CMFs, like other foam metals, are made by injecting gas bubbles into molten metal, which then forms a mixture that sets into a matrix. The resulting material retains the strength of the original metal, but is substantially lighter. In comparison to other metal foams, CMFs have five to six times greater strength-to-density ratio and over seven times higher energy absorption, according to Afsaneh Rabiei, professor in the department of mechanical and aerospace engineering at North Carolina State University.
To test CMF strength, Rabiei applied CMFs as the absorber layer between a boron carbide ceramic plate and Kevlar panels. This CMF-based body armor was able to withstand a round from a 7.62-mm x 51-mm battle rifle and a 7.62-mm x 63-mm M2 armor-piercing projectile.
Although existing Department of Justice–standard type IV body armor has comparable strength, CMF-based armor is substantially lighter. This advantage could potentially be extended to a host of defense and civil applications, such as military and law-enforcement vehicles, boat hulls, oil well drilling platforms and structural shock absorbers, to name a few.
However, CMFs can provide more than just strength. Rabiei’s tests have also shown that CMF is effective in shielding against various types of radiation, including X-rays, gamma rays and neutron radiation. CMF also has a high tolerance to heat, withstanding twice as much as ordinary metals. This would make CMF particularly useful in high-temperature environments and in space.
Currently, Rabiei’s team is working on tailoring CMF for armored vehicles to withstand small-arms fire, storage containers for hazardous material and aerostructure applications. Rabiei’s most recent paper on CMFs can be found in Advanced Engineering Materials.
"If others in the research community would like to work together in exploring additional applications, we'd love to talk to them," said Rabiei.
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