Mechanical excitation and marginal triggering during avalanches in sheared amorphous solids

TL;DR

This study compares plastic strain avalanches in amorphous solids using molecular dynamics and elasto-plastic models, revealing how mechanical excitation influences spatial correlations and avalanche size distributions.

Contribution

It demonstrates that simple elasto-plastic models effectively replicate avalanche size distributions by capturing key spatial correlation features observed in molecular dynamics.

Findings

Spatial correlations grow as t^{3/4} in MD and ballistically in EPM.

A longer diffusive lengthscale is associated with remote marginally stable sites.

EPMs accurately reproduce avalanche size distributions despite differences in dynamics.

Abstract

We study plastic strain during individual avalanches in overdamped particle-scale molecular dynamics (MD) and meso-scale elasto-plastic models (EPM) for amorphous solids sheared in the athermal quasi-static limit. We show that the spatial correlations in plastic activity exhibit a short lengthscale that grows as $t^{3/4}$ in MD and ballistically in EPM, and is generated by mechanical excitation of nearby sites not necessarily close to their stability thresholds, and a longer lengthscale that grows diffusively for both models and is associated with remote marginally stable sites. These similarities in spatial correlations explain why simple EPMs accurately capture the size distribution of avalanches observed in MD, though the temporal profiles and dynamical critical exponents are quite different.