Atomistic study of the impact response of bicontinuous nanoporous gold as a protection medium: Effect of porous-nonporous interface on failure evolution

Abstract

Compared to their non-porous counterparts, metallic foams are known to exhibit improved functionality (e.g., damping capacity) when subjected to high-speed impact loading. Here, we report the results of a molecular dynamics study of bicontinuous nanoporous gold (NPG) subjected to impact loading. Additionally, we investigate the effects of a heterogeneous impact zone on the fate of a witness specimen initially protected by an NPG target. A cube-shaped flyer object (L0= 408.6 Å) composed of full-density f.c.c. gold (FDG) strikes with impact speed Uflyer= 1.0 km s−1 an initially stationary equal-sized NPG target, which subsequently transmits a dispersed shock wave into a protected FDG witness specimen located at the downstream end of the target. The NPG target is stochastic, with porosity ϕ= 0.5 and mean ligament diameter D¯L=64±6 Å. A corresponding simulation for an FDG target serves as a baseline case. As anticipated, the sharp, planar shock imparted by the FDG flyer rapidly becomes highly curved and broadened along the shock direction in the NPG target. Intense plastic and convective flows (ejecta and jetting) lead to spatially heterogeneous mass flow and energy localization, which persist across the entire length of the NPG target studied. Whereas the shock transmitted by the FDG target leaves the witness specimen intact and essentially undamaged, the heterogeneous stress and flow fields imparted by the NPG target results in destruction of the witness. Independent simulations for the same cube-shaped NPG target shocked on the three statistically equivalent {100} target faces reveal modest run-to-run variability in the target and witness responses. The difference in the effects of the NPG and FDG targets on the witness response motivates additional study of the failure evolution inside the witness. It appears from the preliminary results that the porous-nonporous interface might induce a failure pattern that, in some aspects, resembles failure waves observed in brittle solids.