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

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.