EFFECTS OF RAPID REPEAT COMPRESSIVE LOADING ON FOOTBALL HELMET ELASTOMERIC AND TPU ENERGY ABSORBING MATERIAL PERFORMANCE DURING HIGH HUMIDITY AND TEMPERATURE CONDITIONS

摘要

Helmet energy absorbing (EA) pad materials are needed to reliably attenuate contact-impact forces and reduce head injury risks to safer levels for a player during game or practice sessions that are likely to involve “repeated head impacts” and EA pad degradation from hot moisture effects (i.e. Hot-Wet), such as that generated by heat and moisture of player head sweating where pad temperatures can exceed 46 degrees Celsius. Prior testing has shown that helmet EA padding tended to soften during use in the Hot-Wet condition. EA pad softening during repeat loading may be beneficial if: 1. Sufficient helmet crush space is available to eliminate high head loading caused by EA pad “bottoming-out” against the stiff helmet shell; and, 2. EA pad mechanical properties are able to fully recover after initial impact so that safe EA levels are not deteriorated after first impact. Quasi-static (QS) testing of various EA pad types, coupled with dynamic impact testing of different helmet designs, were used to demonstrate how EA materials respond to combinations of Hot-Wet effects and repeat impact loadings at different impact energy levels. The EA materials tested included: resilient foams; Gel Foams; Styrofoam; TPU thermoplastic configurations. The QS Cyclic load testing showed that full recovery of EA levels tended to be diminished after the first compression. The degraded EA performance was also noted in increases of head impact response measures of head forms fitted to helmets that used various combinations of the EA materials and were tested at different impact energy levels and Hot-Wet conditions. Repeat impact test results showed that, with increasing impact energy, the repeat impact head injury risk Hot-Wet measures generally exceeded ambient and initial Hot-Wet results by increases as high as 40 percent in some helmet designs. The increased head injury risk measures indicate need for more research and understanding of EA pad response during Hot-Wet and repeat impact conditions so as to help develop uniformly safe and lower risk helmet designs.