Triaxiality-dependent asymmetric plasticity model covering a wide range of stress states for magnesium alloy sheets: Modeling shear and near-plane strain anisotropy

The pronounced tension-compression asymmetry and anisotropy are common problems that severely restrict the forming accuracy of magnesium alloy components. An effective solution strategy involves adopting high-precision yield criteria capable of reconstructing material properties to optimize process parameters. In this work, a novel anisotropic-asymmetric yield criterion based on a coupling strategy of polynomial functions and stress triaxiality is proposed. The model delivers high flexibility and accuracy in capturing the anisotropic and strongly asymmetric response of magnesium alloy sheets, as validated on eight widely different virtual material cases. A systematic calibration procedure for determining the material parameters in both the yield stress function and the plastic potential function of the new model is also provided. Finally, the proposed model was applied to the AZ31 and AZ31B magnesium alloy sheets with markedly different yield loci. Compared with the CPB06ex2, Hu2017, and Zhou2023 asymmetric yield criteria, the new model achieves accurate predictions for 15 stress-related sampling points and 12 strain-related sampling points across six stress states, demonstrating comprehensively superior prediction accuracy. More importantly, the new model accurately captures the anisotropic response characteristics of the AZ31 and AZ31B magnesium alloy sheets under shear and near-plane strain stress states, strongly confirming its accuracy and applicability.