Examination of Steel Specimens Impacted at Hypervelocity
Final rept. 23 Sep 1974-22 Jun 1975
STANFORD RESEARCH INST MENLO PARK CA
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Steel target plates impacted at hypervelocities by small projectiles of various sizes, shapes, and materials were examined metallographically. The purpose was to provide a physical basis for the development of theories that can be used to predict and interpret hypervelocity impact phenomena and to design projectiles that are more effective in producing backface armor fragmentation. The relative importance of projectile momentum and kinetic energy on target damage is discussed. Several observed effects of projectile material on the extent of back surface damage are explained by the relative high pressure shock impedances of projectile and target. The effect of additional momentum delivered to the target when the projectile vaporizes was studied in a single experiment. Postulated blow-off momentum appears to result in a small increase in target damage, but more data are required before conclusions regarding the effect of projectile vaporization can be drawn. Scaling considerations of the MERDCNRL experiments suggest that 1- to 2-kg spheres traveling at 5 kmsec would be required to spall 8-inch-thick steel armor. The mass ejected from the back surface may be 25 times that of the projectile. Differences in front surface damage morphology produced by low shock impedance and equi- or high impedance projectiles are explained by the tendency of equi- or high impedance projectiles to penetrate and low impedance projectiles to reverse their direction during impact. This is thought to change the direction of the maximum shear stresses produced in the targets and cause the observed changes in shear band orientation.