RUNAWAY REACTION IN A SOLID EXPLOSIVE CONTAINING A SINGLE CRACK

Abstract. The process of a flame entering a narrow slot in the high explosive PBX 9501 is characterized. Pressure traces were used to record the rate of pressurization and streak records are used to track the flame position in the slot versus time. Slots were of width 76.2 µm and two different lengths (4.06 cm and 19.01 cm) were used. In the shorter length slot, the flame either oscillates in and out of the slot or enters the slot in stages, possibly paus-ing to preheat the HE ahead in the unreacted region before proceeding. Maximum pressure values of 150 bar and flame propagation velocities of 60 m/s were measured before reaction was quenched due to depressurization of the test cell. Tests performed with the longer length slot better illustrated the effect of confinement on the reaction. The flame in the long slot accelerated to a velocity of 1500 m/s and the slot was pressurized to 7 kbar before the walls of the test cell failed. It is suspected that this dramatic runaway reaction as due to the rate of gas production from deflagration inside the narrow slot exceeding the rate of gas venting, resulting in rapid pressurization of the slot. This pressurization increased the reaction rate of the burning and decreased the reaction zone length. It is thought that when the pressurization reached a critical value, the reaction was able to access the porosity of the explosive, lead-ing to a runaway reaction. This work is of critical importance in understanding the violent response of HE and rocket motor propellant that has been damaged by mechanical or ther-mal insult. The rapid pressurization and high flame speeds observed can have catastrophic consequences for personnel involved in the operation of systems using the damaged material