Composite metal foams (CMFs) are little-known materials that are beginning to show some big promise. Last year we saw researchers adapt these lightweight materials to stop various forms of radiation in their tracks, and now the same team has ramped things up to offer protection from something with a bit more force: an armour-piercing bullet, which was turned to dust on impact.

In its most simple form, foam metal is made by bubbling gas through molten metal to form a frothy mixture which then sets as a lightweight matrix. This leaves a material that offers a lighter alternative to conventional metals, while still maintaining a comparable strength.

Afsaneh Rabiei, a professor of mechanical and aerospace engineering at North Carolina State University, last year produced a foam metal shield that could block X-rays, various forms of gamma rays and neutron radiation, giving it potential as a lightweight alternative to the bulky radiation shielding currently available.

Afsaneh Rabiei with one of her composite metal foams

Building on this previous work, Rabiei then set about building high-strength armor. The shield was comprised of boron carbide ceramics as the strike face, with composite metal foam (CMF) as the bullet kinetic energy absorber layer and Kevlar panels as backplates. To test its durability, Rabiei and her team took aim with a 7.62 x 63 mm M2 armor-piercing projectile, which was fired in line with the standard testing procedures established by the National Institute of Justice (NIJ).

"We could stop the bullet at a total thickness of less than an inch, while the indentation on the back was less than 8 mm," Rabiei says. "To put that in context, the NIJ standard allows up to 44 mm (1.73 in) indentation in the back of an armor."

But Rabiei imagines her work will provide more than just ultralight, bullet-destroying body armor. Other potential applications include space exploration and transportation of nuclear waste due to its aforementioned abilities to block radiation.

You can check out the bullet's demise in the video below, while the research was published last year in the journal Composite Structures.

Source: North Carolina State University