Projectile Impact Ignition Characteristics of Propellants I. Deflagrating Composite Explosive

The results of an investigation of the projectile impact sensitivity of a deflagrating composite explosive are described. The tests consisted in impacting small cylinders of the propellant with flat-ended projectiles of different diameters fired from guns at various velocities, and observing the impact reaction by an open-shutter camera, photocell, post inspection and weighing of the propellant fragments. The critical ( minimum) impact velocity required to produce a sustained reaction in the propellant decreased with increasing projectile diameter. The nature of the reaction depended on the diameter. At small diameters, the induced reaction was always detonation; whereas at the largest diameter the reaction was deflagration, whose intensity increased with increasing impact velocity. A higher critical velocity then again resulted in detonation. A model based on hot spot initiation in which a pressure-dependent effective hot spot concentration determines the rate of buildup of reaction after ignition is postulated to explain the results. Rapid pressure buildup causes detonation; whereas a low buildup rate allows rarefaction loss which results only in deflagration. The critical velocity threshold for inducing the ignition reaction is consistent with the critical energy concept.