Mechanism-aware versus Mechanism-agnostic Modeling of Void-Mediated Failure in Nominally Isotropic Magnesium Alloys

Weakly textured magnesium (Mg) alloys often exhibit nominally isotropic stress–strain behavior with muted tension–compression asymmetry, making an isotropic plasticity assumption appear reasonable. Here, we assess the validity of that assumption for ductile damage governed by void growth and coalescence. The response of a nominally isotropic Mg alloy is represented using three constitutive descriptions: isotropic J2 plasticity, orthotropic HILL plasticity, and a mechanism-based multisurface plasticity formulation. Finite-deformation finite-element simulations are performed on a porous periodic unit cell with fully periodic boundary conditions, subjected to constant macroscopic stress states corresponding to purely tensile loading and combined tension–shear loading. The results show that the damage response depends sensitively on the evolving distribution of deformation mechanisms around the void, which cannot be reproduced by isotropic matrix idealization. Importantly, the analysis suggests a subtle yet important role of these mechanisms, which extends beyond setting the net plastic anisotropy that can affect the predicted ductility.