A new metal foam able to stop a speeding bullet is the latest in a new generation of materials with a myriad of different potential uses.
When impacted by a bullet, even a fast-moving projectile shatters into a cloud of dust. The new substance is also significantly lighter than armor plating, making it a perfect material for armor-plating vehicles and people. Consumers could also benefit from this new metal foam, as well as other materials being developed by researchers worldwide.
Composite metal foams (CMFs) have bizarre properties, which allow them to stop even powerful impacts. Researchers tested the latest using 7.62 x 63 millimeter M2 armor piercing projectiles, fired in accordance with standards established by the National Institute of Justice (NIJ). Those performance benchmarks measure the effectiveness of bulletproof vests and armor.
"We could stop the bullet at a total thickness of less than an inch, while the indentation on the back was less than 8 millimeters. To put that in context, the NIJ standard allows up to 44 millimeters indentation in the back of an armor," says Afsaneh Rabiei of North Carolina State University.
Another variety of metal foam developed at Cornell University was able to transform from one shape to another. This substance is composed of a soft alloy called Field's metal, together with a porous silicone foam. Because it is free of lead, it the material may be used within biological systems.
The new CMF developed at North Carolina State University is able to withstand twice the heat of the metals of which it is composed, as well as being twice as fire-resistant. Moreover, the material also blocks some of the most damaging and energetic forms of radiation, including neutrons, X-rays, and gamma rays.
In addition to acting as a bulletproof covering, the material might also be utilized to store nuclear waste, and in the construction of a new generation of airplanes and spacecraft. The foam developed at Cornell could morph into the shape of a wing, transforming an underwater craft into a flying vehicle.
The fact that metal foams are so light, while still delivering a great deal of strength, makes them ideal for a wide range of applications. For a trip like bringing humans to Mars, saving just a small percentage of the weight of a spacecraft could result in a vast savings in fuel and financial outlay.
Metal foams can be manufactured in a number of ways, including casting metal alloys over metallic spheres, creating a structure similar to the one seen on Swiss cheese.
The materials, which were first developed decades ago, can also be constructed by pumping gas through molten metal as it cools. The metal foam developed at Cornell is created by placing foam into molten metal. Placing the foam in a vacuum allows the metal to fill the pores contained within the structure.
Future research will examine how CMFs may be employed in a wide range of practical uses, for uses by industry and consumers.
The analysis of the shape-shifting metal foam was published in the journal Advanced Materials.
