Invited: Ballistic Impacts of a Full-Metal Jacketed (FMJ) Bullet on a Validated Finite Element (FE) Model of Head-Cushion-Helmet

In order to determine the severity of the head injuries sustained from ballistic impact orientation and to investigate the effectiveness of the cushioned combat helmet in protecting the head from ballistic impact, series of ballistic impact simulations (frontal, lateral, rear and top) of FMJ bullet on a subject-specific FE head model, which are based on National Institute of Justice (NIJ) test standard. Two different designs of helmet interior cushion, namely the strap-netting system and the Oregon Aero (OA) foam, are adopted in this study. In general, the head experiences highest G in rear impacts among all impact orientations. The FE simulations also show that the use of OA foams helps to reduce frontal impact G forces and thus offers better protection from all various impact orientations except for the top impact in which the presence of air gap in the strap-netting configuration helps to mitigate the stress transmission to the intracranial contents. The OA cellular foams are more effective in limiting the transmission of force by being able to absorb more energy, via plateau characteristic prior to foam densification, compared to the stiffer linear elastic front cushion of strap-netted helmet. In addition, simulated intracranial pressure (ICP) of the helmet-cushion-subject-specific-head assembly has been benchmarked with the experimental ventricular pressure values from impact tests on human skulls filled with silicone gel.