New Lightweight Metal Foam Destroys Bullets on Impact (video)

A composite metal foam (CMF) has been developed at North Carolina State University that is strong enough to resist bullets, disintegrating them on impact.

The foam is largely composed of steel, but it is much lighter than steel plating. It looks something like a metal sponge.

CMF has been created in the lab using several methods. Basically, a gas of some sort is introduced into the material to create the bubble spaces in it. This can most readily be achieved by directly injecting a gas into the molten, melted, material.

Other methods include using pressurized hydrogen or adding blowing agents which evaporate at a lower temperature so they off-gas in the liquid metal.

The end result is an incredibly strong metallic structure that is both lightweight and low density.

A one-inch thick plate of the material can shred a bullet, leaving an indentation in the back of less than 8 millimeters, reported NC mechanical and aerospace engineering professor Afsaneh Rabiei. By way of comparison, the NIJ standard that currently controls military security plating allows for up to 44 millimeters of indentation.

As an added bonus, CMF has proven to be excellent at blocking X-rays, gamma rays, and neutron radiation, making it a good candidate for transporting nuclear waste, building spacecraft and nuclear structures, and even providing safe shielding for CT scans.

The metal foam is nearly twice as effective at blocking heat, as compared to solid metal, as the bubble spaces act as insulators. The heat does not conduct well through the bubbles, so it is forced to curve through the metal around the shape of the spaces, making it travel further to get through the material.

The bubbles also act as a shock absorber, enabling the metal to compress and absorb the impact in the case of a collision.

While the foam is still in the developmental stage, it could soon change the way we are protected as drivers, astronauts, or soldiers.

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Abstract from Ballistic performance of composite metal foams

Matias Garcia-Avilaa, Marc Portanovab, Afsaneh Rabieia, ,

The application of advance materials to manufacture hard armor systems has led to high performance ballistic protection. Due to its light-weight and high impact energy absorption capabilities, composite metal foams have shown good potential for applications as ballistic armor. A high-performance light-weight composite armor system has been manufactured using boron carbide ceramics as the strike face, composite metal foam processed by powder metallurgy technique as a bullet kinetic energy absorber interlayer, and aluminum 7075 or Kevlar™ panels as backplates with a total armor thickness less than 25 mm. The ballistic tolerance of this novel composite armor system has been evaluated against the 7.62 × 51 mm M80 and 7.62 × 63 mm M2 armor piercing projectiles according to U.S. National Institute of Justice (NIJ) standard 0101.06. The results showed that composite metal foams absorbed approximately 60–70% of the total kinetic energy of the projectile effectively and stopped both types of projectiles with less depth of penetration and backplate deformation than that specified in the NIJ 0101.06 standard guidelines. Finite element analysis was performed using Abaqus/Explicit to study the failure mechanisms and energy absorption of the armor system. The results showed close agreement between experimental and analytical results. http://www.sciencedirect.com/science/article/pii/S0263822315000434