Failure criterion for metallic glasses

Metallic glasses exhibit not only multiple failure modes but also differences in ultimate strength, plastic strain to fracture and asymmetric deviation of failure angles from 45 degrees between tension and compression. The available failure theories cannot fully characterize these phenomena and the underlying physics has not been completely clarified. Here, based on the short-range order structure in metallic glasses, we derive an inherent law that determines when metallic glasses might yield or fracture. A unified failure criterion is constructed which satisfactorily predicts the complex failure behavior observed in metallic glasses. We show that the shear-to-normal strength ratio alpha and the strength-differential factor beta, characterizing shearing resistance between atomic layers and shear-caused dilatation, respectively, have dual control over whether metallic glasses yield in a ductile manner or fracture in brittleness.