Evaluating the Performance of Helmet Linings Incorporating Fluid Channels

Performance advantages of incorporating fluid channels into a foam made of DERTEX VN600 (vinyl nitrile) are evaluated. This foam has the potential to replace the traditional foam material of helmet liners, like expanded polystyrene (EPS). The experiments involved dropping a certified size E headform vertically onto a flat, solid anvil. Elastically deformable and resilient VN foam outperformed EPS during all impacts. Incorporating a viscous aqueous solution of 30 % by weight glycerin into 3/8 in. (0.95 cm) diameter channels machined through VN foam, reduced the peak headform acceleration by 12 % on first impact compared to VN foam samples without fluid channels. The reduction was 17 % when compared to EPS foam samples. The duration of the first impact increased by 27 % over EPS, significantly lowering the associated head injury criterion values. Repeated impact testing demonstrated an increasing performance advantage of incorporating fluid channels. Samples incorporating 30 % glycerin solution reduced the peak headform acceleration after six impacts by 50 % as compared to EPS.