The size effect on the strength and fracture behavior of metallic glasses reported earlier by the authors is further examined in a mode I fracture from extensive molecular dynamics simulation using multimillion atoms and a method for atomic strain. In sharp contrast to the notch-free and notched samples, with small dimensions, in the large samples, shear bands easily initiate at the notch tips and grow into maturity. We identified two critical length scales for nucleating a shear band: the nucleation zone size d of about 1020nm and the shear length ξ that is at least twice as large as d. The shape anisotropy of the critical nucleus described by the two length scales d and ξ may contribute to deformation anisotropy.

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