Heterogeneous shear in hard sphere glasses

TL;DR

This study uses molecular dynamics simulations to demonstrate that in hard sphere glasses, local shear rates correlate with local density fluctuations, revealing heterogeneous flow behavior with consistent fluctuation characteristics across different shear rates.

Contribution

First direct evidence linking local volume-fraction fluctuations to shear rate variations in driven amorphous solids, highlighting heterogeneity in their flow behavior.

Findings

Higher shear rates occur at lower density regions.

Fluctuation time scale is independent of shear rate.

Correlation volume remains roughly constant across shear rates.

Abstract

There is growing evidence that the flow of driven amorphous solids is not homogeneous, even if the macroscopic stress is constant across the system. Via event driven molecular dynamics simulations of a hard sphere glass, we provide the first direct evidence for a correlation between the fluctuations of the local volume-fraction and the fluctuations of the local shear rate. Higher shear rates do preferentially occur at regions of lower density and vice versa. The temporal behavior of fluctuations is governed by a characteristic time scale, which, when measured in units of strain, is independent of shear rate in the investigated range. Interestingly, the correlation volume is also roughly constant for the same range of shear rates. A possible connection between these two observations is discussed.