A study of the static yield stress in a binary Lennard-Jones glass

TL;DR

This paper investigates the static yield stress in a binary Lennard-Jones glass using molecular dynamics simulations, examining effects of aging, shear rate, and temperature, and linking findings to experimental observations of amorphous materials.

Contribution

It provides a detailed analysis of the static yield stress and its dependence on aging, shear rate, and temperature in a model glass, connecting simulation results to experimental behaviors.

Findings

Yield stress exhibits logarithmic dependence on shear rate and aging.

Yield stress decreases with temperature, especially near the mode coupling temperature.

Hysteresis loops indicate soft glassy material behavior.

Abstract

The stress-strain relations and the yield behavior of model glass (a 80:20 binary Lennard-Jones mixture) is studied by means of MD simulations. First, a thorough analysis of the static yield stress is presented via simulations under imposed stress. Furthermore, using steady shear simulations, the effect of physical aging, shear rate and temperature on the stress-strain relation is investigated. In particular, we find that the stress at the yield point (the ``peak''-value of the stress-strain curve) exhibits a logarithmic dependence both on the imposed shear rate and on the ``age'' of the system in qualitative agreement with experiments on amorphous polymers and on metallic glasses. In addition to the very observation of the yield stress which is an important feature seen in experiments on complex systems like pastes, dense colloidal suspensions and foams, further links between our model and soft glassy materials are found. An example are hysteresis loops in the system response to a varying imposed stress. Finally, we measure the static yield stress for our model and study its dependence on temperature. We find that for temperatures far below the mode coupling critical temperature of the model ($Tc = 0.435$), $\sigmay$ decreases slowly upon heating followed by a stronger decrease as $\Tc$ is approached. We discuss the reliability of results on the static yield stress and give a criterion for its validity in terms of the time scales relevant to the problem.