A Plastic Damage Model With Mixed Isotropic–Kinematic Hardening for Low‐Cycle Fatigue in 7020 Aluminum

ABSTRACT The paper at hand presents a new numerical model based on experimental investigations of the low‐cycle fatigue behavior of the high‐strength aluminum alloy EN AW‐7020 T6. The developed plastic damage model is based on J2 plasticity with Charboche‐type mixed kinematic hardening blended with a suitable isotropic hardening. However, a detailed investigation reveals that for EN AW‐7020 T6, the model must be augmented with a damage growth model to accurately describe cyclic fatigue including large plastic strains. Different stress splits are tested, whereby the deviatoric/volumetric split is successful in reproducing the desired degradation in peak stress and stiffness. The model includes a nonlinear activation function to ensure smooth transitions between tension and compression and a damage index for the deviatoric part and for the volumetric part. The plasticity model is calibrated using finite element simulations of a dog‐bone specimen and applied to the cyclic loading of a compact tension specimen.