Impact reconstruction from damage to pedal and motorcycle helmets

Abstract

Pedal and motorcycle helmets offer a high level of protection to the wearer’s head. There is a need to review and assess the performance offered by helmets, so that helmet design and test standards can be optimized. One input into this process is crash reconstruction. Helmeted crash cases can be collected and examined, leading to insights into impact severity, helmet performance and injury outcomes. However, it is unclear to what extent residual helmet damage reflects the impact characteristics. This paper addresses this issue using controlled laboratory impact tests. Two pedal cycle and three motorcycle helmet models were tested with an ‘M’ size headform in impact energy attenuation tests from 1 m, 2 m and 2.5 m. Headform acceleration, impact force and post-impact deformation were measured. The dynamic deformations were measured with three methods: video, kinetic energy and an analytical approach using impact force and liner yield stress. All five models offered highly repeatable performance in terms of impact energy attenuation and acceleration management in radial impacts across the impact severities. The results showed that the Standards Australia certified helmets provided impact protection to the head in impacts that greatly exceeded the impact energy attenuation performance requirements of those standards. The residual and dynamic deformation measurements were correlated with drop height and headform acceleration for pedal cycle helmets. The results indicate that the residual deformation observed in a pedal cycle helmet collected from a crash can be used to estimate the impact severity and, after undertaking exemplar impact tests on the same model helmet, the head impact acceleration. However, the residual deformation measured on the three motorcycle helmets was not correlated with the drop height, which indicated that, within the limits of this study, estimating crash severity from motorcycle helmet damage is not reliable.