An internal state variable damage model in crystal plasticity

This paper presents a polycrystalline plasticity theory including damage evolution in FCC materials. The formulation is thermodynamically-based and involves a multiplicative decomposition of the deformation gradient into its elastic, plastic and volumetric components. Plastic deformation at the grain level is assumed to occur by rate-dependent crystallographic slip. As a result of accumulated plastic strain and stress triaxiality, damage evolution leading to volumetric deformation is considered to occur within a single crystal by void nucleation, growth and coalescence. The overall stress–strain response of the polycrystalline material is obtained by Taylor averaging on the stress response of each grain. In the model, damage progression arises naturally from averaging each single crystal’s damage evolution. A parametric study is performed to evaluate the amount of damage and strains at fracture on both single and polycrystals in order to understand crystal orientation effects. For validation purposes, model predictions of uniaxial stress–strain data are compared with experimental results for some aluminum alloys, and the comparison is shown to agree very well.