Hypervelocity impact experiments in surrogate materials

A requirement to perform experiments for hypervelocity impacts in substitute materials arises from the need for data at velocity ranges inaccessible in the laboratory. The role of melt and vapor in hypervelocity shielding designs cannot be assessed with the maximum velocity of approximately 8 km/sec that is achievable. As a consequence, there is interest in performing experiments in materials where the melt and vapor regimes occur at lower velocities.

Such surrogate experiments can in principle be exact. A process in a surrogate material will be dynamically similar at one in the material of interest if the constitutive equations are the same to within three arbitray scale factors given by the ratios of the natural mass densities, sound speeds and viscosities. The experiments can ben performed at scaled size, velocity and time .

Cadmium and zinc are considered as candidates to substitute for aluminum to allow velocity scaling. Their thermodynamic equations of state are constructed from existing data and the ANEOS analytical equation of state model. They are recast in a scaled form in which the satisfaction of the scalign requiremens can be assessed. Reasonable matching is attained. Testing in cadmium at a velocity of 6 km/sec is approximately dynamically similar to experiments in aluminum at 18.6 km/sec, a velocity factor of 3.1.