Damage and Fracture Analysis under Multi-axial Stress State Based on Damage Mechanics

Abstract

In various press forming and deep drawing processes, it is important to anticipate the forming limit in multi-axial stress state. In the uniaxial tension test, it is necessary to take stress triaxiality into account for accurate prediction of failure strain, because after the onset of the necking, the constricted portion, which is actually subjected to loading, is in the multiaxial stress state due to the change in local cross-sectional area. Recently, several damage and fracture models have been proposed that focus on the effect of stress triaxiality on the forming limit, while most of them are phenomenological models. In this study, the constitutive equation and damage evolution equation, which are based on a second-order symmetric damage tensor within the framework of the continuum damage mechanics, are constructed as a function of the stress triaxiality to analyze damage and fracture of materials in multiaxial stress state. Then, FEM analysis of an example problem was carried out to validate this material model.