An improved damage-coupled viscoplastic model for predicting ductile fracture in aluminum alloy at high temperatures

Predicting the ductile fracture in aluminum alloys during hot deformation is important for controlling product quality. To this end, this paper proposes an improved damage-coupled viscoplastic model for predicting the ductile fracture in aluminum alloys at high temperatures. For this model, a dislocation-based viscoplastic model is adopted, and a novel high-temperature damage model is further proposed. The proposed damage model considers the temperature and strain rate effects and also the nonlinear characteristics and stress triaxiality effect of damage evolution. The influence of stress triaxiality is evaluated through notched tensile tests conducted at different temperatures. To describe the actual material degradation, the damage variable is coupled with yield criteria according to continuous damage mechanics. Furthermore, the determination of model parameters based on the results of the uniaxial and notched tensile tests at different temperatures is considered in detail. The proposed constitutive model is applied to analyze damage evolution in a hot tensile process and to predict the fracture occurring during an isothermal bulging test, by employing the user-defined material subroutine VUMAT. The experimental and simulation results showed good agreement, thereby proving the validity of the proposed model for predicting the ductile fracture in aluminum alloys during hot deformation. This study introduces a novel damage model for predicting the ductile fracture in materials, such as aluminum alloys and certain metallic materials, dominated by tensile deformation at high temperatures.