Avalanches in 2D Dislocation Systems: Plastic Yielding is not Depinning

TL;DR

This study investigates 2D dislocation avalanches under quasistatic loading, revealing that their scale-free behavior differs from depinning models and is characterized by a constant exponent, challenging previous assumptions.

Contribution

It demonstrates that dislocation avalanche dynamics are fundamentally different from elastic manifold depinning, showing a constant power-law exponent across all stresses.

Findings

Avalanche size distribution follows a power-law with exponent τ=1.

Cut-off of avalanches increases exponentially with applied stress.

Avalanche behavior is scale-free at all stress levels.

Abstract

We study the properties of strain bursts (dislocation avalanches) occurring in two-dimensional discrete dislocation dynamics models under quasistatic stress-controlled loading. Contrary to previous suggestions, the avalanche statistics differs fundamentally from predictions obtained for the depinning of elastic manifolds in quenched random media. Instead, we find an exponent \tau =1 of the power-law distribution of slip or released energy, with a cut-off that increases exponentially with the applied stress and diverges with system size at all stresses. These observations demonstrate that the avalanche dynamics of 2D dislocation systems is scale-free at every applied stress and, therefore, can not be envisaged in terms of critical behavior associated with a depinning transition.