The Army is on the cusp of revolutionizing materials that go into armament construction, making for stronger, lighter and more durable weapons. The key to this revolution is composite materials.
Dr. Andrew Littlefield, a mechanical engineer at the U.S. Army Armament Research, Development and Engineering Center at Picatinny Arsenal, New Jersey, presented “Lightweighting of Large Caliber Weapons – Present and Future,” during the National Defense Industrial Association-sponsored 2015 Armament Systems Forum on April 21.
Most armaments are still constructed almost entirely of steel, as they have been for more than a century, he said. The Army’s work with composite materials includes metal matrix, ceramic matrix and carbon-carbon composites in addition to polymer matrix. The heat resistance of composites has real applicability to Army weapons systems because excessive heat is what often causes those systems to fail. Besides the ability of some composites to withstand a lot of heat, another advantage is that they’re much lighter than steel.
One of the biggest problems with composites is getting them to stick to the portions of a gun that must continue to be manufactured of steel, such as the barrel, Littlefield said. In one of the early days of testing, composite material was wrapped around the steel tube of a howitzer, like a jacket. During the first test firing, “the gun recoiled, but the jacket didn’t,” he said.
The XM360 120mm cannon, part of the now-cancelled Future Combat Systems, remains one of the most mature examples of composites development. To ensure that the composite jacket fits securely over the barrel of the XM360, the steel core was first contracted by chilling it with frozen carbon dioxide, Littlefield said. Then, thermal plastic was wrapped tightly around it. Finally, as the frozen barrel warmed up, it expanded into the composite jacket. Fourteen barrels were produced in this manner and each was tested. Tests were a complete success, he said, and this “technology is sitting on the shelf, ready for use.”
Composites also allow “tailorability” in design, Littlefield said. Different composite formulations can be used for different parts of a gun. In critical areas, stiffer, more expensive composites can be used. In other areas, less expensive, more flexible composites can be used. For instance, certain layerings of composites can induce a desirable effect known as “coupling/extension-twist coupling.” This design has been successfully used on experimental helicopters to change the rotors’ attack angle during flight. These composites would allow portions of a gun to twist slightly during recoil, like a rubber band, so the parts don’t shear or crack.
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