June 23, 2010
A presentation given by Dr. Tack Lam, Senior Managing Scientist in the Los Angeles Office, was selected to receive the Society of Automotive Engineers (SAE) Outstanding Oral Award from the SAE 2010 World Congress. Approximately 5% of all presenters are granted this award. The presentation was entitled "Repeated Impacts on a Motorcycle Helmet: What Happens After a Significant Impact?". The paper, authored by Dr. Lam and Dr. Deanna Gates, both from our Biomechanics Practice, addressed issues related to whether significant impact could degrade the protective ability of a motorcycle helmet. The abstract and link to the paper is listed below (registration required).
SAE publication 2010-01-1016: Repeated Impacts on a Motorcycle Helmet: What Happens After a Significant Impact?
It is widely accepted that a motorcycle helmet will reduce the risk of a serious brain injury during an accident through energy dissipation. Currently, there is no literature on what happens to a motorcycle helmet after repeated significant impacts or why it cannot be re-used according to the DOT label. It is also unclear experimentally if the foam liner is permanently affected after repeated impacts. In this study, we repetitively dropped one style of DOT-approved motorcycle helmet using a drop tower system in accordance with FMVSS 218. Helmeted Hybrid III and magnesium headforms were dropped onto a flat anvil with contact to the apical region of the helmets. Strips of pressure-indicating film were placed in the mid-sagittal plane between the foam liner and the headform. Headform accelerations and head injury criterion (HIC) for the Hybrid-III headform were calculated for each drop test. There was a trend for maximum headform acceleration to increase with the number of impacts. The results suggest that a significant impact can degrade the protective ability of the helmet. This was consistently shown in both types of headforms. During the impacts, stress concentrations exceeding the plastic yield of EPS foam were consistently seen, indicating pockets of permanent deformation in the EPS foam. Surprisingly, even after the tenth impact, the helmets still retained some protective capability. This suggests that using a helmet that has sustained prior loading is still better than not wearing a helmet at all.