Facial impacts to crashed motorcyclists and full-face helmet protection
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NO FULL TEXT AVAILABLE. This thesis contains 3rd party copyright material. ----- The effectiveness of motorcycle helmets in reducing the risk of head injury and death in a crash is undeniable, but helmet protection is not perfect. One area of helmet design able to achieve safety gains is improved facial impact protection of full-face helmets. The helmet facial region is frequently damaged in crashes, and facial impacts are more regularly injurious than impacts elsewhere on the helmet. Many current motorcycle helmet standards do not have an impact energy attenuation requirement for the face of full-face helmets. Optimum helmet characteristics for facial impact protection are not known. This thesis investigates full-face motorcycle helmet design for head and neck injury risk reduction in facial impacts. The suitability of the chin bar drop test currently used for full-face motorcycle helmet assessment in the European regulation (UNECE 22.05) is evaluated. In order to test under conditions relevant to real riders, in-depth motorcycle crash investigations were analysed to define injurious facial impact conditions, and head and neck injury types sustained by full-face helmet protected riders. A test method applying a radially directed impact to the central chin bar and visor of a helmeted human surrogate, incorporating biofidelic head and neck response with multiple injury criteria, was developed. Physical testing confirmed that full-face helmets, with and without crushable foam padding in the chin bar, can reduce brain injury risk in facial impacts compared to an unhelmeted rider. A finite element (FE) full-face motorcycle helmet model was developed through physical testing of a commercially available helmet and its components. Chin bar drop test simulations showed that the helmet shell, loaded by the headform through the chinstrap, provided a significantly greater contribution to energy attenuation than in impacts to the main cranial portion of the helmet. Injuries observed in the crash studies were predicted in simulated helmet-protected facial impacts using an FE human body model. In comparison to the validated FE helmet model, increased chin bar shell stiffness predicted more favourable head injury mitigation outcomes. The presence of chin bar foam, and ensuring a tightly fastened chinstrap, were major factors in preventing facial and skull fractures. Chin bar shell and foam padding characteristics that performed well in the UNECE 22.05 chin bar drop test also performed well in providing a head injury risk reduction when tested with the biofidelic test method developed here. A modified UNECE 22.05 chin bar drop test is appropriate for inclusion in other motorcycle helmet standards.
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