Shear Transformation Zones: State Determined or Protocol Dependent?

TL;DR

This paper investigates whether shear transformation zones (STZs) in amorphous solids are fixed regions or protocol-dependent events, providing evidence that they depend on the loading protocol and cannot be predicted from the unloaded material.

Contribution

The study demonstrates that shear transformation zones are protocol-dependent events, not fixed regions, challenging previous assumptions in amorphous solid plasticity theory.

Findings

Infinitesimal protocol changes cause large shifts in plastic event positions.

Plastic events cannot be predicted from unloaded material analysis.

Shear transformation zones are protocol-dependent rather than fixed regions.

Abstract

The concept of a Shear Transformation Zone (STZ) refers to a region in an amorphous solid that undergoes a plastic event when the material is put under an external mechanical load. An important question that had accompanied the development of the theory of plasticity in amorphous solids for many years now is whether an STZ is a {\em region} existing in the material (which can be predicted by analyzing the unloaded material), or is it an {\em event} that depends on the loading protocol (i.e., the event cannot be predicted without following the protocol itself). In this Letter we present strong evidence that the latter is the case. Infinitesimal changes of protocol result in macroscopically big jumps in the positions of plastic events, meaning that these can never be predicted from considering the unloaded material.