Shear-transformation-zone theory of plastic deformation near the glass transition

TL;DR

This paper reformulates the shear-transformation-zone theory for plastic deformation in glasses, incorporating effective disorder temperature and entropy flow, and validates it against experimental rheology of metallic glasses.

Contribution

It introduces a simplified two-variable model of STZ dynamics, linking steady-state and transient behaviors in glass deformation.

Findings

The model accurately predicts transient rheological responses.

Effective temperature governs plastic response dynamics.

Steady-state viscosity parameters predict transient behaviors.

Abstract

The shear-transformation-zone (STZ) theory of plastic deformation in glass-forming materials is reformulated in light of recent progress in understanding the roles played the effective disorder temperature and entropy flow in nonequilibrium situations. A distinction between fast and slow internal state variables reduces the theory to just two coupled equations of motion, one describing the plastic response to applied stresses, and the other the dynamics of the effective temperature. The analysis leading to these equations contains, as a byproduct, a fundamental reinterpretation of the dynamic yield stress in amorphous materials. In order to put all these concepts together in a realistic context, the paper concludes with a reexamination of the experimentally observed rheological behavior of a bulk metallic glass. That reexamination serves as a test of the STZ dynamics, confirming that system parameters obtained from steady-state properties such as the viscosity can be used to predict transient behaviors.