A Crystal-Plasticity Cyclic Constitutive Model for the Ratchetting of Polycrystalline Material Considering Dislocation Substructures

A crystal-plasticity cyclic constitutive model of polycrystalline material considering intra-granular heterogeneous dislocation substructures, in terms of three dislocation categories: mobile dislocations, immobile dislocations in the cell interiors and in the cell walls, is proposed based on the existing microscopic and macroscopic experimental results. The multiplication, annihilation, rearrangement and immobilization of dislocations on each slip system are taken as the basic evolutionary mechanism of the three dislocation categories, and the cross-slip of screw dislocations is viewed as the dynamic recovery mechanism at room temperature. The slip resistance associated with the isotropic hardening rule results from the interactions of dislocations on the slip systems. Meanwhile, a modified nonlinear kinematic hardening rule and a rate-dependent flow rule at the slip system level are employed to improve the predictive capability of the model for ratchetting deformation. The predictive ability of the developed model to uniaxial and multiaxial ratchetting in macroscopic scale is verified by comparing with the experimental results of polycrystalline 316L stainless steel. The ratchetting in intra-granular scale which is obviously dependent on the crystallographic orientation and stress levels can be reasonably predicted by the proposed model.