Heterogeneous relaxation dynamics in amorphous materials under cyclic loading

TL;DR

This study uses molecular dynamics simulations to explore how amorphous glassy materials respond to cyclic shear, revealing heterogeneous relaxation, particle clustering, and facilitation effects that depend on strain amplitude.

Contribution

It provides detailed insights into the microscopic relaxation mechanisms and dynamic heterogeneity in amorphous materials under cyclic loading, highlighting the role of particle clustering and facilitation.

Findings

Reversible deformation at small strains over many cycles

Intermittent large particle displacements at higher strains

Increased clustering and facilitation with larger strain amplitudes

Abstract

Molecular dynamics simulations are performed to investigate heterogeneous dynamics in amorphous glassy materials under oscillatory shear strain. We consider three-dimensional binary Lennard-Jones mixture well below the glass transition temperature. The structural relaxation and dynamical heterogeneity are quantified by means of the self-overlap order parameter and the dynamic susceptibility. We found that at sufficiently small strain amplitudes, the mean square displacement exhibits a broad sub-diffusive plateau and the system undergoes nearly reversible deformation over about $10^4$ cycles. Upon increasing strain amplitude, the transition to the diffusive regime occurs at shorter time intervals and the relaxation process involves intermittent bursts of large particle displacements. The detailed analysis of particle hopping dynamics and the dynamic susceptibility indicates that mobile particles aggregate into clusters whose sizes increase at larger strain amplitudes. Finally, the correlation between particle mobilities in consecutive time intervals demonstrates that dynamic facilitation becomes increasingly pronounced at larger strain amplitudes.