Meso-scale low-cycle fatigue damage of polycrystalline nickel-based alloy by crystal plasticity finite element method

A mesoscopic constitutive model coupled with crystal plasticity (CP) and damage is established in this paper to investigate the plastic deformation and damage-induced degradation of polycrystalline materials under cyclic loading. Taking the nickel-based alloy as a representative material, the rationality and effectiveness of the proposed constitutive model are first verified through a single-element model containing one grain. On this basis, the stress and strain states and damage evolution of polycrystals under cyclic loading are comprehensively investigated. The constitutive parameters in the proposed model are calibrated against experimental results. It is discovered that the strength degradation of polycrystals under cyclic loading can be more precisely described by the CP constitutive model if the damage is taken into account. The simulation results demonstrate that there are significant differences in the initiation and activity degree of the slip systems inside the grains with various orientations, so that inhomogeneous plastic deformation occurs inside the polycrystal, which ultimately leads to the existence of different damage evolution processes in the internal regions of the materials. As an indicator parameter of fatigue damage, the cumulative plastic strain rises with the number of cycles, resulting in an increase of the damage variable.