High velocity impact-induced initiation and energy release behavior of pre-stressed aluminum reactive materials*

Pre-stressing aluminum (Al) particles by annealing and quenching Al powder alters particle mechanical properties and is linked to an increase in ignition sensitivity under low velocity (0.1-4 m/s) drop weight impact tests. Pre-stressing Al particles alters their reaction mechanism by promoting decohesion and fracture of the alumina shell due to high tensile stresses in the Al core leading to much more pronounced fracture of unsupported shells. This work extends ignition studies of pre-stressed Al powder to high velocity impact ignition. Towards this end, a new laboratory scale high velocity impact system has been developed to examine ignition and combustion behaviors of pre-stressed Al pellets at velocity ranges between 150-1500 m/s. This system is capable of firing a 2 g projectile from a .410 shot gun shell into a catch chamber. The catch chamber is instrumented with pressure transducers. high speed imaging diagnostics to examine impact velocity, fragmentation, and combustion in situ, and UV/VIS spectroscopy to examine combustion timescales. Preliminary results for micron and nanoparticle Al pellets (both prestressed and untreated) with PVDF binder will be presented, along with characteristic images and spectra during impact.