Nitramine Propellant Crack Tip Ignition and Crack Propagation of a Burning Sample under Rapid Pressurization

Two major tasks performed during the report period of investigation were: 8i) crack tip ignition phenomena under rapid pressurization and (ii) crack propagation in burning solid propellants. Ignition of nitramine composite propellants located at the tip of an inert crack was investigated both experimentally and theoretically. A theoretical model is proposed for the ignition of nitramine composite propellants. Specific features considered in the model include: a) detailed chemical kinetics information for the ignition of nitramine composite propellants, b) two-dimensional (axisymmetric) geometry for the composite propellant, and c) rapid pressurization of the gas phase simulating actual rocket motor ignition conditions. It is found that the time required for the onset of gas evolution of nitramine propellants decreases as the pressurization rate is increased. Under the same operating conditions, nitramine-based composite propellants are harder to ignite than AP-based propellants. Nitramine propellants with HMX fillers are slightly more difficult to ignite than RDX-based propellants due to higher thermal diffusivity and activation energy for decomposition.