Time-temperature superposition for cavitation resistance of metals with nonequilibrium vacancy concentrations

S Adibi and JW Wilkerson, EXTREME MECHANICS LETTERS, 47, 101350 (2021).

DOI: 10.1016/j.eml.2021.101350

Here, we provide a systematic molecular dynamics (MD) study of the pulse duration and temperature dependence of spall strength in Al and Mg with a nonequilibrium concentration of vacancies. A superconcentration of single vacancies are randomly introduced into an otherwise perfect lattice, and the systems are allowed to evolve for up to 500 nanoseconds as a proxy for the pulse duration of a shock compression wave. Since these systems are nonequilibrium in nature, a time-dependent and temperature-dependent evolution of the microstructure ensues, which leads to a time- and temperature-dependent softening of the spall strength. Here, we report a large parametric study consisting of 196 MD calculations to quantify this softening in Al and Mg. We invoke the notion of time-temperature superposition from the field of viscoelasticity, and show that the results of our 196 MD calculations remarkably collapse onto a single master curve when normalized by an appropriate relaxation timescale. Lastly, a favorable agreement between the MD calculations and experimental measurements of thermal softening of spall strength is reported. (c) 2021 Elsevier Ltd. All rights reserved.

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