Light-weight nanostructured composite materials just a few centimetres thick can stop bullets travelling at over 300 m/s - much better than bulk materials such as Kevlar or steel. Yet, little is known about the details of how these materials respond at the nanoscopic scale to high-speed impact. A study in Nature Communications reveals new information about how the structure of bullet-proof materials influences their performance.
The difficulties in studying how composite materials behave under ballistic impact arise from the fact that conventional bullets are millions of times bigger than the nanoscopic structures that determine their properties. To address this, Edwin Thomas and colleagues use high-powered lasers to propel 3.7 micrometre wide beads of silica into composites composed of alternating nanometre-thick layers of rubbery and glassy polymers. This enabled them to obtain detailed images of how the layers deformed under impact by beads travelling at speeds of up to 4 km/s. The results indicate that ensuring that a composite's layers are oriented perpendicular to the path of an incident projectile can improve its performance by up to 30%.