A few months ago, we discussed how nanocellulose boasts of a much higher stiffness than both Kevlar and steel. The researchers at the Rice University found out that graphene is not too far behind in that respect – with its ability to perform twice as well as Kevlar when it came to dissipating the energy of a bullet. In addition, it was a whopping eleven-times as effective as steel, during the demonstration of the said test.
This testing was done by setting up a miniature firing range inside the lab, with the novel study focusing on the strength of graphene sheets and their potential capacity as armor materials. In fact, graphene was chosen because of its intrinsic toughness that comes by virtue of its one atom thick structure composed of resolute honeycomb lattice (in an atomic scale). However, the predicament related to how graphene is not readily available in its mass-scale, with the supermaterial incredibly making its lab debut just eleven years ago, in 2003.
So, the scientists had to settle for a small scale experiment that could still assess the adequacy of graphene as a high-grade armor. To that end, their mini firing range consisted of a laser setup that could vaporize gold filaments. The resultant explosion accelerated micron-sized glass bullets towards a set graphene target composed from an arrangement of over 10 (to even 100) graphene sheets. These tiny bullets traveled with a speed of 10,800 km per hr (6,700 mph), which is around one-third the velocity of a conventional bullet. Finally, electron microscopy was used to gauge the effectiveness of graphene sheets in absorbing the flurry of bullet impacts.
The results showed a very interesting side to graphene, with the material depleting the kinetic energy of the bullets by stretching backwards – much like a trampoline effect. According to the researchers, this unique energy-dissipating action occurred due to graphene’s high stiffness that is combined with its low density. In essence, its structure allows for the dispersion of the impact throughout the sheet, which ultimately aids in expending the brutal force of a bullet.
When translated to figures, graphene performed 2-times better than Kevlar, while showing 11-times better result than steel. For example, the graphene sheet exhibited its capacity to absorb 0.92MJ/kg of projectile energy. In comparison, steel conventionally accounts for absorption of 0.08MJ/kg of projectile energy. Of course, there is practical realm that exists beyond just numbers and figures. In that regard, scientists first have to find a way to commercially produce graphene (for bullet proof vests), and that too with a low cost factor.
The study paper was published in the Science journal.
Image Credits: Jae-Hwang Lee