Effect of microstructural length scales on spall behavior of copper

Abstract

A systematic study to quantify the effects of specific microstructural features on the spall behavior of 99.999 pct copper has revealed a strong dependence of the failure processes on length scale. Shock loading experiments with Cu flyer plates at velocities ranging from 300 to 2000 m/s (or impact pressures from 5 to 45 GPa) using a 35-mm single/two-stage light gas gun revealed that single crystals exhibit a higher spallation resistance than fine-grained polycrystals and internally oxidized single crystals. However, in contrast to previously reported results, the fine-grained (ϳ8-m) polycrystalline samples exhibit lower damage resistance than the coarse-grained (50-and 133-m) samples. These observations have been analyzed in the context of the length scale inherent in each of these microstructures, and modeled using an analytical model developed recently.

Shock Hugoniot of single crystal copper

“…One conjecture is that we are observing microstructural differences between the different probe positions since the probe area is sufficiently small. If we average all of the velocity profiles on a given shot, the average velocity profile is consistent with previously reported Cu profiles under similar loading conditions [11,12]. Some of the observed behavior could be attributed to radial edge releases since the probe placement was not chosen to maintain 1D compression for any appreciable duration of time at the probe locations.…”

Characterization of recompressed spall in copper gas gun targets

“…If the tensile stress is sufficiently high, voids can nucleate around particles or defects in the material and grow. Spall and the resulting damage have been studied extensively for shock loading created by gas guns [1][2][3][4] , explosives [5][6][7][8] and laser ablation [9][10][11] .…”

Scaling, Microstructure and Dynamic Fracture

“…Our goal is to understand the role of microstructure in the nucleation and growth process and put it on a more quantitative basis. A self-consistent quantitative theory is introduced that agrees well with a number of experimental observations [1,2]. The centerpiece of the quantitative theory is the size distribution of microvoids either induced or preexisting in the stressed metal.…”

“…The theory presented here was guided by the results from a suite of Cu on Cu gas-gun experiments described in detail elsewhere [1,2]. The controls in the experiments were the Cu impact velocity and the initial microstructure of the Cu target.…”