Thermally activated dynamics of annealed glasses near the yielding transition under cyclic shear

TL;DR

This study uses molecular dynamics simulations to explore how thermal effects influence the dynamic heterogeneity and memory effects in glasses subjected to cyclic shear, revealing distinct structural origins of dynamics below and above yield.

Contribution

It introduces a detailed analysis of thermal effects on memory and heterogeneity in glasses under oscillatory shear, extending understanding beyond zero-temperature models.

Findings

Dynamics are independent of sample preparation at small and large strains.

Near the yield point, dynamics differ significantly at finite temperatures.

Structural origins of dynamics differ below and above yield.

Abstract

While experiments and simulations have provided a rich picture of the dynamic heterogeneity in glasses at constant temperature or under steady shear, the dynamics of glasses under oscillatory shear remain comparatively less explored. Recent work has shown that oscillatory shear protocols can embed a ``memory'' into a glass's structure, whereby the material will exhibit dynamics that are encoded by the oscillatory shear protocol applied. However, most of the computational work studying the memory effect has been performed in the zero temperature limit, and the effects of thermalization are poorly characterized. In this work, we use nonequilibrium molecular dynamics simulations to study the dynamics of a model two-dimensional glass former at low, non-zero temperatures under oscillatory shear. While we show that the systems' dynamics are independent of sample preparation for either small or larger strain amplitudes, the dynamics become distinct near the yield point when the deformation is applied at finite temperature. We then characterize the dynamic heterogeneity using two metrics, one derived from the vibrational modes and one that exploits machine learning to identify regions prone to rearrangement. This analysis provides evidence that the dynamics below and above yield emerge from distinct structural origins that may be important for developing improved constitutive models that can predict memory in disordered solids.