This is no ordinary metal. Created by melting steel around hollow metal spheres, composite metal foam is 70% lighter than sheet metal and can absorb 80 times more energy than steel. It is fireproof, radiation-resistant, and even bulletproof.
Researchers at North Carolina State University recently formulated and tested a metal foam so strong that it shatters armor-piercing bullets upon impact, according to a paper recently published in Composite Structures.
The metal foam can stop a bullet at a total thickness of less than an inch, according to lead researcher Afsaneh Rabiei. “Our material is the strongest one yet. There’s nothing like it on the market,” she says.
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The porous material absorbs energy better than sheet metal due to the air bubbles created by the hollow metal spheres embedded in it. When an object moving at high speed—like a bullet—hits it, the air pockets collapse like bubble wrap. This action absorbs the energy of the projectile, rather than transferring the energy through the material to the other side.
“When a bullet hits something, normally it penetrates into it. But since the bullet cannot penetrate our material, it hits it and bounces off. The force that our material applies to the bullet breaks it,” Rabiei says. “In our experiment, we found that the bullet totally shattered.”
See the researchers’ video of the experiment below:
Metal foam has been around for more than a decade, but it has yet to be widely adopted by the commercial sector. Rabiei’s metal foam draws its strength from the uniform size of the bubbles. “If the bubbles are not the same size, the larger ones will buckle first and the material will fail early,” she says. “There are some companies that are making metal foams, but they are mostly looking into a low energy applications.”
The potential applications of Rabiei’s new metal foam, which is stronger and can absorb high levels of energy, range from body armor to space shuttle siding.
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“If tomorrow I can reach out to an investor in car companies and they want to put it in the bumpers of cars I’d be more than happy with that—or if someone from the army wanted to put it in body armor. All of these applications can save lives,” she says.