Abstract
The structural behaviour and deformation mechanisms of the shells of motorcycle helmets in impacts have been studied. The localised bending of the shell was measured by a set of accelerometers, and the values related to force on the striker. Thermoplastic helmet shells are less stiff than composite ones and they rebound more. When a fibre reinforced shell hits a flat surface the shell deformation is small, and 75% of the foam liner deformation occurs by the rigid headform compressing the inside of the liner. A deformable skull would not compress the foam in the same way, so national test standards may have led to inappropriate helmet designs.