The Influence of Headform/Helmet Friction on Head Impact Biomechanics in Oblique Impacts at Different Tangential Velocities

Óscar Juste-Lorente,Francisco J López-Valdés,Mario Maza,Mathieu Piccand

doi:10.3390/app112311318

Óscar Juste-Lorente, Francisco J López-Valdés + Show 2 more

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https://doi.org/10.3390/app112311318

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Abstract

Oblique impacts of the helmet against the ground are the most frequent scenarios in real-world motorcycle crashes. The combination of two factors that largely affect the results of oblique impact tests are discussed in this work. This study aims to quantify the effect of the friction at the interface between the headform and the interior of a motorcycle helmet at different magnitudes of tangential velocity. The helmeted headform, with low friction and high friction surface of the headform, was dropped against three oblique anvils at different impact velocities resulting in three different magnitudes of the tangential velocity (3.27 m/s, 5.66 m/s, 8.08 m/s) with the same normal component of the impact velocity (5.66 m/s). Three impact directions (front, left-side and right-side) and three repetitions per impact condition were tested resulting in 54 impacts. Tangential velocity variation showed little effect on the linear acceleration results. On the contrary, the rotational results showed that the effect of the headform’s surface depends on the magnitude of the tangential velocity and on the impact direction. These results indicate that a combination of low friction with low tangential velocities may result into underprediction of the rotational headform variables that would not be representative of real-world conditions.

Highlights

According to the World Health Organization, three hundred and seventy eight thousand people died in 2016 as a direct result of a motorcycle collision, amounting to 28% of the world’s road traffic related deaths [1]
The −40% VT case resulted in higher peak resultant linear acceleration and slightly shorter impact durations than the other two tangential velocities. This result might be influenced by the different location of the impact point between the helmet and the anvil, which was dependant on the tangential velocity component, as shown in Figure A3: reducing the magnitude of VT shifted the impact point in the negative
Despite tissue-based metrics such as Maximum Principal Strain (MPS) are desirable for assessing brain injury risk since they are a measure of the primary injury mechanism, this study looked only into four kinematic-based metrics (PLA, Head Injury Criterion (HIC), Brain Injury Criterion (BrIC) and peak of the resultant angular acceleration (PAA))

Summary

Introduction

According to the World Health Organization, three hundred and seventy eight thousand people died in 2016 as a direct result of a motorcycle collision, amounting to 28% of the world’s road traffic related deaths [1]. Despite the proven effectiveness of helmets in the protection of the head [2,3], head injuries are the leading cause of death and long-term disability after a motorcycle crash [4]. The magnitude of the reaction force normal component is related mainly to the height of the rider’s fall on the ground while the reaction force tangential component is associated to the motorcyclist’s travelling speed [10]. The magnitude of this tangential component is directly related to the rotation experienced by the rider’s head

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