Designing flocked energy-absorbing material layers into sport and military helmet pads

A systematic study is reported on applying flocked energy-absorbing materials (FEAM) to designing sport and military helmet pad structures. An executed parametric study shows that the impact force absorbing (IFA) properties of FEAM elements are optimized when using (a) higher denier flock fiber (60 to 100 denier) and (b) longer flock fibers (3 to 4 mm length) at higher flock densities. Continuing work focuses on the importance of IFA/areal density ratios in helmet pad functional design. It is found that foam materials like vinyl-nitrile and ethylene vinyl acetate (EVA) inherently exhibit higher IFA/areal density (IFA/AD) ratios than FEAM material structures. With this finding, a new strategy for developing sport and military helmet pads was devised involving the combination of foam and FEAM layer elements. Here, the meritorious properties of foam materials (light weight and excellent IFA properties) and the excellent IFA and breathability (wearer comfort, sweat and heat management) properties of FEAM could be favorably encompassed. A plan was conceived and implemented whereby combination foam/FEAM test pads having high amounts of the high IFA/AD ratio VN-600 or EVA foam layer component were impact tested. By gradually introducing the more comfortable, breathable, body-heat managing FEAM layers into the helmet pad structure, some “trade-off” helmet pad configurations were designed and evaluated. Experiments showed that helmet pad designs having not more than 40% to 50% FEAM content should produce adequate IFA/AD ratio “trade-off” property helmet pad configurations.