Abstract
A comprehensive experimental impact characterization study of novel impact energy absorbing (IEA) materials for sport helmet pads is conducted. These novel pad materials are fabricated using University of Massachusetts Dartmouth’s Flocked Energy Absorbing Material (FEAM). FEAM IEA panels are prepared by flocking 1 to 3 mm long, 6 to 60 denier textile fibers (e. g. nylon or polyester) onto a planar fabric sheet. Here, the deposited flocked fibers are oriented upright to the direction of compressional impact such that energy absorption occurs by the bending, buckling and inter-fiber friction of the upright flock fibers during deformation by impact loading. In this present study, FEAM pad configurations were tested directly via a double lap shear jig and guided weight drop tower. IEA results of a parametric study are thus reported where the fiber material properties such as flock fiber length, diameter (denier), and flock density (number of flock fibers per area) are presented, discussed, and compared with common vinyl nitrile foam. Padding material based on FEAM configurations showed remarkable improvement when compared directly to vinyl nitrile (VN) foam under pre-compression and dynamic shear loading, with a 135% increase in shear strain energy density for the high impact velocity loading condition. Additionally, for low velocity impact conditions, the FEAM based padding materials outperformed with a 49% increase in shear strain energy density as compared to VN foam. The IEA performance of the padding materials, in terms of both linear and angular accelerations, of the sport helmets under impact loads were then evaluated using a custom designed and built linear impactor and instrumented National Operating Committee on Standards for Athletic Equipment head. The effectiveness of padding materials for impact loads from various directions that simulates two helmeted sport athletes in real-time helmet-to-helmet strike/impact are considered. A high-speed camera is used to record and track neck flexion angles and compare them with pad effectiveness to better understand head kinematics of struck players. Under simulated real time impacts, the VN foam padding material generally performed better at higher impact velocities. The best FEAM padding configuration, however, showed a decrease in resultant angular acceleration of the struck player head of 12.9% , 18% , 9.9%, 14.4%, 17.2%, and 14.4% when struck at 6 m/s at the front, front boss, rear, rear boss cg, rear boss nc, and side locations respectively as compared with VN foam padding. Maximum neck flexion angle results determined from the high-speed video footage shows that FEAM materials tend to reduce the maximum neck angle. Maximum neck velocity was also reduced in most impact positions; however, max angular acceleration was only reduced in rear and side impact positions. The best helmet pad designs will therefore need some combination of VN foam and FEAM materials to reduce concussive and mTBI risk across the span of impact velocities and impact locations.