The shock compression of Reactive Particle Metal Mixtures (RPMMs) is studied at the microscale by direct numerical simulation. Mixture microstructures are rendered explicitly, providing spatial resolution of the coupled thermal, mechanical, and chemical responses at the particle level during shock compression. A polymer-bonded aluminum-iron oxide thermite system is the focus of this work; however, the computational methods developed here may be extended to other reactive particle systems. Shock waves are propagated through the mixtures in finite element simulations, where Eulerian formulations are used to handle the highly-dynamic nature of particulate shock compression. Thermo-mechano-chemical responses are computed for a set of mixture classes (20% and 50% epoxy content by weight) subjected to a range of dynamic loading conditions (particle velocities ranging from 0.300??00 km/s). Two critical sub-problems are addressed: (i) the calculation of Hugoniot data for variable mixture compositions and (ii) the prediction of sites that experience microscale reaction initiation. Hugoniot calculations are in excellent agreement with experimental data. Microscale reaction initiation sites are predicted in certain load cases for each mixture class, although such predictions cannot currently be validated by experimental methods.

The objective of this work is to evaluate the reaction initiation characteristics of quasi-statically compressed intermetallic-forming aluminum-based reactive materials upon impact initiation, consisting of equi-volumetric tantalum-aluminum, tungsten-aluminum, nickel-aluminum, and pure aluminum. A modified Taylor rod-on-anvil setup was employed to determine the reaction initiation threshold kinetic energy and actual energy for plastic deformation and subsequent reaction. Experimental sample remnants were recovered and examined through X-ray diffraction to determine reaction products.The overall results indicate that of the various intermetallic-forming systems investigated, Ta+Al was the most reactive and was the only system where any reaction products were retrieved. While all of the intermetallic systems reacted in air, only Ta+Al and W+Al reacted in vacuum environment suggesting differences in reaction mechanisms influencing the reactivity of intermetallic mixtures. Based on the threshold energy for onset of reaction it appears that the Ta-Al compacts show reaction conditions below those required for reaction of Al in air. This combined with the fact that Ta+Al compacts also react in vacuum implies that the Ta+Al undergoes anaerobic intermetallic reaction while the other systems react with the oxidation of Al. The effect of compact packing density on the kinetic energy threshold for reaction initiation were also evaluated. It was observed more densely packed Ta+Al and Ni+Al powder compacts react more easily than less densely packed samples. While the effect of packing density is not as obvious in the case of pure Al and W+Al powder compacts. Finally, a particle size effect is seen on Ni+Al on samples of < 92% density where coarser (+325 -200 mesh) equal-volumetric powder mixtures were observed to be more reactive than finer Ni+Al (-325 mesh).