While graphene is already known for being the world's strongest material, most studies have focused on its tensile strength – that's the maximum stress that it can withstand while being pulled or stretched, before failing. According to studies conducted at Houston's Rice University, however, its ability to absorb sudden impacts hadn't previously been thoroughly explored. As it turns out, the material is 10 times better than steel at dissipating kinetic energy. That could make it an excellent choice for lightweight ballistic body armor.
The research was led by Rice materials scientist Edwin Thomas and assistant professor Jae-Hwang Lee of the University of Massachusetts, Amherst.
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For their small-scale tests, they used sheets made up of multiple layers of graphene. These were stacked together and held in place in a stage mount. Although up to 300 layers were used at a time, the total thickness of the sheets ranged from just 10 to 100 nanometers – keep in mind that each layer was just one carbon atom thick.
They then shot microscopic spheres into those sheets, at speeds of up to 3 km (1.9 miles) per second. The scientists did so using an advanced version of a technique that they had developed previously, in which a laser pulse is fired onto one side of a gold surface, causing so-called glass "microbullets" to fly off the other side at high speed.
A microbullet traveling at supersonic speed is captured in this composite of three timed images, as it makes its way toward a suspended sheet of multilayer graphene (Image: Thomas Research Group/Rice University)
When these bullets hit the graphene, it deformed into a cone shape around them before ultimately breaking and letting them through. In the three nanoseconds before it broke, however, the deforming graphene absorbed a huge amount of the bullets' kinetic energy – the scientists estimate that the transferred energy traveled through the material at a speed of 22.2 km (13.8 miles) per second, which is faster than any other known material.
"The game in protection is getting the stress to distribute over a large area," said Thomas. "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."
He now plans on demonstrating that if scaled up, graphene sheets could be used in applications such as bulletproof body armor, or even in coverings that would help protect spacecraft from high-velocity orbital debris.
A paper on the research was recently published in the journal Science.
Thomas describes the research in the video below.
Source: Rice University