Partitioning of energy in hypervelocity impact against loose sand targets


  • David Braslau


Aluminum spheres were fired vertically into dry quartz sand in the light-gas gun facility at the NASA Ames Research Center. A velocity of 6.37 km/sec and a chamber pressure of 150 μ were used for all shots. Using an estimated impact pressure of 500 kb, heating of the target was computed to be 26% of the initial projectile kinetic energy, while ejecta absorbed 53%, both figures being very similar to those found earlier for basalt. Energy lost to compaction was 20% of the total initial energy, whereas in basalt it is negligible. Comminution in the already granular sand used about 8% of the energy, whereas for basalt this ranges from 10 to 24%. No observed ejecta velocities exceeded that of the impacting projectile. Most of the fused material, if any, was ejected, and there was an increase in density at the bottom of the crater due to compaction. The final shape of craters in sand emphasizes the importance of target strength at low stress levels.