IMPACT-INDUCED DELAYED DETONATION IN AN ENERGETIC MATERIAL DEBRIS BUBBLE FORMED AT AN AIR-GAP

A planar model of a rocket motor has been developed that allows reacti on in a central bore perforated by a projectile to be viewed with high -speed photography. Earlier work with this model showed that a ''bubbl e'' of propellant debris forms in the air gap between energetic materi al layers (bore region) as a result of projectile penetration of one o f the layers. Ignition of the bubble occurs upon impact with the secon d layer, followed by a reaction ranging from mild burning to delayed d etonation, depending on the width of the air gap, properties of the en ergetic material, and degree of confinement. The present paper present s the results of experimental and hydrocode studies to characterize th e latter (delayed detonation) reaction. Results show that reaction ini tiates in the frontal portion of the bubble wall through mechanical (i mpact) shock. It then propagates backward through the bubble wall towa rds the first layer which then detonates. Detonation of the second lay er occurs sympathetically. The reaction is bounded by a lower velocity limit and confined within a range of air gaps that increases with imp act velocity. The upper-air-gap limit roughly coincides with the maxim um expansion distance for the bubble before breakup, while the lower l imit represents the minimum (threshold) damage level for detonation.