Observing and Modelling Hot Spot Formation in Individual HMX Grains

Microstructure influences the ignition and growth of hot spots in energetic materials (EM) which in turn effects their sensitivity and performance. We aim to better understand the underlying physics behind EM sensitivity by: 1) conducting high-throughput experiments on individual grains of HMX embedded in polymer revealing hot spot locations and temperatures, and 2) comparing experimental results with microstructurally informed, reactive simulations. The experiments employed laser-driven impactors to shock individual HMX grains embedded in polymer and fabricated into arrays. Simultaneous gated, multi-frame imaging and optical pyrometry were used as the primary diagnostics. By combining fast-frame imaging with pyrometry, we can identify regions of preferred hot spot formation with 1 µm resolution, while tracking hot spot temperatures every 2 ns. Single and defective HMX crystals were tested across several polymer and at varying impactor velocities to identify critical pressure thresholds for hot spots. Simulations were conducted using interface-resolved reactive simulations using a sharp-interface Eulerian framework. This new methodology provides the means to evaluate the influence of microstructural energy localization and predict mesoscale behavior of plastic-bonded explosives.