IMPACT FLASH JET INITIATION PHENOMENOLOGY

Impact flash is caused by emission from a jet of shocked material formed through a shock interaction analogous to the process which occurs in a shaped charge. Shaped charge theory predicts that a jet will form when the impact angle between two colliding surfaces is greater than an initiation angle criterion which is a function of material properties and impact velocity. Because the effective impact angle continuously sweeps over a range of values as a spherical particle impacts a flat target, this jet initiation angle criterion is satisfied at some point during the penetration process. A simple model has been developed which predicts the jet initiation from either the target or the particle material. This jet initiation model, (JIM) resolves an apparent discrepancy between previous studies of the dependence of particle and target materials on the flash intensity and provides strong evidence that the impact flash signature is a characteristic of the material in which jet initiation occurs. This model also provides a reasonable explanation for the unusual flash signatures from the impact of carbon particles against gold targets, which show a decrease in flash intensity with increasing impact velocity between 5 and 15 km/s. © 1990.