Composite metal foam, a material developed by the Advanced Materials Research Lab, is a high strength, lightweight material capable of pulverizing armor piercing bullets upon impact. CMF’s have also been found to be heat resistant and can block X-rays, gamma rays and neutron radiation.
Afsaneh Rabiei, a professor in the Department of Mechanical and Aerospace Engineering and director of the Advanced Materials Research Laboratory, developed CMFs and has been studying their potential uses and special properties.
“The composite metal foam is a material made of the combination of the idea of metal matrix composites and metal foam, so normally a foam is made up of a bunch of porosities — no matrix in between,” Rabiei said.
Regular metal foams are very porous with different sized porosities and a low strength, according to Rabiei. Composite metal foams contain uniformly sized hollow spheres that help increase the strength of the material.
“If you look at two rulers for example, a tall ruler and a short ruler, you compare that and [bend] them and the tall ruler buckles faster,” Rabiei said. “Similar to that, larger porosities buckle faster. By providing a uniform size porosity, we take out that possibility of premature failure and we kind of spread the load all over the material.”
To make the CMFs, molten aluminum is cast over the hollow spheres, metal powder is mixed in and then it is baked in a furnace. The main focus of the process is to make sure the spheres are not melted or crushed and to get the right packing of hollow spheres, according to Rabiei.
A solid portion of metal is heavier compared to the CMF’s weight, which can also bear heavier loads than its solid counterpart. As seen in the example video on Rabiei’s website, CMFs do not crack when completely squeezed down to a small size.
“It took us like a year and a half to make our first sample that squeezed down to that level and that was really a very happy moment of my life,” Rabiei said.
With this major milestone, Rabiei realized that the CMFs were going to make their mark in the future.
“There are a lot of applications like car bumpers and high speed trains, and the next thing you may think is obviously for armors,” Rabiei said.
The reason that the material is heat resistant is very similar to the way Styrofoam cups work when they are filled with hot coffee. The air bubbles in Styrofoam provide shielding from heat, and the same concept applies to CMFs with the air inside its porosities, according to Rabiei.
“We put it against 800 degrees [Celsius] for 30 minutes, and it really didn’t do anything,” Rabiei said. “The piece of metal was the same shape and size, and everything is the same. It took four minutes for a piece of steel to transfer the heat from the bottom to the other side. It’s a very thin layer, it was not very thick and it took eight minutes for the composite foam to heat up to the other side.”
The CMF’s heat resistance opens up more possibilities in how it can be used, such as with nuclear casks, which are used to transport and store nuclear waste. The CMF would prevent puncturing in the cask if it is dropped, and its lightness could reduce the effort to transport them, according to Rabiei.
CMFs could also be used in space because of these various properties. Using the material in lunar stations, the reentry of spacecraft or satellites is also a goal, according to Rabiei.
“My goal is to see this actually helping people, so I always have said that if someone walked out of an accident or a major issue safe because of my material I think I have accomplished my lifetime goal,” Rabiei said.
Funding is also an important consideration in the research and work being done with the CMFs. The Department of Energy’s Office of Nuclear Energy and the National Science Foundation have given support, according to Rabiei. Typically Rabiei’s lab is used to create the CMFs, but when bigger portions had to be made, labs at NASA and other places were used.
“When I see it perform the way I’m expecting, it just really makes my day,” Rabiei said. “It really gives me a lot of energy to just jump through any hoops and keep up with the work that is in front of us.”
