An instability index of shear band for plasticity in metallic glasses

Catastrophic failure along a dominant shear band sets the limit on how much plasticity can be achieved in metallic glasses (MGs) under uniaxial compression. Here we show that this instability process is governed by a single system parameter, called the shear-band instability index (SBI), which is proportional to sample size and inversely proportional to machine stiffness. We provide extensive experimental proof of this concept by conducting a series of tests with a range of controlled values of sample size and machine stiffness. The theory of SBI has led us to a more comprehensive understanding of the mechanisms of plastic deformation in MGs via simultaneous operation of multiple shear bands versus a single dominant one. This concept provides a theoretical basis to design systems which promote plasticity/ductility in MGs by suppressing or delaying shear-band instability.