Brittle-to-Ductile Spall Transition in Laser Shocked Aluminum Alloys

We have explored the role material microstructure plays on the spall strength of alloyed aluminum in the high strain rate range of 10$^{6}$ to 10$^{7}$ s$^{-1}$. We performed pump-probe style experiments using the Z-Beamlet Laser at Sandia National Laboratories to drive shocks in thin slabs of recrystallized Al+3 wt. pct. Mg. Velocity interferometry was used to measure the spall strength of the materials, and post-shot target analysis explored the microscopic fracture morphology. Observation of the Al+3 wt. pct. Mg showed evidence of a combination of brittle intergranular and ductile transgranular fracture features. Post-shot target analysis and hydrocode simulations indicate that this mixed mode failure results from spall dynamics occuring on spatial scales on the order of the grain size.