Hugoniot and release-adiabat measurements for selected geologic materials

Abstract

Release-adiabat curves have been determined for playa alluvium, tonalite, and novaculite shocked to stresses between 1 and 50 kb by plane impact from a light-gas gun. Particle-velocity/time profiles through the shock compression and the following release were measured at interfaces within the rock target and at the free surface using the principle of a moving conductor in a magnetic field. Steep release-adiabat curves in the stress-volume plane and high rarefaction velocities have been determined for alluvium and tonalite, indicating irreversible compaction. For alluvium, the initial rarefaction velocities are twice the shock velocities, which would cause rapid attenuation of the shock wave propagated in a field experiment. For novaculite, shocked below the Hugoniot elastic limit, the release-adiabat curve lies very close to the Hugoniot. The techniques should be applicable at higher stresses to study such problems as the kinetics of shock-induced phase changes.