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Intermolecular reactive composites find diverse applications in defense, microelectronics and medicine, where strong, localized sources of heat are required. However, fundamental questions of the initiation and propagation mechanisms on the nanoscale remain to be addressed, which is a roadblock to their widespread application. The performance and response of these materials is predominantly influenced by their nanostructure, and the complex interplay of mechanical, thermal, and chemical processes that occur at very short time scales. Motivated by experimental work which has shown that high-energy ball milling (which leads to the formation of granular composites of Ni/Al) can significantly improve the reactivity as well as the ease of ignition of Ni/Al intermetallic composites, we present large scale (~41 million atom) molecular dynamics simulations of the shock response of granular Ni/Al composites, which are designed to mimic the microstructure that is obtained post mechanical milling. The shock response of granular composite materials is not well understood, and much less so for reactive nano-composites. Fully atomistic simulations such as these provide a unique insight into the subgrain response of granular media. Shock propagation in these porous, lamellar materials is observed to be extremely diffuse at low impact velocities, leading to large inhomogeneity in the local stress states of the material; whereas at higher impact velocities, the shock front is observed to be much sharper. We relate this transition in the nature of the shock, to the mechanism of void collapse, with plastic deformation dominant at slow impacts but jetting into the voids dominant at higher impact velocities.

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Shock response of granular Ni/Al nanocomposites

Intermolecular reactive composites find diverse applications in defense, microelectronics and medicine, where strong, localized sources of heat are required. However, fundamental questions of the initiation and propagation mechanisms on the nanoscale remain to be addressed, which is a roadblock to their widespread application. The performance and response of these materials is predominantly influenced by their nanostructure, and the complex interplay of mechanical, thermal, and chemical processes that occur at very short time scales. Motivated by experimental work which has shown that high-energy ball milling (which leads to the formation of granular composites of Ni/Al) can significantly improve the reactivity as well as the ease of ignition of Ni/Al intermetallic composites, we present large scale (~41 million atom) molecular dynamics simulations of the shock response of granular Ni/Al composites, which are designed to mimic the microstructure that is obtained post mechanical milling. The shock response of granular composite materials is not well understood, and much less so for reactive nano-composites. Fully atomistic simulations such as these provide a unique insight into the subgrain response of granular media. Shock propagation in these porous, lamellar materials is observed to be extremely diffuse at low impact velocities, leading to large inhomogeneity in the local stress states of the material; whereas at higher impact velocities, the shock front is observed to be much sharper. We relate this transition in the nature of the shock, to the mechanism of void collapse, with plastic deformation dominant at slow impacts but jetting into the voids dominant at higher impact velocities.