Porosity evolution at high strain rates: atomistic simulations, dislocation analysis, and constitutive modeling

Mimicking shock compression experiments, our molecular dynamics simulations explore the mechanical response and plasticity effects under uniaxial high strain rate compression (10**7/s to 10**9/s) for Au and Ta single crystals with a collection of spherical nanovoids, with a radius of 3-4 nm, resulting in an initial porosity of {\%}-10{\%}. Dislocation analysis was used to evaluate and quantify the evolution of plasticity. The evolution of dislocations configuration and densities were predicted and successfully compared to an analysis based on Ashby's concept of geometrically-necessary dislocations. The temperature excursion during plastic deformation was used to estimate the mobile dislocation density. The results obtained are compared with a variety of dislocation-based constitutive models. Plastic activity leads to a decrease in porosity until voids disappear completely. Based on the atomistic simulations, a densification regime was observed in all nanoporous samples studied. With these results, a new strain- based porosity model for metals is proposed for simulations at the continuum scale.