Investigating the fracture behaviors of bulk metallic glasses under different dynamic loading rates using phase-field model

Bulk metallic glasses (BMGs) attract significant attention because of their superior mechanical properties. They are potential dynamic structural materials that may be applied in military and aerospace fields as energy penetrators. Unfortunately, the structural reliability under dynamic loading cannot be guaranteed at room temperature because of the catastrophic crack initiation and propagation. Thus, it is vital to ascertain the dynamic fracture behaviors of BMGs and their corresponding mechanisms. In this work, the dynamic fracture behaviors of Zr-based BMGs are investigated through the analysis of the mode-I fracture evolution under different high strain rates using the phase-field method. The crack initiation was observed to change from several branches at the notch tip to one branch with the rate increase, while the evolution in metallic glass changed from one stable crack to fragmentation with multiple branches as the rate increased. To investigate crack evolution features, the relationship between crack extension displacement xs and time t was obtained from the simulation results, and the crack velocity was derived through fitting. The changes in fracture behavior with strain rate are attributed to the effects of the strain rate on the crack dynamics and energy dissipation for the crack initiation. Comparison of crack velocities in different fracture modes allowed to determine the critical velocity for the bifurcation. These results can help design new materials for dynamic structures.