Strain rate dependency of dislocation plasticity

HD Fan and QY Wang and JA El-Awady and D Raabe and M Zaiser, NATURE COMMUNICATIONS, 12, 1845 (2021).

DOI: 10.1038/s41467-021-21939-1

Dislocation glide is a general deformation mode, governing the strength of metals. Via discrete dislocation dynamics and molecular dynamics simulations, we investigate the strain rate and dislocation density dependence of the strength of bulk copper and aluminum single crystals. An analytical relationship between material strength, dislocation density, strain rate and dislocation mobility is proposed, which agrees well with current simulations and published experiments. Results show that material strength displays a decreasing regime (strain rate hardening) and then increasing regime (classical forest hardening) as the dislocation density increases. Accordingly, the strength displays universally, as the strain rate increases, a strain rate-independent regime followed by a strain rate hardening regime. All results are captured by a single scaling function, which relates the scaled strength to a coupling parameter between dislocation density and strain rate. Such coupling parameter also controls the localization of plasticity, fluctuations of dislocation flow and distribution of dislocation velocity. The relationship between the strain rate and micro-scale deformation in metals is still poorly understood. Here the authors use discrete dislocation dynamics and molecular dynamics to establish a universal relationship between material strength, dislocation density, strain rate and dislocation mobility in fcc metals.

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