Effect of twinning on the yield surface shape of Mg alloy plates under in-plane biaxial loading

The EVPSC-TDT model is first employed to investigate the yield behavior of a strongly basal textured Mg alloy plate under biaxial loading. The material parameters are calibrated according to experimental uniaxial tension and compression along the rolling and plate normal directions. The EVPSC-TDT model with the calibrated parameters is then employed to conduct various biaxial loadings under plane stress condition. The predicted yield surface and its evolution match well with the experimental data. The shape change of the yield surfaces in all four quadrants is interpreted according to the activated deformation modes. Compressive twinning weakens the work hardening behavior in the first quadrant of the yield surface at relatively large plastic strain level, while tensile twinning plays an important role in determining the shape of the second, third and fourth quadrants of the yield surface. A turning point corresponding to pure shear loading is observed in the second quadrant of the yield surface which is caused by the transition of activated deformation modes from basal slip and tensile twinning to non-basal slip. In addition, the effect of initial texture on the shape of the yield surface of Mg alloy plates has been briefly investigated.