Quantifying the effects of accelerated weathering and linear drop impact exposures of an American football helmet outer shell material

Abstract

American football helmets are subjected seasonally to a myriad of environmental conditions from expected use and storage and yet are reused without a relational understanding between service life degradation and changes in impact performance. Comprehensive investigations could link rates and degrees of material degradation to scientifically and clinically meaningful changes in helmet performance. Therefore, the purpose of this research was to preliminarily quantify the effects of accelerated weathering on (1) colorimetric, chemical, fluorescent, and thermal properties; (2) surface and bulk mechanical properties; and (3) impact performance of an American football helmet outer shell material. Helmet-grade plaques were exposed to 480 h of accelerated weathering. Surface-specific shifts (p < 0.05) in colorimetric, chemical, fluorescent, thermal, and mechanical properties were observed at the plaque surface. Plaque-derived tensile specimens underwent monotonic tensile testing, and the photodegraded ∼1% of the Weathered plaque surface thickness led to 10%, 12%, and 9% increases (p < 0.05) in Young’s modulus, yield stress, and ultimate tensile stress, respectively. Impact performance was analyzed with a protocol attempting to employ expected on-field impact conditions. Weathered and Non-weathered helmet surrogate systems managed impact energy progressively less effectively across five repetitive trials (p < 0.05); yet the absence of significant Weathered differences demonstrated that the plaque–foam systems performed similarly. Results identified a battery of diagnostic tools to characterize the degradation of outer shell material exposed to accelerated weathering. Thus, the comprehensive approach herein may be used toward the evaluation of additional service life exposures, as well as examine on-field deterioration of full helmet outer shells.

Development of a non-destructive method to measure football facemask stiffness

“…[15][16][17][18][19][20][21][22][23][24][25][26][27] To save financial and temporal costs in the development phase of novel helmet component designs, it is necessary to evaluate the performance of individual components prior to integrating new components into existing helmet systems. Previous research has evaluated the performance of the external helmet shell, 15,[18][19][20]26 the internal padding, 17,[21][22][23]27,28 and the chin strap, 24,25 but the impact performance of a football facemask has received limited research attention. On field impact exposure research has demonstrated that 30%-40% of a season's worth of football head impacts occur to the front quadrant of the helmet system.…”