Abstract: Starting from the general form of polynomial unified fracture criteria, and then considering the fundamental principles of material fracture, we theoretically derived the unique equation forms for the first threeorder fracture criteria. Employing molecular dynamics (MD) simulations on the two typical metallic glasses, Cu₆₅Zr₃₅ and Ni₆₂Nb₃₈, under three-axis loading, the critical normal and shear stresses on the shear band plane were obtained at the point of shear instability. A comparative analysis between the derived fracture criteria and MD simulation results revealed that the two-order (2-O) fracture criterion exhibits the best agreement with the shear instability of metallic glasses. Furthermore, the validity of the 2-O fracture criterion at compressive stress state was also examined. Through theoretical derivation and MD simulations, this work concludes that the 2-O fracture criterion is the optimal choice within the polynomial range for the unified fracture criterion.

Key words: Unified fracture criterion, Theoretical derivation, Molecular dynamics simulation, Three-axis loading, Metallic glasses