Conference Paper

The effect of hair and football helmet fit on headform kinematics

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Abstract

This study examined the effect of hair and helmet fit on headform kinematics during side and eccentric impact locations at ~7.4 m/s. Compared to the no hair and tight fit condition, the presence of hair and a loose helmet condition resulted in ~10% lower PLA, PAA, and Δω at the SD location and similarly lower PLA and PAA at the EC location. These findings indicate that hair at the head-helmet interface and/or a loose helmet attenuate a head impact, possibly by allowing more movement of the helmet relative to the headform during the impact. Interestingly, the pattern of pairwise differences in these variables suggests that the two effects are not superimposed, a finding that further suggests there is a limit to the benefit of looser coupling between the head and helmet. Neither hair nor helmet fit was a significant factor for Δω at the EC location. This unexpected outcome may be due the lower PAA values for the hair/loose conditions being offset by the slightly (though not significantly) longer Δt, resulting in an aggregate effect, i.e., Δω that was not different. Further work is needed to assess this and other potential explanations.

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... The literature indicates that alterations that reduce friction between the head and liner can have a modest effect on PAA. 24 Specifically, Bonin et al. 24 observed that the addition of a human hair wig to an ATD donning an American football helmet reduced PAA by approximately 300 rad/s 2 (5-6%) during blunt impacts to the side of the head performed on a pneumatic ram. However, in Bonin et al. 24 µ s was not directly measured. ...
... The literature indicates that alterations that reduce friction between the head and liner can have a modest effect on PAA. 24 Specifically, Bonin et al. 24 observed that the addition of a human hair wig to an ATD donning an American football helmet reduced PAA by approximately 300 rad/s 2 (5-6%) during blunt impacts to the side of the head performed on a pneumatic ram. However, in Bonin et al. 24 µ s was not directly measured. ...
... 24 Specifically, Bonin et al. 24 observed that the addition of a human hair wig to an ATD donning an American football helmet reduced PAA by approximately 300 rad/s 2 (5-6%) during blunt impacts to the side of the head performed on a pneumatic ram. However, in Bonin et al. 24 µ s was not directly measured. It has also been shown that MIPS ® systems, which reduce the friction between the liner and helmet shell can result in a reduction in PAA during blunt impact tests. ...
Article
Introduction The purpose of this study was to compare the rotational blunt impact performance of an anthropomorphic test device (ATD: male 50% Hybrid III head and neck) headform donning an Advanced Combat Helmet (ACH) between conditions in which the coefficient of static friction (μs) at the head-to-helmet pad interface varied. Materials and Methods Two ACHs (size large) were used in this study and friction was varied using polytetrafluoroethylene (PTFE), human hair, skullcap, and the native vinyl skin of the ATD. A condition in which hook and loop material adhered the headform to the liner system was also tested, resulting in a total of five conditions: PTFE, Human Hair, Skullcap, Vinyl, and Hook. Blunt impact tests with each helmet in each of the five conditions were conducted on a pneumatic linear impactor at 4.3 m/s. The ATD donning the ACH was impacted in seven locations (Crown, Front, Rear, Left Side, Right Side, Left Nape, and Right Nape). The peak resultant angular acceleration (PAA), velocity (PAV), and the Diffuse Axonal Multi-Axis, General Evaluation (DAMAGE) metric were compared between conditions. Results No pairwise differences were observed between conditions for PAA. A positive correlation was observed between mean μs and PAA at the Front (τ = 0.28; P = .044) and Rear (τ = 0.31; P = .024) impact locations. The Hook condition had a mean PAV value that was often less than the other conditions (P ≤ .024). A positive correlation was observed between mean μs and PAV at the Front (τ = 0.32; P = .019) and Right Side (τ = 0.57; P < .001) locations. The Hook condition tended to have the lowest DAMAGE value compared to the other conditions (P ≤ .032). A positive correlation was observed between the mean μs and DAMAGE at the Rear (τ = 0.60; P < .001) location. A negative correlation was observed at the Left Side (τ = -0.28; P = .040), Right Side (τ = -0.58; P < .001) and Left Nape (τ = -0.56; P < .001) locations. Conclusions The results of this study indicate that at some impact locations kinematic responses can vary as a function of the friction at the head-to-helmet pad interface. However, a reduction in the coupling of the head-helmet pad interface did not consistently reduce head angular kinematics or measures of brain strain across impact locations. Thus, for the ACH during collision-type impacts, impact location as opposed to μs seems to have a greater influence on head kinematics and rotational-based measures of brain strain.
... 12,23 Our work extends these findings by showing that differences in headform conditions also need to be considered when making inter-laboratory comparisons of oblique helmet impacts. One or more layers of stockings are often used to cover the vinyl nitrile skin of the Hybrid III headform to reduce the friction between the helmet and the headform, [6][7][8]22,34 whereas hair has been considered less frequently during helmet testing. 7,29 Although we included a human-hair condition, the amount and length of this hair does not represent all human hair conditions and the shear properties that exist between a human scalp and the skull were missing. ...
Article
Bicycle helmets are designed to attenuate both the linear and rotational response of the head during an oblique impact. Here we sought to quantify how the effectiveness of one popular rotation-attenuating system (MIPS) varied across 3 test headform conditions (bare, covered in stockings, and hair), 3 oblique impact orientations, and 4 impact speeds. We conducted 72 freefall drop tests of a single helmet model with and without MIPS onto a 45° angled anvil and measured the peak linear (PLA) and angular acceleration (PAA) and computed the angular velocity change (PAV) and brain injury criterion (BrIC). Across all headform conditions, MIPS reduced PAA and PAV by 38.2 and 33.2% respectively during X-axis rotation, 47.4 and 38.1% respectively during Y-axis rotation, and 22.9 and 20.5% during a combined ZY-axis rotation. Across all impact orientations, PAA was reduced by 39% and PAV by 32.4% with the bare headform while adding stockings reduced PAA and PAV by 41.6 and 36% respectively and the hair condition reduced PAA and PAV by 30.2 and 24.4% respectively. In addition, our data reveal the importance of using consistent headform conditions when evaluating the effect of helmet systems designed to attenuate head rotations during oblique impacts.
Article
Motorcyclists are at high risk of head injuries, including skull fractures, focal brain injuries, intracranial bleeding and diffuse brain injuries. New helmet technologies have been developed to mitigate head injuries in motorcycle collisions, but there is limited information on their performance under commonly occurring oblique impacts. We used an oblique impact method to assess the performance of seven modern motorcycle helmets at five impact locations. Four helmets were fitted with rotational management technologies: a low friction layer (MIPS), three-layer liner system (Flex) and dampers-connected liner system (ODS). Helmets were dropped onto a 45° anvil at 8 m/s at five locations. We determined peak translational and rotational accelerations (PTA and PRA), peak rotational velocity (PRV) and brain injury criteria (BrIC). In addition, we used a human head finite element model to predict strain distribution across the brain and in corpus callosum and sulci. We found that the impact location affected the injury metrics and brain strain, but this effect was not consistent. The rear impact produced lowest PTAs but highest PRAs. This impact produced highest strain in corpus callosum. The front impact produced the highest PRV and BrIC. The side impact produced the lowest PRV, BrIC and strain across the brain, sulci and corpus callosum. Among helmet technologies, MIPS reduced all injury metrics and brain strain compared with conventional helmets. Flex however was effective in reducing PRA only and ODS was not effective in reducing any injury metrics in comparison with conventional helmets. This study shows the importance of using different impact locations and injury metrics when assessing head protection effects of helmets. It also provides new data on the performance of modern motorcycle helmets. These results can help with improving helmet design and standard and rating test methods.
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