NEGATIVE EQUATION OF STATE AND SPALL CRITERAI

摘要

Several types of solids have been subjected to high, one-dimensional, short-duration strains produced by the planar impact of flat plates accelerated either by electrically exploded metal foils or by an air gun. Time-to spall measurements have been made at room temperature on Plexiglas and aluminum. The critical tensile stress was found to depend on the time duration of the pressure pulse in aluminum but not in Plexiglas. The critical spall threshold in Plexiglas was found to increase with increasing temperature: 1 kilo bar at room temperature, 1.5 kilo bars at 68°C, 2 kilo bars at 100°C. The Huguenot equations of state for Plexiglas have been measured at 68°C and 100°C, and for chopped nylon phenol at room temperature and at 100 C. The free surface velocity in chopped nylon phenol, as well as in Plexiglas at sufficiently high velocity, has been shown to drop off with distance at a much higher rate than predicted by simple hydrodynamic theory. As a result, a critical tensile stress cannot be defined in chopped nylon phenol.