Thermodynamically-consistent constitutive modeling of hardening asymmetry including isotropic ductile damage for Mg alloys

It is well known that the Mg alloys exhibit strong initial anisotropy and hardening asymmetry during plastic flow. These behaviors are mainly caused by their Hexagonal Close-Packed (HCP) lattice structure and the activation of deformation twinning. In this paper, a thermodynamically-consistent plasticity model is proposed to capture the strong anisotropic/asymmetric behavior of Mg alloys with considering the effect of isotropic ductile damage. A detailed calibration method of the proposed model is provided using shear, tension and compression tests along different orientations of the rolled sheets. The material parameters related to initial anisotropy and strength-differential (SD) effect is treated separately from the hardening and damage parameters. The identification procedure is based on minimizing the difference between experimental measurements and FE simulation results over the whole deformation process until final failure. The parametric study of the newly proposed model is conducted to demonstrate its capability in capturing the hardening asymmetry. The predictive capabilities of the proposed model are illustrated through application to two Mg alloys (AZ31B and ZEK100), both the initial tension-compression asymmetry and unusual stress-strain response under monotonic compression are accurately predicted.