On the Thermodynamics of Dynamic Recrystallization for Viscoplasticity at Large Strains

Abstract

During the thermo-mechanical processing of metals, complex microstructure evolution inevitably occur, altering the marcoscopic material properties. The vital microstructure mechanisms include viscoplastic deformation, dynamic recovery (DRV) and dynamic recrystallization (DRX), leading to the hardening and softening of the material. A thermodynamic framework for dynamic recrystallization is proposed covering the state in crystalline materials. Several improvements are presented for an internal state variable (ISV) model to consider the evolution of dislocations dependent on recrystallized volume fractions and derive the constitutive relations for microscopic and macroscopic quantities coupled to viscoplasticity. The relation between microscopic quantities and the macroscopic hardening stress is clarified based on thermodynamic arguments and thermodynamic consistency is derived. On the numerical side a suitable explicit/implicit algorithm is presented and the evolution equations are validated based on experimental data for OFHC copper. During parameter identification the material parameters are determined solving the inverse problem. In numerical examples the constitutive equations are applied to simulations for uniaxial loading and the characteristics of continuous dynamic recrystallization such as strain softening are illustrated.