Who needs science fiction? Nature is a wealth of imaginative plot twists. Take carbon. Carbon is common. It’s the fourth most abundant element in the universe. And yet, carbon is also exceptional.
It’s the elemental keystone of terrestrial life. It stores and releases enough energy to power industrial revolutions. And flakes of the stuff, first peeled off graphite with scotch tape, might one day repel bullets and shield spacecraft.
Experimenting with the one-atom-thick sheets of carbon known as graphene, Researchers at Rice University recently wrote the material’s properties make it exceptionally good at dissipating the energy of incoming projectiles.
Prior research had firmly established graphene’s tensile strength—its ability to stretch without breaking—but no one had measured its ability to absorb an impact. As it turns out, according to Rice materials scientist, Edwin Thomas, because graphene is stiff, strong and elastic it is very, very good at spreading out kinetic energy.
The lab fired microscopic “bullets” at 3 kilometers per second—faster than bullets fired from an AK-47—into graphene sheets of varying thickness and captured the impacts on high-speed camera to see how well they absorbed the energy.
“The game in protection is getting the stress to distribute over a large area,” Thomas said. “It’s a race. If the cone can move out at an appreciable velocity compared with the velocity of the projectile, the stress isn’t localized beneath the projectile.”
Analysis of the impacts showed the graphene behaved like a stretchy membrane, rapidly spreading the impact across the target’s surface. Though the bullets penetrated the graphene, the pattern and size of the hole yielded key clues to how the material absorbed the energy.
The researchers found the rate graphene distributed the impact was faster than any other known material. And although graphene is one of the lightest materials in existence, Thomas said they showed, per unit of weight, it is on average 10 times better than steel at taking a hit.
Future applications might include lightweight bulletproof materials for the military or law enforcement or graphene-skinned spacecraft that are better prepared to deal with micrometeor impacts in space.
The group is working with NASA and the military to show their results can have practical macroscale uses.
Graphene’s ability to resist impacts is the latest in a long string of intriguing characteristics and potential functions. Other properties include supercapacitance, high conductivity, flexibility, transparence, and low-weight strength.
At present, the material in its purest form is still confined to the lab and remains too costly to find significant commercial use. However, researchers are working on a variety of production techniques. Alongside the Human Brain Project, the EU is dedicating a billion euros to graphene research over the next decade. Some believe prices will decline significantly.
If that happens, proposed technologies include lightning-quick graphene computer chips, fast-charging, environmentally friendly batteries, flexible and transparent touch displays, invisibility cloaks, effective water filters for desalination—and yes, perhaps even lightweight shielding to repel the stray bullet on Earth or micro-meteor on a trip to Mars.
