Numerical Prediction of Ductile Damage in Metal Forming Processes Including Thermal Effects

Abstract

The paper is dedicated to the study of the multiphysical coupling in metal forming. Attention is paid to the coupling between thermal exchange, small strain elasticity, finite plasticity with nonlinear hardening, ductile damage, and contact with friction. The standard framework of the thermodynamics of irreversible processes with state variables is used to derive fully coupled thermo-elastoplastic constitutive equations accounting for mixed nonlinear hardening and ductile damage. The related numerical aspects concerning both the local integration scheme of the constitutive equations, as well as the global resolution strategies of the associated Initial and Boundary Value Problem (IBVP) are shortly discussed. For the local integration, an asymptotic iterative scheme is used together with a reduction in the number of the integrated constitutive equations. This model is implemented into ABAQUS/Std using the Umat and Umatht user subroutines. A special care is given to the exact calculation of the consistent stiffness matrix required by the Newton-Raphson implicit resolution strategy of the coupled mechanical and thermal IBVPs. Applications are made to simple examples and the interactions between hardening plasticity, ductile damage, and thermal fields are carefully analyzed.