NC State Professor Creates Lightweight, Energy-Absorbing Metal Foam

Afsaneh Rabiei, an NC State Professor in the Mechanical and Aerospace Engineering Department, founded Raleigh-based startup Advanced Materials Manufacturing. This picture shows a 100% steel composite metal foam manufactured by powder metallurgy sintering (image courtesy of Afsaneh Rabiei)

Can something made out of 100% steel weigh as little as aluminum?

The answer is yes. And NC State Professor Afanseh Rabiei started Raleigh-based Advanced Materials Manufacturing once she figured it out. Now the startup is one of the semifinalists for NC IDEA’s $50K SEED grants.

After Rabiei earned her PhD in advanced materials from the University of Tokyo, focusing on metal matrix composites, she conducted post-doctoral research at Harvard University focusing on metal foam. When she became a professor of advanced materials at NC State in the Mechanical and Aerospace Engineering Department, she combined the two and spent 20 years figuring out how to make a metal matrix with foam structures that is both lightweight and strong. 

“Other metal forms are very weak, and in general people thought that if you make a metal form stronger you will lose parts of its cushion ability,” Rabiei said. “But actually what we did was to create this material that has good cushion ability and good strength at the same time, and that is the really revolutionary benefit of our technology,” . 

The lightweight composite metal foam that Rabiei created can be used in a myriad of places—anywhere from car bumpers to helmets and body armor to medical devices, buses, helicopters, vehicle armors, tools and even containers carrying hazardous materials and explosives. The porous, energy-absorbing metal foam helps protect against impact, explosions, fire, vibration, radiation and sound.

Two composite metal foam samples: the top is an aluminum matrix with steel spheres made by casting, and the bottom one is steel spheres-in-steel matrix made through powder metallurgy sintering (image courtesy of Afsaneh Rabiei)

The secret behind the sauce: the metal foam only weighs a fraction of its parent metal due to its porous nature, but provides much more protection due to the air bubbles inside. Rabiei said the material has the best of both worlds: the cushion ability of foam and strength of a composite.

Although the original application of the material was for things like automobile bumpers to protect against accidents, Rabiei said that when the Iraq War happened she realized the material could be used in armor to save lives by absorbing the impact of an explosion or shockwave and protecting against flying fragments. 

Rabiei said there are a myriad of industries—defense, aerospace, transportation, medical devices, tools, etc— that could benefit from the lightweight, energy-absorbing composite metal foam material. For instance, hazardous materials like petroleum or nitrogen gas are typically transported in heavy steel cans, but the composite metal foam is made out of about 30-35% steel and around 60% air, giving it the density of aluminum and thereby making those cans much more energy-efficient and fuel-saving.

The composite metal foam (CMF) material can be made out of various other metals and alloys, such as titanium, steel and aluminum. In every case, the foam weighs 30-35% as much as the parent material. So, a foam made out of titanium—which is lighter than steel—would weigh even less than a steel foam, and if needed, the company can even make a floating composite metal foam that has a lower density than water, Rabiei said.

“I had customers calling me everyday asking for this material, so I thought, O.K., maybe it’s time for me to start a company and commercialize this technology,” Rabiei said. “At this point the faster we can expand our production capabilities, the sooner we can provide this revolutionary material to our customers and protect lives.”