Lightweight metal foam blocks blastwave, debris from high-explosive rounds

New research from North Carolina State University and the United States Army’s Aviation Applied Technology Directorate shows that stainless steel composite metal foam (CMF) can block blast pressure and fragmentation at 5,000 feet per second from high explosive incendiary (HEI) rounds that detonate only 18 inches away. “In short, we found that steel-CMF offers much more protection than all other existing armour materials while lowering the weight remarkably,” says Afsaneh Rabiei, senior author of a paper on the work and a professor of mechanical and aerospace engineering at NC State. “We can provide as much protection as existing steel armour at a fraction of the weight – or provide much more protection at the same weight. “Many military vehicles use armour made of rolled homogeneous steel, which weighs three times as much as our steel-CMF,” Rabiei says. “Based on tests like these, we believe we can replace that rolled steel with steel-CMF without sacrificing safety, better blocking not only the fragments but also the blast waves that are responsible for trauma such as major brain injuries. That would reduce vehicle weight significantly, improving fuel mileage and vehicle performance.” For this study, researchers fired a 23×152-millimetre (mm) HEI round — often used in anti-aircraft weapons – into an aluminium strike plate that was 2.3 mm thick. 10-inch by 10-inch steel-CMF plates — either 9.5 mm or 16.75 mm thick – were placed 18 inches from the aluminium strike plate. The researchers assessed that the steel-CMF held up against the wave of blast pressure and against the copper and steel fragments created by the exploding round, as well as aluminium from the strike plate. “Both thicknesses of steel-CMF stopped the blastwave, and the 16.75 mm steel-CMF stopped all of the fragments from 15 mm2 to over 150 mm2 sizes,” Rabiei says. “The 9.5 mm steel-CMF stopped most, but not all, of the fragments. Based on the results, a 10 mm steel-CMF plate would have stopped all of the frag sizes.” The researchers also developed computer models of how the steel-CMF plate would perform. When compared to the experimental results, the model matched very closely. The researchers then used the model to predict how aluminium 5083 armour – a type of armour already on the market that has a similar weight and thickness to the 16.75 mm steel-CMF – would perform against HEI rounds. The model showed that, while aluminium armour of similar weight to the steel-CMF panels would stop all of the frags, the aluminium armour would buckle and allow fragments to penetrate much deeper. This would result in more damage to the panel, transferring large amounts of stress to the soldiers or equipment behind the armour. The steel-CMF, on the other hand, absorbs the energy of the blast wave and flying fragments through local deformation of hollow spheres, leaving the steel-CMF armour under considerably less stress — offering more protection against fragments and blast waves. Next steps include testing the steel-CMF against improvised explosive devices (IEDs) and high-calibre, mounted ballistics. The researchers have already tested the CMF’s performance against hand-held assault weapons, radiation and extreme heat.

EurekAlert, 26 March 2018 ; http://www.eurekalert.org

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