Laser-Induced Projectile Impact Test Confirms Graphene's Strength

Graphene's great strength appears to be determined by how well it stretches before it breaks, according to Rice University scientists who tested its properties by firing microscopic projectiles at multilayer sheets of the material. The technique could help measure the strength of a wide range of materials. The Rice University lab of materials scientist Edwin Thomas proved that graphene is on average ten times better than steel at dissipating kinetic energy. The lab pioneered its laser-induced projectile impact test (LIPIT), which uses the energy from a laser to drive microbullets away from the opposite side of an absorbing gold surface at great speed. In 2012, they first used an earlier version of LIPIT to determine the properties of multiblock copolymers that could not only stop microbullets but also completely encase them. Since that study, Thomas and his team have enhanced their technique to fire single microscopic spheres with great precision at speeds approaching 3 kilometers per second, much faster than a speeding bullet from an AK-47. The experiments revealed graphene to be a stretchy membrane that, in about 3 nanoseconds before puncture, distributes the stress of the bullet over a wide area defined by a shallow cone centered at the point of impact.

Transcript

00:00:00 [Music] what we uh explored was the ability of thin graphine sheets and represented by this uh black film uh to stop a projectile represented by this pingpong ball and the uh size of the actual projectile it's a micro bullet it's only about three microns uh in diameter a human hair is around 50 microns so this is considerably thinner than you know

00:00:32 like a tenth of the size of a human hair and the thinness of the membrane is also down on the scale well below a human hair and the size of this sphere relative to the thickness of this membrane is about what we do in our experiments and we shoot this sphere at a very high rate around a kilometer per second so uh bullets typically are below a kilometer per second in speed and the

00:00:54 sphere at these high rates carrying kinetic energy impacts this thin membrane presses against it pushes it forward and a cone of deformation develops with the sphere at the center and because graphine is very very strong and it's very very stiff and it's very very low density this cone spreads out to quite a distance in the material and the kinetic energy of the sphere is

00:01:19 transferred to the membrane before it pushes through and then eventually exits on the other side and in our experiments we can measure the velocity and therefore the kinetic energy of the sphere in front of the membr mebrane before it hits and after it's passed through the membrane and therefore calculate the difference in those two energies as the energy that was required

00:01:38 to pass through the membrane and when we compare the behavior of graphine thin films to that of other materials for example uh Steel on an equal weight basis graphine is 10 times better than steel at absorbing energy out of micro bullets so one of the um uh characteristics of a material that is dissipating a lot of energy is the amount of material that's involved in

00:02:02 the in the penetration event what we've shown here in these these images is a material which doesn't absorb very much energy uh in this case uh it just has a circular hole the same size as a sphere where the sphere penetrated through without losing much energy and uh also we have pictures of the graphine films which are much stronger and absorb much more energy and you can see the

00:02:23 extensive damage which is in an area several diameters of the sphere uh bigger than the size of the sphere you could kind of demonstrate this at home when you uh wanted to look at if you're trying to punch through a piece of paper it will make a small hole whereas if you push uh against something like a stretchy piece of Saran uh wrap will deform a large cone and then eventually

00:02:46 punch through but the deformation of the film will be much more extensive and the energy it took to push through this Rand if it was on the same thickness as the paper would be a lot more we've understood some of the principles of what makes graphine such a excellent protection material and because graphine is so lightweight it could be employed for ballistic protection for the war

00:03:05 fighter and even in satellites and the space station for protection against microm meteorites