Microscopic origin of nonlinear non-affine deformation and stress overshoot in bulk metallic glasses

TL;DR

This paper develops a microscopic theory linking atomic-scale nonaffine deformation to nonlinear stress responses in metallic glasses, successfully explaining stress overshoot phenomena through a simple, physics-based model.

Contribution

It extends the atomic theory of elasticity to nonlinear regimes by coupling with many-body dynamics, providing a microscopic explanation for stress overshoot in metallic glasses.

Findings

The theory accurately reproduces stress-strain curves and overshoot behavior.

It offers an atomic-level interpretation of the competition between elastic instability and viscous dissipation.

The model requires few parameters and aligns well with experimental data.

Abstract

The atomic theory of elasticity of amorphous solids, based on the nonaffine response formalism, is extended into the nonlinear stress-strain regime by coupling with the underlying irreversible many-body dynamics. The latter is implemented in compact analytical form using a qualitative method for the many-body Smoluchowski equation. The resulting nonlinear stress-strain (constitutive) relation is very simple, with few fitting parameters, yet contains all the microscopic physics. The theory is successfully tested against experimental data on metallic glasses, and it is able to reproduce the ubiquitous feature of stress-strain overshoot upon varying temperature and shear rate. A clear atomic-level interpretation is provided for the stress overshoot, in terms of the competition between the elastic instability caused by nonaffine deformation of the glassy cage and the stress buildup due to viscous dissipation.