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Jaiveer Singh,Min‑Seong Kim,Joo‑Hee Kang,Shi‑Hoon Choi 대한금속·재료학회 2019 METALS AND MATERIALS International Vol.25 No.3
Mesoscale simulations based on the resolved shear stress (RSS) analysis and the crystal plasticity finite element method(CPFEM) simulations were used to elucidate the deformation behaviors of E-form and AZ31 magnesium (Mg) alloys andthe evolution of tension twin (TTW) and compression twin (CTW) variants during mini-V-bending. RSS analysis, which isbased on the Schmid tensor, was used to calculate the type of twin variants and the number of TTW and CTW variants thatevolved in the deformed Mg alloys. However, RSS analysis considers neither the critical resolved shear stress (CRSS) oftwin systems nor the interaction with neighboring grains, and it failed to accurately predict the twin behaviors of deformedgrains. This study simulated the spatial distributions of the relative activities of different deformation modes, accumulatedtwin fractions, accumulated plastic strains, and effective stresses via CPFEM. Compared with the RSS analysis, CPFEMsimulation precisely explained the twin behaviors observed in both E-form and AZ31 Mg alloys.
Singh, Jaiveer,Kim, Min-Seong,Choi, Shi-Hoon Elsevier 2019 International journal of plasticity Vol.117 No.-
<P><B>Abstract</B></P> <P>Micromechanical deformation behaviors of E-form fine grain (EFG), E-form coarse grain (ECG), and AZ31 magnesium (Mg) alloys were investigated and compared using a mini-V-bending test. EFG and ECG Mg alloys with a weaker texture showed better bendability compared with AZ31 alloy that has a stronger texture. The evolution of the microstructure and microtexture during the mini-V-bending process was experimentally analyzed via an electron back-scattered diffraction (EBSD) technique. This study was focused on the effect that deformation twinning exerts on the strain localization and crack initiation. The twin bands (TBs) developed in the tension zone of bent specimens found to be closely related to the strain localization and crack initiation during the mini-V-bending process. A resolved shear stress (RSS) criterion and microstructure based crystal plasticity finite element method (CPFEM) were used to theoretically predict the activation of { 10 1 ¯ 2 } tension (TTW) and { 10 1 ¯ 1 } compression (CTW) twins in Mg alloys under a mini-V-bending process. RSS analysis indicated that EFG and ECG Mg alloys are more favorable for the activity of TTW and less favorable for the activity of CTW when compared with AZ31 Mg alloy during a mini-V-bending process. However, RSS analysis was not effective in quantitatively predicting twin development. The relative activities of six deformation modes, accumulated twin fractions, and accumulated plastic strains were simulated via microstructure-based CPFEM modeling. Compared with RSS analysis, CPFEM precisely explained the twin behavior that has been experimentally observed in ECG and AZ31 Mg alloys.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The effects of initial texture and grain size in Mg alloys under mini-V-bending tests were investigated. </LI> <LI> The micromechanical deformation behavior was studied using EBSD analysis, RSS criterion, and mesoscale CPFEM modeling. </LI> <LI> Deformation twinning was more prominent in ECG and EFG Mg alloys than in AZ31 Mg alloy during the mini-V-bending. </LI> <LI> In contrast to the RSS criterion, CPFEM modeling more accurately described the twin behavior observed in the experiments. </LI> <LI> The primary deformation mode in ECG and AZ31 Mg alloys was basal '> a and pyramidal '> c + a slip, respectively. </LI> </UL> </P>
Singh, Jaiveer,Kim, Min-Seong,Lee, Seong-Eum,Kim, Eun-Young,Kang, Joo-Hee,Park, Jun-Ho,Kim, Jae-Joong,Choi, Shi-Hoon Elsevier 2018 Materials science & engineering. properties, micro Vol.729 No.-
<P><B>Abstract</B></P> <P>The heterogeneity of both deformation and twinning behaviors through the thickness direction in E-form Mg alloy sheets was investigated via conventional Erichsen testing at room temperature (RT). The microtexture heterogeneity through the thickness direction of the E-form Mg alloy sheets deformed by different punch strokes (PSs) is discussed in terms of deformation twinning and de-twinning. The evolution of the microtexture, twin and KAM (kernel average misorientation) of E-form Mg alloy sheets deformed by different PSs was analyzed via electron back-scattered diffraction (EBSD) technique. A crystal plasticity finite element method (CPFEM) based on a random mapping (RM) scheme was used to simulate the heterogeneities of the strain/stress states of E-form Mg alloy sheets through the thickness direction during an Erichsen test. The evolution of the strain/stress that developed in E-form Mg alloy sheets during Erichsen testing was analyzed for different regions through the thickness direction under different PSs. EBSD analysis revealed that tension (TTWs), compression (CTWs) and double (DTWs) twins were the main deformation mechanisms in the upper portions. However, in the lower portions, a change in the sign of strain/stress components during Erichsen testing resulted in a significant formation of TTWs in the early stages and in a de-twinning of TTWs in the later stages.</P>