Researchers have discovered that composite metal foam offers greater protection than traditional armor steel plate at a third of the weight. The discovery has broad implications for armored vehicles, and could result in stronger, lighter vehicles better able to protect occupants from the impact of kinetic weapons, explosive shockwaves, and fires.
Scientists at North Carolina State University and the US Army’s Aviation Applied Technology Directorate have invented what they call Composite Metal Foam (CMF). “Metal foam” is exactly what you think it is—metal with sponge-like holes in it. This not only makes CMF lighter than normal metal, but it also makes CMF spongy, allowing it to give slightly under impact, soaking up some of the energy of a collision.
In 2016, Seniorhelpline described an early test involving the material and a M2 .30 caliber armor piercing bullet. The bullet, delivering 2,780 foot-pounds of energy against a block of CMF less than one inch thick, shattered on impact. The same bullet was stopped by one half inch of dense armor plate. Here's the video:
CMF is also remarkably good at deflecting blast waves. According to scientists at North Carolina State, the shockwave of an explosion, whether from the direct hit of a tank main gun or an explosive blast, is diffused by with the hollow spheres in the armor. The shockwave, upon encountering the hollow spheres, deforms them and in the process the armor soaks up their energy.
It gets better: CMF is also heat resistant. In tests conducted in 2016, researchers found that it took twice as long for heat to pass through a three quarter inch slab of CMF than it did to pass through a slab of ordinary stainless steel. The Swiss cheese-like holes in CMF create air pockets that slowed heat transmission. In military use, this could slow the spread of heat-caused ammunition explosions, or “cookoffs,” giving crews more time to escape.
But the most fascinating part of CMF is the weight savings. In an article at , Army and university scientists claim that CMF weighs three times less than traditional rolled homogeneous armor (RHA) steel plate used in tanks and armored vehicles. A tank with 12 tons of RHA armor would need just four tons of CMF. Lighter tanks need less powerful engines, increasing fuel economy and decreasing the strain a mechanized unit places on logistics. Alternately a tank could simply carry three times as much CMF than RHA, vastly increasing its armor protection without a weight penalty.
Add on plates of CMF could replace add on panels of reactive armor in offering additional protection to existing armored vehicles. Reactive armor protects armored vehicles by blunting the molten jet of a shaped charge anti-tank round. It is not effective against kinetic energy rounds, such as armor piercing rounds. CMF theoretically offers protection against both.
CMF would be a valuable addition to the Army’s Next Generation Combat Vehicle, which seeks to replace the M1 Abrams main battle tank and M2 Bradley infantry fighting vehicle. The M1 Abrams weighs more than seventy tons, and getting the weight of the Abrams’ successor down without sacrificing armor protection is a top priority.