This paper discusses the relationships between design parameters and helmet performance according to several criteria, on the basis of defined impact tests on a set of (approved) crash helmets. Main attention is given to outer and inner shell material properties. The test design of ECE Regulation 22 (-03) is used to assess testhead and anvil responses in frontal (forehead) impact. From these responses helmet behaviour is determined, showing typically different deformation modes between fiber reinforced plastic (FRP) shelled helmets and polycarbonate (PC) shelled helmets. Energy absorption of FRP shelled helmets is predominantly caused by deformation of the inner (foam) shell "from the inside", and the load distribution is determined by the compatibility of inner shell dimensions and headform shape. PC shelled helmets predominantly show deformation "from the outside", and load distribution is determined by the geometry of the object hit as well as the load distribution capacity of inner shell material. FRP shelled helmets show higher maximum load and rate of onset, while force distribution and time duration of the impact are favourable compared to PC shelled helmets. The total energy absorbed by helmet deformation is quite similar for alle helmets tested.
Abstract