The response of a high purity alumina to plate-impact testing

Abstract

Alumina disks which were vacuum hot pressed from a 99.99% pure Al2O3 powder were subjected to flyer‐plate impact testing. VISAR techniques were used to measure rear surface velocities. The Hugoniot elastic limit (HEL) for this alumina was 11.9 GPa. At a precompression of three times the HEL, a remarkably high spall strength of 1.2 GPa was observed. However, a negligible spall strength was found when the alumina was shocked to approximately 1.3 times the HEL. These results indicate that the spall strength of pure polycrystalline alumina goes through a transition, first decreasing in value near the HEL and then increasing again above the HEL. In other flyer‐plate impact tests, manganin stress gauges were used to measure the decay of the HEL with specimen thickness. The HELL for this alumina decreases slightly when the thickness of the specimen was increased but stabilized for specimens thicker than about 9 mm.