Submicron plasticity: yield stress, dislocation avalanches, and velocity distribution

TL;DR

This study uses simulations to analyze plastic deformation in submicron crystals, revealing a well-defined yield stress, dislocation avalanche behavior, and universal velocity distribution features related to the jamming-flow transition.

Contribution

It demonstrates the existence of a critical yield stress in micro- and nanocrystals and characterizes dislocation avalanches and velocity distributions during plastic flow.

Findings

Identification of a well-defined critical stress for plastic flow.

Universal cubic decay in dislocation velocity distribution.

Dislocation avalanches cause a shoulder in velocity distribution.

Abstract

The existence of a well defined yield stress, where a macroscopic piece of crystal begins to plastically flow, has been one of the basic observations of materials science. In contrast to macroscopic samples, in micro- and nanocrystals the strain accumulates in distinct, unpredictable bursts, which makes controlled plastic forming rather difficult. Here we study by simulation, in two and three dimensions, plastic deformation of submicron objects under increasing stress. We show that, while the stress-strain relation of individual samples exhibits jumps, its average and mean deviation still specify a well-defined critical stress, which we identify with the jamming-flowing transition. The statistical background of this phenomenon is analyzed through the velocity distribution of short dislocation segments, revealing a universal cubic decay and an appearance of a shoulder due to dislocation avalanches. Our results can help to understand the jamming-flowing transition exhibited by a series of various physical systems.