Microstructural damage analysis of AA6061-T6 sheet under different stress states using a crystal plasticity RVE model

Microstructural damage evolution under different stress states plays a critical role in the macroscopic ductile fracture of sheet metals. This study proposes a two-scale numerical framework that links microstructure-informed simulations with macroscopic fracture modeling for an AA6061-T6 aluminum alloy sheet. A crystal plasticity–based representative volume element (CP-RVE) model is developed in DAMASK to simulate deformation under proportional loading paths, including simple shear, uniaxial tension, plane strain tension, and equibiaxial tension. At the macroscale, the modified Mohr–Coulomb (MMC3) ductile fracture criterion is calibrated using experimental fracture data for AA6061-T6 to establish a fracture locus over a wide range of stress states. Microscopic damage accumulation is evaluated using three slip-system-based damage criteria. The results demonstrate that the CP-RVE framework accurately reproduces the macroscopic stress–strain response and plastic anisotropy of the AA6061-T6 sheet, while microscopic analyses reveal pronounced heterogeneity in strain and damage distributions at the macroscopic fracture instant. For example, based on the accumulated shear strain–based damage criterion calibrated using the RVE response under uniaxial tension, approximately 19%, 60%, and 52% of the material points reach the fully damaged state at the macroscopic fracture strain under simple shear, uniaxial tension, and equibiaxial tension, respectively. In contrast, under plane strain tension, none of the material points reach complete damage at the macroscopic fracture instant. Overall, this work highlights the potential of CP-RVE simulations as controlled virtual experiments for investigating microstructural damage evolution and for supporting the calibration of macroscopic phenomenological ductile fracture models, thereby reducing reliance on extensive experiments.