Jae-Hwang Lee, a faculty member in the Mechanical and Industrial Engineering Department at the University of Massachusetts Amherst, is the lead and corresponding author of an article published on November 28 In Science magazine. The article describes special high-tech ballistic testing of natural graphene which demonstrates experimentally for the first time how this material can be used to construct a lighter, more protective, kind of bulletproof vest. See BBC article: http://www.bbc.com/news/science-environment-30246089.
“This is the first experimental demonstration that the natural material graphene can actually perform 10 times more efficiently than what steel does in the protection against a supersonic projectile,” says Lee. “Moreover, it turns out that graphene can even surpass a highly engineered Kevlar armor fabric in double score.”
The title of the Science article is “Dynamic Mechanical Behavior of Multilayer Graphene via Supersonic Projectile Penetration,” which describes research indicating that “multilayer graphene efficiently dissipates the kinetic energy of a penetrating micro-projectile.”
The other authors are Phillip E. Loya, Jun Lou, and Edwin L. Thomas from the Rice University Department of Materials Science and NanoEngineering.
Lee explains that, without experimental proof, the static mechanical strength of graphene has been inspiring researchers to dream of ultimate bulletproof vests, which can dramatically reduce the weight of combat gear for soldiers without sacrificing survivability.
For the extreme dynamical test of the nanoscale material, Lee and his colleagues used a miniaturized ballistic technique in which a micro-bullet (3.7 micrometers in diameter) was propelled by gold gas created by laser ablation, not by gunpowder.
The background of the research is that multilayer graphene is an exceptional anisotropic material due to its layered structure composed of two-dimensional carbon lattices. Although the intrinsic mechanical properties of graphene have been investigated at quasi-static conditions, its behavior under extreme dynamic conditions has not yet been studied.
As the authors summarize their research, “We report the high-strain-rate behavior of multilayer graphene over a range of thicknesses from 10 to 100 nanometers by using miniaturized ballistic tests. Tensile stretching of the membrane into a cone shape is followed by initiation of radial cracks that approximately follow crystallographic directions and extend outward well beyond the impact area. The specific penetration energy for multilayer graphene is about 10 times more than literature values for macroscopic steel sheets at 600 meters per second.”
The research team’s microscopic ballistic results reveal that the superior in-plane speed of sound, high strength, stiffness, and structural anisotropy make multilayer graphene an extraordinary armor material exhibiting excellent impact energy delocalization under a supersonic penetration event.
The Science article concludes that “As large-scale production of graphene-based composite materials is becoming possible, other graphene-like materials are being studied; the results suggest opportunities for the use of ordered anisotropic nanocomposites for surprising mechanical applications. The good correspondence between the micro- and macroscopic projectile penetration tests, especially in the measured specific energy absorption, suggests the micro-ballistic method with its high energy resolution may offer an effective means for the exploration of high-strain-rate physics of various materials as well as practical advantages in rapid, high throughput testing.”
Founded in 1880 on $10,000 of seed money from the American inventor Thomas Edison, Science has grown to become the world's leading outlet for scientific news, commentary, and cutting-edge research, with the largest paid circulation of any peer-reviewed general-science journal. Through its print and online incarnations, Science reaches an estimated worldwide readership of more than one million. (December 2014)