Shear Localization Lengthscale in Metallic Glasses

Ju Li, Ohio State University

The aged-rejuvenation-glue-liquid (ARGL) shear band model has been proposed for bulk metallic glasses (Acta Mater. 54 (2006) 4293), based on small-scale molecular dynamics simulations up to 20,000 atoms and thermomechanical analysis. The model predicts the existence of a critical lengthscale ~10 nm, above which melting occurs in shear-alienated glass. Large-scale molecular dynamics simulations with up to 5 million atoms have directly verified this prediction. When the applied stress exceeds the glue traction (computed separately before), we indeed observe maturation of the shear band embryo into bona fide shear crack, accompanied by melting. In contrast, when the applied stress is below the glue traction, the shear band embryo does not propagate, becomes diffuse, and eventually dies. Thus this all-important quantity, the glue traction (a property of shear-alienated glass), controls the macroscopic yield point of well-aged glass. We further suggest that the degree of chemical alienation ("chemical softening"), rather than free volume, may be the leading physical factor governing glue traction.

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