Intermittent dislocation density fluctuations in crystal plasticity from a phase-field crystal model

TL;DR

This study uses a phase-field crystal model to analyze how dislocation densities fluctuate intermittently during plastic deformation, revealing power-law behavior and bimodal distributions linked to shear rates.

Contribution

It introduces a stochastic model that captures the statistical properties of dislocation density fluctuations observed in crystal plasticity.

Findings

Dislocation number fluctuations follow a 1/f^2 spectral density at high frequencies.

Bimodal distribution of dislocation densities occurs at low shear rates.

A stochastic reaction kinetics model reproduces the observed fluctuation statistics.

Abstract

Plastic deformation mediated by collective dislocation dynamics is investigated in the two-dimensional phase-field crystal model of sheared single crystals. We find that intermittent fluctuations in the dislocation population number accompany bursts in the plastic strain-rate fluctuations. Dislocation number fluctuations exhibit a power-law spectral density $1/f^2$ at high frequencies $f$. The probability distribution of number fluctuations becomes bimodal at low driving rates corresponding to a scenario where low density of defects alternate at irregular times with high population of defects. We propose a simple stochastic model of dislocation reaction kinetics that is able to capture these statistical properties of the dislocation density fluctuations as a function of shear rate.