A crystal plasticity-based microdamage model and its application on the tensile failure process analysis of 7075 aluminum alloy

In this study, a microdamage model by introducing the damage of crystal is proposed. Damage variables are defined for each slip system, and the damage-coupled crystal plasticity constitutive equations are derived by virtue of the concept of effective stress and the hypothesis of strain equivalence. A function of damage driving force is proposed by analyzing failure mechanisms. The damage evolution equation is then derived based on thermodynamics. After that, a differential evolution-based method is adopted for the calibration of the parameters, and a numerical simulation algorithm is implemented for the failure process simulation of a single crystal material for verification purposes. The proposed model and the corresponding numerical method are then applied to the failure process analysis of a polycrystalline material 7075 aluminum alloy. The EBSD observation is conducted to obtain the size and orientation of grains, which combines with the Voronoi diagram method to be the basis for establishing the polycrystal finite element model. Afterwards, the numerical simulation of the failure process of specimens under tension is conducted. The predicted results are in good agreement with the experimental observations. It indicates that the proposed model can well reflect the damage-softening effect from the microplasticity to the macroscopic deformation. Finally, the two damage mechanisms of grains in 7075 aluminum alloy are investigated based on the calculated result.