Different modes of crack propagation in burning solid propellants

Abstract

The motivation for this research came from the lack of proper understanding of propagation and branching processes in burning solid propellants. These processes are vital in defining safe operating conditions of high energy solid propellants and interpreting important phenomena during the initial phase of deflagration- todetonation transition (DOT). Several experiments have been conducted, and propellant samples have been recovered by rapid pressurization followed by depressurization. For different pressurization rates, four major modes of crack propagation and/or branching are observed. For very low dp/dt, burning occurs without crack propagation. For dp/dt in the order of 1.4 to 15 GPa/s, an existing crack propagates along its initial direction as a single crack (propagation mode). At high pressurization rates of 30 GPa/s or higher, multiple branching in various directions is observed (branched mode); and at intermediate dp/dt, single crack propagation is accompanied by local branching (mixed mode). The amount of surface area generated by mixed or branched modes is substantially higher than that of the single crack propagation mode, and in real motors, could cause sufficiently severe burning in the damaged zone to result in rocket motor failure.