Precursors to plastic failure in a numerical simulation of CuZr metallic glass

TL;DR

This study uses molecular dynamics simulations to analyze the microscopic precursors and variability of failure in CuZr metallic glass under shear, revealing early localization patterns and shear band formation mechanisms.

Contribution

It identifies early non-affine displacement localization as a precursor to shear band formation and failure, providing new insights into the microscopic failure process in metallic glasses.

Findings

Failure occurs at consistent external strain but with microscopic variability.

Shear bands form at the edges of non-affine displacement bands.

Shear band thickness relates to available plastic energy.

Abstract

We deform, in pure shear, a thin sample of Cu$_{50}$Zr$_{50}$ metallic glass using a molecular dynamics simulation up to, and including, failure. The experiment is repeated ten times in order to have average values and standard deviations. Although failure occurs at the same value of the externally imposed strain for the ten samples, there is significant sample-to-sample variation in the specific microscopic material behavior. Failure can occur along one, two, or three planes, located at the boundaries of previously formed shear bands. These shear bands form shortly before failure. However, well before their formation and at external strains where plastic deformation just begins to be significant, non-affine displacement organizes itself along localized bands. The shear bands subsequently form at the edges of these non-affine-displacement-bands, and present an alternating rotation-quadrupole structure, as found previously by \c{S}opu et al. (2017) in the case of a notched sample loaded in tension. The thickness of shear bands is roughly determined by the available plastic energy. The onset of shear banding is accompanied by a sharp increase in the rate of change of the rotation angle localization, the strain localization, and the non-affine square displacement.