Shock compression of aluminum single crystals to 70 GPa: Role of crystalline anisotropy

Crystalline anisotropy effects were examined at high stresses by shock compressing Al single crystals along ⟨100⟩, ⟨110⟩, and ⟨111⟩ orientations to peak stresses ranging from 40 to 70 GPa. Laser-interferometry was used to monitor particle velocity histories, including unloading wave profiles. A single, flat-top shock wave followed by a structured release was observed in all the experiments. Shock velocities and longitudinal sound speeds (onset of release) were also determined from the measured particle velocity histories. Within experimental uncertainty (1%–2%), the Hugoniots for the three orientations were indistinguishable, and a single longitudinal stress-density curve was fit to all peak state data. In contrast, the longitudinal sound speeds (and the resulting longitudinal elastic moduli) in the shocked state showed crystal anisotropy effects over the entire stress range examined (up to ∼50% density compression). The measured longitudinal elastic moduli at the highest stress represent more than a fourfold increase from the ambient value and showed continuing anisotropy with compression. The present findings show that Hugoniots may not be the optimal measure of crystalline anisotropy, and even low-anisotropy single crystals, like Al, can manifest significant anisotropy in elastic moduli at large shock compressions.