A Crystal Plasticity Cyclic Constitutive Model Based on Dislocation Mechanism for Body-Centered Cubic Axle Steel EA4T

Abstract

Based on micro–macro experimental results from body-centered cubic (BCC) axle steel EA4T, this paper develops a dislocation-based cyclic polycrystalline viscoplastic constitutive model for BCC polycrystalline metals, explicitly addressing non-uniform dislocation substructure alongside its evolution within the crystal plasticity theoretical framework. The model adopts three internal state variables: the density of mobile dislocations, the density of immobile dislocations in cell interiors, and the density of immobile dislocations within cell walls. It comprehensively captures dislocation multiplication, annihilation, rearrangement, and immobilization on various slip systems. To enhance its predictive capability for cyclic deformation of polycrystalline metals, the dislocation-based constitutive model incorporates a rate-dependent flow rule, an improved kinematic hardening law and an explicit scale transition criterion. Simulation results demonstrate the model's capability to predict both the evolution of uniaxial and multiaxial ratcheting strain in BCC polycrystalline metals across various stress levels at the macro scale, as well as the rate dependence of the ratcheting deformation. Furthermore, the model can predict the effects of crystallographic orientation and loading level on single-crystal ratcheting deformation.