Experimental Study on the Reaction Evolution in Confined Pressed PBX After Ignited at Different Bulk Temperatures

ABSTRACT Under unexpected thermal stimuli, energetic materials may exhibit a range of non‐shock ignition responses, including ignition, combustion, and, in extreme cases, detonation. To systematically examine the influence of explosive bulk temperature at ignition on reaction evolution, an experimental setup was developed for both laser‐induced forced ignition and high‐temperature spontaneous ignition of confined charges. HMX/NTO‐based pressed PBX specimens were heated to predetermined temperatures, followed by either laser‐induced forced ignition or thermal runaway (analogous to cookoff). Post‐ignition reaction evolution was characterized using multiple diagnostics, including internal pressure sensors, photon Doppler velocimetry (PDV), and free‐field shock wave overpressure measurements. Results show that increasing the bulk temperature accelerates pressure rise within the confinement, enhances free‐field peak overpressure, and increases casing fragmentation severity. Near HMX's polymorphic transformation temperature, pressure buildup duration and pressurization rate change by orders of magnitude. Temperature‐dependent laminar burning rate and thermally induced microstructural damage are identified as the primary factors controlling reaction evolution. Maintaining the charge bulk temperature below HMX's phase transition at ignition can mitigate reaction intensity. These findings provide quantitative insights into the influence of bulk temperature on the reaction intensity of confined energetic materials.