Effect of yield surface distortion on the failure prediction of Mg alloy sheets

Abstract

Strong initial and induced anisotropies, observed in the deformation of Mg alloys, have restricted their industrial applications. The initial anisotropic behavior is caused by the initial texture of Mg sheets which are fabricated by successive rolling operations. This behavior could be well described by appropriate yield criteria. However, the texture evolution inside the material induces the distortion of the yield surface, which has strong effects on the hardening and damage evolution. Classical isotropic and kinematic hardening could not precisely describe the induced anisotropic hardening. Therefore, distortional hardening, describing the shape alteration of the yield surface, should be considered in modeling the mechanical behaviors of Mg alloy sheets. In this study, a plasticity model fully coupled with isotropic damage for Mg alloys is proposed, and the constitutive equations are formulated within the thermodynamic framework using state variables. The current constitutive model could accurately reproduce the stress–strain evolution under tension, shear and compression for Mg alloy AZ31. In addition, both of the initial anisotropic yield surface and the subsequent distorted yield surface are captured correctly, and the failure under combined loading path is well predicted by the proposed model.