Oblique impact testing of bicycle helmets

Accident analysis showsthat the majority of bicycle helmet impacts are oblique to a surface, with the most common impact sites at the front and sides of the head. Hodgson showed that high frictional forces could occur when no-shell bicycle helmets made oblique impacts on rough concrete surfaces, while McIntosh et al. noted that some no-shell helmets fractured into several pieces in crashes. Consequently, current helmets all have an external shell. This paper describes bicycle helmet performance in oblique impact tests; a parallel paper uses some results to validate finite element analysis (FEA) of the tests. In return, FEA can interpret experimental events, reveal causative mechanisms, and allow the evaluation of interface frictional conditions. The performance of bicycle helmets was investigated in oblique impacts with a simulated road surface. The linear and rotational accelerations of a headform, fitted with a compliant scalp and a wig, were measured. The peak rotational accelerations, the order of 5 krad s-2 when the tangential velocity component was 4 m s-1, were only slightly greater than in comparable direct impact tests. Oblique impact tests were possible on the front lower edge of the helmet, a site commonly struck in crashes, without the headform striking the [`]road'. Data characterizing the frictional response at the road/shell and helmet/head interfaces, were generated for interpretation via FEA modelling.