Metal Foam Stops 0.50 Caliber Bullets as Well as Steel

Researchers have demonstrated that vehicle armor using composite metal foam (CMF) can stop 0.50 caliber balls and armor-piercing rounds as well as conventional steel armor, even though it weighs less than half of conventional steel armor. This discovery means that vehicle designers will be able to develop lighter military vehicles without sacrificing safety, or can increase protection without making the vehicle heavier.

CMF is a foam that consists of hollow metal spheres - made of materials such as stainless steel or titanium - embedded in a metal matrix made of steel, titanium, aluminum or other metal alloys. In this study, the researchers used a steel-steel CMF, which means that both the spheres and the matrix were made of steel.

In this study, the researchers fabricated a hard armor system consisting of a ceramic panel, CMF core and a thin aluminum backing plate. The armor was tested using 0.50 caliber balls and armor-piercing ammunition. The armor was tested with projectiles fired at impact velocities ranging from 500 meters per second to 885 meters per second.

The CMF layer of the armor was able to absorb 72-75% of the kinetic energy of the ball and 68-78% of the kinetic energy of the armor-piercing projectile.

CMF armor is less than half the weight of rolled homogeneous steel armor needed to achieve the same level of protection, and Rabiei, the inventor of CMF, spent several years developing and testing the CMF material. In other words, we were able to significantly reduce weight without sacrificing protection - which benefits vehicle performance and fuel efficiency.

This work shows that CMF can provide significant advantages to vehicle armor, but there is still room for improvement. These findings stem from armor test results produced by simply combining steel-steel CMFs with off-the-shelf ceramic panels, aluminum backing plates and bonded materials. The CMF material was simply optimized by replacing the steel plates in the standard vehicle armor with steel-steel CMF armor. There is more we can do to make it better. For example, we want to optimize the adhesion and thickness of the ceramic, CMF and aluminum layers, which may reduce the total weight and improve the efficiency of the final armor.

In addition to being lightweight, CMFs are also very effective at shielding against X-rays, gamma rays and neutron radiation - and can withstand twice the fire and heat of the ordinary metals they are made of.

In short, CMFs promise to be used in a variety of applications: from space exploration to transporting nuclear waste, explosives and hazardous materials, to military and security applications, and even cars, buses and trains.