Usually, it takes a lot of heavy, cumbersome metal to stop a bullet. Conventional body armor uses heavy steel or ceramic plates inside a kevlar vest to stop the massive kinetic energy of an armor-piercing bullet. But researchers at North Carolina State University’s Department of Mechanical and Aerospace Engineering think they might have found a better option than solid steel.
It’s called Composite Metal Foam, or CMF — a metal structure filled with porous gas bubbles that decrease its density and weight drastically, but keep much of the original metal’s strength. In a study published last year, NC State’s Dr. Afsaneh Rabiei said that CMFs had a lot of potential uses in personal and vehicle armor, but their potential uses go a lot further than that.
Rabiei and her team fashioned an armored plate made out of a composite of materials. The boron carbide ceramic strike face is commonly used in other body armor, but the plate’s core is lightweight CMF foam. In Rabiei’s vest, the boron carbide stops the bullet, but it’s the CMF foam behind it that absorbs the kinetic energy — so much of it, in fact, that the bullet appears to vaporize on impact. Check it out in action below:
The armor in the video is a 7.62x63 millimeter M80 armor-piercing round, a high-powered rifle round designed to punch through body armor. Instead, it basically vaporizes on the outside of the armor, limiting how much the bullet dents the back of the plate.
“We could stop the bullet at a total thickness of less than an inch, while the indentation on the back was less than 8 millimeters,” Rabiei said in a news release. “To put that in context, the NIJ standard allows up to 44 millimeters indentation in the back of an armor.”
However, all that metal has to go somewhere — if the bullet breaks into fragments, those fragments are going to go somewhere, so it’s a concern that the shrapnel could cause injuries after a bullet strike. Still, the solid steel or composite plates (front, back, and smaller side plates) can weigh up to 8 pounds, and lighter options don’t offer the same protection, unless they’re made with CMFs.
CMF’s are also extremely good at blocking out X-rays, gamma rays, and nuclear radiation, so they have a myriad of uses in aerospace engineering as well. Radiation in particular is one of the largest barriers to sending human beings all the way to Mars. They also absorb heat much more slowly than solid metal, and could be used for new heat-shields for spacecraft re-entering the Earth’s atmosphere. Rabiei and her team are continuing to do research on various configurations of metal foams, but see them as a lightweight alternative to many of the metals we use every day.
Correction (4/13/16): In the original version of this article, it credited the University of North Carolina for conducting the research, when, in fact, it was North Carolina State University. The article as been edited to reflect that.