Effect of relief hole size on the cook-off characteristics and effectiveness of warhead

The insensitive warhead with a controlled release structural design can significantly reduce the level of response to external stimuli, thereby enhancing the safety of the munition. The pressure relief device is a key component in achieving thermal insensitivity, but the size of its relief holes has opposing effects on the warhead's performance and thermal safety. To maximize warhead effectiveness while ensuring thermal safety, this study combines Fluent and LS-DYNA simulation software to perform numerical simulations of (1 K/min) heating and performance simulation for warheads with different relief hole sizes, exploring the impact of the pressure relief hole cross-sectional area on the baking combustion characteristics of preformed fragment warheads. The numerical simulation results show that the shockwave driving force rapidly increases the velocity of the fragments and casing in the initial loading phase, but its duration is short. In contrast, the expansion force from the detonation gas products, though lower in peak value, exerts a longer-lasting effect. When the explosive driving force and the expansion force from the gas balance the resistance on the fragments, the fragment velocity reaches its maximum, and the stress curve becomes linear. Under the 1 K/min heating rate condition, the cross-sectional area of the relief holes significantly affects the warhead's ignition temperature and ignition time. The ignition response time increases as the relief hole diameter increases, and an optimal relief hole cross-sectional area of approximately 1.2% to 1.4% of the internal charge combustion area results in a higher initial velocity of the fragments.