A nonlocal triaxiality and shear dependent continuum damage model for finite strain elastoplasticity

Continuum damage mechanics provides a powerful tool to describe the effects of the growth of micro-voids on the response of ductile materials at the macroscopic scale. Within the framework of thermodynamic and finite strain elasto-plasticity, this paper develops a new damage model considering both stress triaxiality and shear stress ratio, both of which influence the micro-void evolution and the ductile fracture process. To overcome the nonconverging mesh dependency problems in finite element modeling in the region of strain and damage localization, the new damage model is coupled with the nonlocal regularization. The model is implemented using a mixed explicit-implicit algorithm. In addition, the arbitrary Lagrangian-Eulerian (ALE) remeshing strategy is introduced to avoid difficulties caused by excessive element distortion. Two numerical examples are provided: tension of a plate under plane strain and tension and torsion tests on M5 zirconium alloy. The results show elimination of mesh dependency using the combined nonlocal and ALE method. Parametric studies on the characteristic length in the nonlocal formulation and the damage related factors illustrate that all the parameters significantly influence the damage distribution and the material response. The validation studies also indicate that the proposed model has significant potential to represent material response and predict ductile fracture at both low and high triaxialities.