Study and Design of the Mitigation Structure of a Shell PBX Charge under Thermal Stimulation

To study the design method and pressure relief effect of the mitigation structure of a shell under the action of thermal stimulation, a systematic research method of theoretical calculation-simulation-experimental verification of the mitigation structure was established. Taking the shelled PBX charge as the test material, the pressure relief area that can effectively reduce the reaction intensity of the charge is obtained by theoretical calculation. The influence of the pressure relief hole area, distribution mode, and other factors on the pressure relief effect is calculated by simulation. The pressure relief effect of the mitigation structure was verified by the low-melting alloy plug with refined crystal structure for sealing the pressure relief hole and the cook-off test. The research results show that the critical pressure relief area is when the ratio of the area of the pressure relief hole to the surface area of the charge is A_V/S_B = 0.0189. When the number of openings increases to 6, the required pressure relief coefficient decreases to A_V/S_B = 0.0110; When the length/diameter ratio is greater than 5, the opening at one end cannot satisfy the reliable pressure relief of the shell. The designed low-melting-point alloy mitigation structure can form an effective pressure relief channel. With the increase in A_V/S_B from 0.0045 to 0.0180, the reaction intensity of the cook-off bomb is significantly reduced in both fast and slow cook-off, which improves the safety of the charge when subjected to unexpected thermal stimulation.