation in various deformation stages was extracted from metallographs captured during in situ experiments to calculate the strain partitioning functions of each phase. Then, the multistress state mechanical behavior of DP steel was calculated based on the CPFE model combined with the strain partitioning functions of ferrite and martensite. The calculation results showed that (1) the CPFE model could accurately describe the load–stroke curves of the three experiments and that (2) the stress state had a significant effect on the strain partition ratio and the initial critical resolved shear stress of the material. In addition, the stress–strain curves of DP800 steel were predicted under six stress states; these curves did not coincide and had obvious deviations. Finally, the activity of the grain slip systems and the dislocation evolution were analyzed and discussed to predict the microdeformation and stress state effects on strain-hardening behavior. Keywords
CPFE, DP steel, in situ experiment, multistress state, strain partitioning
1. Introduction Advanced high-strength steels (AHSSs) are important lightweight industrial materials applied in situations requiring high reliability and low weight. As a typical AHSS, ferrite– martensite dual-phase (DP) steels have been applied in the automotive industry due to their high strength and good ductility (Ref 1-3). However, compared with low-carbon steel sheets, the forming ability of AHSS is poor (Ref 4, 5). The nonuniformity of hardening and deformation between ferrite and martensite during stamping lead to instability in the formability of DP steels. Stamping is an efficient and cost-effective process for producing complex parts in metal sheet forming. However, most formed sheets are in a complex stress state, and the ultimate strain in such sheets is related to the stress state (Ref 6). To predict the formability of sheets under multistress states, Keeler (Ref 7) and Goodwin (Ref 8) performed many experimental studies on the formation of sheets and proposed the forming limit curve (FLC). Borja et al. (Ref 9) noted that the stress state-dependent theoretical model could accurately describe the plasticity and fracture behaviors of DP and complex phase (CP) steels (DP980, CP980 and CP1180). To account for the influence of the stress
Yongsheng Xu, Wenjiao Dan, Chuang Ren, and Weigang Zhang, Department of Engineering Mechanics and Innovation Center for Advanced Ship and Deep-Sea Exploration
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