Connecting strain rate dependence of fcc metals to dislocation avalanche signatures

TL;DR

This paper links strain rate dependence in fcc metals to dislocation avalanche behavior, showing how increasing strain rate alters avalanche size, microstructure, and dislocation storage, with implications for understanding material deformation.

Contribution

It provides a novel mesoscopic explanation of strain rate effects on dislocation avalanches and microstructure evolution based on advanced dislocation dynamics simulations.

Findings

Larger avalanches occur at higher strain rates.

Strain rate increases the power law exponent of avalanche size distribution.

Microstructure becomes more rearranged with shorter dislocation segments.

Abstract

Strain rate sensitivity is a key feature of material deformation, whose importance is growing both because miniaturized components experience higher effective rates and because small scale simulations increasingly probe such conditions. As a dynamical characteristic, strain rate dependence is shown to be intimately connected to dislocation avalanches, which are a fundamental mechanism of dislocation dynamics. Using carefully designed, state of the art dislocation dynamics simulations in the intermediate range strain rate from 5 to 1000, we show that increasing strain rate promotes the activation of a growing number of stronger sites. The dislocation microstructure progressively rearranges into configurations with shorter segments. Dislocation avalanches become larger through the superposition of simultaneous events and because stronger obstacles are required to arrest them. As a result, the avalanche statistics are strongly affected by strain rate, with a reduced power law regime and an increasing power law exponent. Larger avalanches, in turn, lead to an enhanced dislocation storage rate. Contribution from collinear systems to avalanches and cross slip activity decreases, altering the fraction of screw dislocations and the resulting microstructure. These results provide an original mesoscopic picture of rate sensitivity in this strain rate range and offer a mechanistic interpretation of existing observations and findings from experiments and simulations.