A crystal plasticity model of low cycle fatigue damage considering dislocation density, stress triaxiality and Lode parameter

Abstract

To capture the mechanical behavior and low cycle fatigue damage of metals, a crystal plasticity model combined with isotropic continuum damage mechanics model of low cycle fatigue is developed. In this constitutive model, the Lemaitre model of low cycle fatigue damage is modified accounting for the effect of stress triaxiality and Lode parameter, the slip strength is associated with the evolution of the density of statistically stored forest dislocations and debris dislocations, and a non-linear kinematic hardening rule is employed to capture the cyclic response. Simulation is implemented by applying this developed constitutive model to the Voronoi polycrystalline aggregation of 7075 aluminum alloy. The studied results show that the grains with low Schmid factor generally suffer more severe damage compared to those with high Schmid factor. In addition, due to the orientation mismatch of adjacent grains, localized stress concentrations and the resulting severe damage generate near the grain boundaries, especially near the grain boundaries with high misorientation angles. The proposed constitutive model manifests the capacity for the determination of damage evolution of the polycrystalline metals.