Design of an optimally safe football helmet system requires an awareness and evaluation of the factors and variables that can adversely affect the impact attenuating performance of energy absorbing (EA) pad materials needed to minimize transmission of linear and rotational forces applied to the head so that risk of head injury is reduced. For instance, player head sweating can induce high temperatures and moisture within a helmet system (i.e. a Hot-Wet condition) which can result in degradation of helmet EA capacity and cause increased measures of head injury risk levels, which are often used for comparative evaluation of helmet designs. In this study, a “multivariable” experimental method was utilized to demonstrate an efficient means for assessment and comparison of currently representative adult and youth football helmet system designs when subjected to a range of variables that included, among other factors: temperature-moisture effects; impact energy; and, repeat impacts. Both quasi-static (QS) compression testing of commonly used EA materials and dynamic impact testing of full helmet systems were conducted and the results are presented in Tables and graphic form. The EA pad types that were QS tested included: Thermoplastic-Polyurethane (TPU) “waffle shaped” EA pad configurations; load rate sensitive “Gel” foam padding; and, dual and single density elastomeric foam padding. Dynamic helmet repeat impact tests were conducted by using a pendulum impact test device where various helmet designs were mounted to a Hybrid-III head and neck system and impacted against a non-yielding surface at energy levels of 108J and 130J after being subjected to ambient and Hot-Wet conditions. The QS tests showed that a short Hot-Wet soak time of only a few hours’ noticeably diminished EA levels. Also, the dynamic full helmet system testing demonstrated that the “Hot-Wet” condition tended to degrade helmet impact attenuation performance such that, depending on the size and type of EA material provided in the crush zone, head injury risk measures tended to increase. Finally, examples of the use and benefits of a “multivariable” experimental method for helmet injury risk assessment, not reported on previously, are provided.
The helmet is the primary means for providing head impact protection to adult and youth football players through use of energy absorbing (EA) materials placed in a crush zone located between the head and helmet shell. Ultimate safety performance of the helmet requires uniformly consistent, repeatable and reliable attenuation of the impact energy so as to minimize head injury potential throughout the helmet. However, quasi-static materials tests and dynamic helmet testing results, reported on herein, show that EA materials of current and older helmet designs are susceptible to large levels of EA degradation, or softening, when subjected to a “hot-wet” condition caused by high temperatures and high humidity, such as that produced from the sweat of a player. Depending on the size of the crush zone, and other factors, this condition can lead to increased head impact loads. The standard football helmet certification criteria do not address the issue of “hot-wet” EA degradation. Dynamic helmet testing analyzed in this study consisted of two methods. One method used the standard helmet certification approach where a human responding head form and helmet are dropped vertically, along a twin guide wire set-up, onto a soft rubber pad. The second method employed use of a human responding Hybrid-III head and neck that was incorporated into a free pendulum impact set-up where impact took place on a non-yielding surface and both direct contact impact injury potential and rotational injury aspects of the helmet performance were measured. The dynamic tests were conducted with various size head forms, energy levels, and impact speeds that ranged from the 5.5 m/s level, used in helmet certification, on up to higher speeds of 7.0 m/s that is more consistent with a “5-second 40-yard dash” speed. Based on equal kinetic energy impact comparisons, the two dynamic approaches showed that helmets that were impacted onto the soft elastomeric pad surface produced artificially lower indications of head injury severity than did the helmets tested against the non-yielding surface. The results also showed large variations and inconsistencies of impact attenuation within a specific helmet design, depending on impact location or region being tested. Also, dynamic impact testing was applied with both ambient and 3-hour “hot-wet” soak conditions applied to the EA padding of adult and youth helmets. These results showed that the relatively newer EA pad designs and the older type elastomeric foam EA pads were sensitive to “hot-wet” degradation for soak times as low as 3-hours, which is consistent with game or practice time situations. Finally, as noted above, it was shown that, depending on the size of the crush zone, this EA degradation factor could lead to increased head loads and injury severity measures. The results suggest the need for additional research on the above to enhance helmet safety.
This study demonstrates the use of efficient inferred statistical “factorial methods” for scientifically evaluating, with a relatively few tests, the rear-impact occupant “head and neck injury risk” performance of 2 different types of vehicle front seats, with adjustable headrests, when various size occupants are subjected to high and low impact severities. The 2 seat types studied included the stronger “belt-integrated seat” (BIS) designs, with restraints attached and having strength levels beyond 14 kN, and the more common but weaker single recliner (SR) seats, without attached restraints and having only about 3.2 kN strength. Sled-body-buck systems and full vehicle to barrier tests were run with “matched pairs” of surrogates in the 2 seat types at speed changes of 12.5 to 50 kph. Three sizes of Hybrid-III adult surrogates (i.e. 52 kg small female, 80 kg average male, and an average male surrogate ballasted to about 110 kg) were used in the evaluations. Also, some tests were run with 6 year-old Hybrid-III child surrogates located behind the front seats due to interest in potential child injury from collapsing front seats. The 2-level factorial method, combined with a biomechanical ratio comparison and a “student-t” test evaluation, were used to compare safety performance of the 2 seat designs. The resulting data analysis indicates that, in the mid to high range of rear impact severity (i.e. 20 to 50 kph), the stronger BIS seat systems tend to provide greatly improved “head-neck” protection over the weaker SR type seats for both the front seated adult occupants and rear seated children. At the low range of impact severity (i.e. 12.5 to 19 kph) there was no significant statistical difference between either seat types, except that the headrests of both could be improved.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.