A macro-and microscopic model characterizing unstable shear banding in metallic glass

Based on the free-volume theory and fracture mechanics, a macro-and microscopic model was proposed to describe the unstable progressive shear banding in metallic glass. Firstly, a parameter η was advised to characterize the softening effect during shear banding process. It was defined as the percentage of free-volume change. Then, the shear stiffness degradation during shear banding process could be expressed as the function of η. By means of fracture mechanics, the instability of shear banding process could be established quantitatively by the parameter η. Analytical results show that the different settings of machine stiffness and sample dimensions could result in various energy release rates which will also change the shear banding propagation rate. Therefore, the global instability degree of samples could be attributed to different shear banding rates induced by individual energy release rates. Comparison between existing experimental results and analytical calculations yields a good agreement, demonstrating the reliability of the current model. It is anticipated that this work may shed a sight on enriching the in-depth understanding of shear mechanism of metallic glasses.