Glass Dynamics at High Strain Rates

TL;DR

This paper uses shear-transformation-zone (STZ) theory to analyze molecular-dynamics simulations of rapidly sheared metallic glasses across various temperatures, highlighting the role of effective-temperature thermodynamics at high strain rates.

Contribution

The study extends STZ theory to high strain rate metallic glasses and introduces a multi-species generalization to address discrepancies near the glass transition.

Findings

STZ theory reproduces simulation data with a scaling collapse.

High strain rate behavior is governed mainly by effective-temperature thermodynamics.

Discrepancies at lower strain rates near the glass transition can be addressed with multi-species STZ theory.

Abstract

We present a shear-transformation-zone (STZ) theoretical analysis of molecular-dynamics simulations of a rapidly sheared metallic glass. These simulations are especially revealing because, although they are limited to high strain rates, they span temperatures ranging from well below to well above the glass transition. With one important discrepancy, the STZ theory reproduces the simulation data, including the way in which those data can be made to collapse onto simple curves by a scaling transformation. The STZ analysis implies that the system's behavior at high strain rates is controlled primarily by effective-temperature thermodynamics, as opposed to system-specific details of the molecular interactions. The discrepancy between theory and simulations occurs at the lower strain rates for temperatures near the glass transition. We argue that this discrepancy can be resolved by the same multi-species generalization of STZ theory that has been proposed recently for understanding frequency-dependent viscoelastic responses, Stokes-Einstein violations, and stretched-exponential relaxation in equilibrated glassy materials.