The Advanced Materials Research Lab (AMRL) at North Carolina State University, USA, is reported to be developing a new class of metallic foam that combines the benefits of metal matrix composites with metallic foams. The composite metal foam (CMF) could have numerous applications and has recently been shown to stop armour-piercing bullets, as well as being able to shield radiation and offer extremely good thermal insulation.
The research has focused on developing the technology to process composite metal foams through both Powder Metallurgy and casting techniques. The CMF has up to eight times higher energy absorption compared to any other metal foam made from similar materials and its energy absorption is almost two orders of magnitude higher under loading compared to the original bulk materials.
Afsaneh Rabiei, Professor of Mechanical and Aerospace Engineering at NC State, has worked on developing CMFs and investigating their unusual properties. With support from the US Department of Energy’s Office of Nuclear Energy, Rabiei and her team showed that CMFs are very effective at shielding X-rays, gamma rays and neutron radiation. Rabiei has also published work demonstrating that these metal foams handle fire and heat twice as well as the plain metals they are made of.
Other potential applications of CMFs is in blast and ballistic armour. The results of Rabiei’s experiments have shown that CMFs were able to absorb the major portion of the total kinetic energy of projectiles effectively, in addition to stopping both types of type III and type IV (armour piercing) projectiles. Further studies on the capability of CMFs to protect against larger threats and blast are still ongoing.
“We could stop the bullet at a total thickness of less than an inch, while the indentation on the back was less than 8 millimetres,” stated Rabiei. “To put that in context, the NIJ [National Institute of Justice] standard allows up to 44 mm indentation in the back of an armour.”
The researchers have also subjected the material to high speed impact testing for automotive and train applications. These tests showed very high energy-absorption capabilities at a variety of impact speeds from quasi-static up to 100 meters per second. This indicates the potential for utilising CMFs in crash energy management systems in trains, cars, buses.