Consequences of nonpenetrating projectile impact on a protected head: study of rear effects of protections.

BACKGROUND: Police and armed forces have helmets that can now stop handgun bullets and even a certain category of rifle bullets. The trend is to increase the ballistic limits of helmets, but injuries caused by nonpenetrating impacts are not well understood. The helmet defeats the projectile and creates a local cone of deformation that impacts the head a second time. The term "rear effects" describes the behind-armor blunt trauma caused by the nonpenetrating impact.
METHODS: To analyze rear effects on the skull, an experimental study was associated with parametric simulations on a three-dimensional finite element model. Transfer of energy throughout the head was tested on 30 human skulls filled with a silicone gel. The magnitude of contact forces on the skull surface and the pressure levels in the skull were recorded during a reference impact.
RESULTS: A biomedical approach by pathologic findings and radiographs showed very localized fractures. The protection brought by the diploe in the multilayered bone was confirmed and characterized by numerical simulations.
CONCLUSION: This first step toward a better understanding of the rear effect phenomenon in relation to its consequences on brain tissue will lead to the design of more efficient protections.