Composite Metal Foam: Lighter but More Effective Armor


It’s an arms race out there—as more advanced forms of armor are developed to protect soldiers, so do the technologies for weapons that can penetrate these armor. Normally, putting a solid piece of material—usually steel—between yourself and an enemy is the way to go. The thicker, the better, after all, but with one caveat: you make yourself heavier and less mobile. That was true then since the dawn of warfare as it is now.

A research team from the North Carolina State University, however, wants to change that paradigm. In a paper called “Ballistic Performance of Composite Metal Foam against Large Caliber Threats,” they demonstrated a material called composite metal foam (CMF) that can stop a .50-caliber bullet with only less than half the weight of steel armor needed to stop the same projectile. While the widespread metal fabrication of CMF in Utah is still a few years away, these tests mean that ponderous armored vehicles will soon become a thing of the past.

An Impressive Stopping Force

A .50-caliber round, which travels at over 800 meters per second, is the kind of ammunition fired by a sniper rifle or a heavy machine gun. While a .50-cal round will not penetrate any armored vehicle, it’s lethal for infantry in the field, and hitherto the only way to protect them is to outfit them with personal heavy armor. Coupled with their gear, the average American soldier lugs around a weight of 60 pounds (27.2 kilograms).

In the paper, the NCSU lead researcher and materials scientist, Afsaneh Rabiei, simulated how their patented CMF armor fares against a .50-caliber round (also called a 12.7×99 NATO, thanks to its dimensions). In the experiment, the researchers fired normal and armor-piercing bullets at a CMF armor, ranging from 500 to almost 900 meters per second. The results showed that CMF, which formed the core of a ceramic front plate and a thin aluminum back plate, effectively dispersed the energy of the round. The ceramic plate did show cracks, but the CMF core itself is mostly undamaged; it absorbed up to 75% of the force of the regular ball rounds and up to 78% of that of the armor-piercing.

A History of Success

It’s not the first time CMF has been used, however. In fact, Rabiei also helped in the development of CMF 15 years ago in NCSU, and during that time, they tested CMF for other applications. These applications included heat shields and protection against explosives and radiation. For example, her previous tests showed that it can resist the blast of a high-explosive incendiary round as close as 18 inches away and that it can also resist X- and gamma rays.

This test shows great promise for mass adoption in the military. Previously, a smaller round (7.62×63 mm M2 armor-piercing) was tested against CMF, but it only made an indentation in the back plate of only 8 millimeters. This was a new record, as the standard for armor was a maximum indentation of 44 millimeters in the back plate.

Rabiei, however, admitted that CMF can still be optimized for better force absorption, such as thinner front and back plates. This would make the vehicle (or the soldier) using CMF armor lighter and much more mobile without sacrificing protection.

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