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.

The general design of a shock tube that was fabricated and used to produce a shock pulse having a relatively long duration (comparable to that produced by a nuclear detonation) is described. This shock tube used the reflected portion of the wave to produce the peak and early history wave pressure acting on the target, and nozzle flow through the rear of the driver tube to control the remainder of the decaying pressure pulse profile. The estimated pressure profile is compared with the profile obtained by a transducer that was located just above the target surface, and they are in general agreement. The general performance of the shock tube is discussed and suggestions made for further improvement of the technique.

An investigation of the projectile impact sensitivities of single, double and triple base propellants is described. The tests were conducted by firing different diameter, flat-ended brass projectiles into small cylinders of the propellant at various velocities and observing the impact reaction by appropriate sensors. It is shown that at large projectile diameters the impact velocity threshold for inducing detonation in the propellants is higher than for inducing burning (sustained ignition); whereas at small diameters the induced reaction is only detonation. These results are similar to those obtained earlier on a deflagratable composite explosive. They support the general validity of a previously postulated model, which was based on the view that the ignition and reaction buildup in an impacted propellant are independent processes.