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A high-velocity impact-ignition testing system was used to study the dynamic response of brittle thermite projectiles impacting an inert steel target at velocities of 850 and 1200 m/s. The projectiles included consolidated aluminum and bismuth trioxide that were launched by a propellant driven gun into a catch chamber equipped with high-speed imaging diagnostics. The projectiles passed through a break-screen at the entrance to the chamber and either fragmented upon penetrating the break-screen or remained intact prior to impacting the steel target. In all cases, the projectiles pulverized upon impact, and a reacting debris cloud spreads through the catch chamber. At lower impact velocities, the fragmented and intact projectiles produced similar flame spreading rates of 217–255 m/s. At higher impact velocities, the intact projectile produced the slowest average flame spreading rate of 179 m/s because debris rebounding was limited by the length of the projectile and the resulting debris field was highly consolidated in the radial direction. In contrast, the fragmented projectile rebounded into a well dispersed debris cloud with the highest, 353 m/s, flame spreading rate. A kinetic energy flux threshold was proposed as a means for describing the shift in observed debris dispersion and flame spreading rates. A reactivity model was developed based on particle burn times using a computational fluid dynamics code that incorporated heat transfer and particle combustion in a multiphase environment to understand how the particle size influenced flame spreading. Results from the model show a trade-off between faster reactivity and increased drag inhibiting movement for smaller particle debris.

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Energetic materials are often processed at high rates of deformation as colloidal slurries and then cured. The slurries are non-Newtonian colloidal solutions that exhibit changes in microstructure with variations in applied flow. This study shows that changes to microstructure due to applied flow affect the reactivity of energetic thin films. Energetic thin films of identical composition and geometry are prepared with different applied shear rates, which produce variations in the film microstructure by segregating smaller particles toward surfaces. Results show that films exhibit significant gains in flame speed with increasing shear rate. The differences in flame speed are linked to variations in microstructure. Specifically, densification of smaller particles near a boundary promote increased flame speeds. However, when particles become segregated, larger particles tend to contribute less to the overall reaction because they burn slowly compared to the smaller particles. When segregated, the larger particles may not be adding chemical energy to the reaction front because propagation is dominated by the more ignition sensitive smaller particles. This study demonstrates explicit changes in reactivity arising from changes in processing conditions that affect microstructure. Controlling applied shear rate introduces a new approach to regulating energetic material reactivity when processed using extrusion-based advanced manufacturing techniques.