Yielding of a Model Glassformer: an Interpretation with an Effective System of Icosahedra

TL;DR

This study investigates how shear rates influence shear localization in a model glassformer, linking local structural icosahedra formation to effective temperature changes during deformation.

Contribution

It introduces an interpretation of glassy yielding using an effective system of icosahedra, connecting local structure to shear response and localization behavior.

Findings

Shear localization depends on temperature and shear rate.

Higher effective temperatures correlate with shear localization regions.

Shear induces significant local temperature increases before steady state.

Abstract

We consider the yielding under simple shear of a binary Lennard-Jones glassformer whose super-Arrhenius dynamics are correlated with the formation of icosahedral structures. We recast this glassformer as an effective system of icosahedra [Pinney et al. J. Chem. Phys. 143 244507 (2015)]. Looking at the small-strain region of sheared simulations, we observe that shear rates affect the shear localisation behavior particularly at temperatures below the glass transition as defined with a fit to the Vogel-Fulcher-Tamman equation. At higher temperature, shear localisation starts immediately upon shearing for all shear rates. At lower temperatures, faster shear rates can result in a delayed start in shear localisation; which begins close to the yield stress. Building from a previous work which considered steady-state shear [Pinney et al. J. Chem. Phys. 143 244507 (2016)], we interpret the response to shear and the shear localisation in terms of a \emph{local} effective temperature with our system of icosahedra. We find that the effective temperatures of the regions undergoing shear localisation increase significantly with increasing strain (before reaching a steady state plateau).