Recently, a laboratory-scale method for measuring the rapid energy release from milligram quantities of energetic material has been developed based on the high-temperature plasma chemistry induced by a focused, nanosecond laser pulse. The ensuing exothermic chemical reactions result in an increase in the laser-induced shock wave velocity compared to inert materials. Laser-induced air shock from energetic materials (LASEM) provides a method for estimating the detonation performance of novel organic-based energetic materials prior to scale-up and full detonation testing. Here, the extension of LASEM to non-organic energetic materials is discussed. The laser-induced shock velocities from reactive materials such as Al/PTFE, Al/CuO, Al/Zr alloys, Al/aluminum iodate hexahydrate, and porous silicon composites have been measured; in many cases, the high sensitivity of the samples resulted in propagation of the reaction to the surrounding material, producing significantly higher shock velocities than conventional energetic materials. Methods for compensating for this effect will be discussed. Despite this limitation, the relative comparison of the shock velocities, emission spectra, and combustion behavior of each type of material provides some insight into the mechanisms for increasing the energy release of the material on a fast (μs) and/or slow (ms) timescale.

Nanoenergetic composites are of overwhelming interest to the Department of Defense because of the higher power output and the ability to finely tune the ignition thresholds of these composites. Recently, several variants of a nanoaluminum-poly(perfluorinated methacrylate) (AlFA) have been synthesized and optimized for a variety of applications including reactive warhead liners and bullet spotters. While conventional techniques such as thermal analysis and bomb calorimetry can be used to characterize the reaction mechanism and energy output of AlFA composites, characterizing their dynamic behaviour is more challenging. Bullet spotter applications require a material to be impact sensitive at very low velocities, yet be adequately insensitive. Several live-fire tests were conducted which revealed the AlFA50 material reacted consistently upon target impact at high velocities, but unreliably at very low velocities. In an effort to better understand the fundamental impact ignition mechanism and to determine the impact velocity threshold of AlFA50 a series of Taylor gas gun experiments were conducted. It was determined that the light-initiation mechanism was consistent with a pinch mechanism, and that the ignition velocity threshold was near 74 m/s. Based on these results, it was hypothesized that the addition of a filler material could be used to sensitize the AlFA50, and that Asay shear impact testing could be used to determine a more optimal shape of such inclusions. Experiments performed using the Asay shear impact test setup confirmed the pinch ignition mechanism, but observations also revealed that the size of the pinch point was important. Finally, it was shown that the addition of large glass beads (> 1mm in diameter) was effective at sensitizing the AlFA50 material at high and low velocities, with ignition observed at impact velocities as low as 35 m/s.

Rapid or explosive heating of electrically conductive films has several applications, and the use of reactive laminates to increase output energy is an intriguing concept. Past studies have shown electrically heated aluminum/nickel (Al/Ni) nano-laminate films to augment this energy by an amount approximately equivalent to the expected heat of mixing between the two elements, which for most intermetallics is a significant fraction of the total heat of reaction (86% for Al/Ni). In this study, we investigate the use of sputtered aluminum/boron (Al/B) laminates to determine whether a similar increase, as measured by the velocity of an ejected flyer layer, occurs. However, observed velocities in any samples containing boron were 38% to 45% lower than samples without boron, despite much higher heats of reaction reported in the literature for Al/B. We attributed this reduction to the vaporization temperature of boron being much higher than that of Al, and because Al electrical resistivity at elevated temperatures was still much lower than boron, boron heating was less efficient as vaporized Al expanded and drove the ejected flyer. These results and analysis give insight into other reactive material combinations in which one of the constituents is an electrical insulator.

Underwater welding using reactive materials pre-deposited at the junction surfaces as a self-contained, in-situ ignitable heat source mitigates external power and gas supply requirements. Consequently, lending itself to robotic implementation eliminating the cost along with health and safety hazards of human welder-divers. This project reports on lap joining of aluminum sheets with sandwiched commercial reactive Ni-Al multilayers that are perforated to allow for melt fusion under compression upon ignition, in saline and deionized water as well as air for comparison. Finite-element thermal simulations are employed to study the resulting welding temperature field and melt conditions. Infrared pyrometry and thermocouple measurements during welding were used to validate the computational simulations. The lap joints are subjected to standard shear testing, and comparable compliance, strength and toughness values of the welds are assessed for underwater and dry joints. Scanning electron (SEM) of the weld sections reveal rapidly melting and solidifying microstructures of the parent metal, with minimal melt flow and perfusion of nickel aluminide aggregates from the reacted multilayers, and no signs of cavitation.