The army believe the key to making stronger, lighter and more durable weapons is composite materials. Most armaments are still constructed almost entirely of steel as they have been for more than a century, but the Army’s work with composite materials and processes including ceramic matrix and carbon-carbon composites has shown they are not only much lighter than steel but can also withstand excessive heat, something which can cause systems to fail.
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, In one of the early days of testing, composite material were wrapped around the steel tube of a howitzer, like a jacket. During the first test firing, the gun recoiled, but the jacket didn’t.
A gun must also exhibit “stiffening” properties, which is necessary to lessen vibration and ensure targeting accuracy. Some composites are two to three times stiffer than steel. Another factor that needs to be controlled is dynamic strain, meaning the possibility of the material breaking apart. Dynamic strain failure during testing has actually resulted in the muzzle end of the gun shearing off and flying downrange.
Composites also allow tailorability in design, with different composite formulations used for different parts of a gun. In critical areas, stiffer, more expensive composites can be used, whereas in other areas, less expensive and 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.
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, 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. Some of them fired as many as 250 rounds. Tests were a complete success and this technology is sitting on the shelf, ready for use.
Among crew-served weapons, the 81mm mortar tube and baseplate are now being researched for composites integration, with testing getting underway in about another year.
Metal and ceramic composites are being tested to help with excessive overheating in mortar tubes. Composites could also help reduce the weight of mortar tubes, placing less of a burden on the teams that use them. Composites could reduce the entire weapon from 90 pounds down to 50 pounds, with the base plate alone going from 25 to 15 pounds.
Work is also being done to lighten the M109A6/M284 Paladin Cannon bore evacuator, using composite technology similar to that used on the M256 cannon of the Abrams tank. Composites should lighten the M284 Bore Evacuator from 200 to 78 pounds. The new composites should be ready for use in about five years and may also be used for the 155mm howitzer.