Study of the mixed tensile-shear ductile fracture of impulsively loaded metal plates by developing a phase-field fracture model with stress triaxiality and Lode parameter dependence

How to numerically describe and reveal the mixed tensile-shear fracture in metallic structures subjected to impulsive loadings is still a challenging problem due to the complexity that both fracture initiation and crack formation are strongly affected by the stress states induced by the dynamic impulse loadings. In this paper, an elastic–plastic phase-field model is developed to capture the mixed tensile-shear ductile fracture of impulsively loaded metal plates. Compared with the existing elastic–plastic phase-field fracture model, the stress triaxiality and Lode parameter dependent fracture initiation energy threshold locus and equivalent effective critical energy release rate are introduced to describe the stress state-dependent fracture initiation and crack formation under complex loadings. The damage parameters used in the proposed model can be calibrated with standard test data, and the calibrated model is applied to study the dynamic failure of clamped mild steel plates subjected to impulsive loading. The results show that the predicted dynamic failure of metal plates under different impulse loadings compares well with the experimental results, which verifies the ability of the proposed model to simulate ductile fracture under complex stress states. The competitive mechanism of tensile and shear fracture during the process from partial to complete tearing of the plate is further revealed. It can be concluded that as the damage evolves, the stress state in the material would approach the one with a lower equivalent effective critical energy release rate, which maximizes the energy dissipation through the fracture. This study is meaningful for evaluating and designing metal structures with better dynamic load-carrying capacity.