Protection of the unhelmeted head against blunt impact: The pedestrian and the car bonnet

Protection of the unhelmeted head against blunt impact T. P. Hutchinson, D. J. Searson, R. W. G. Anderson, J. K. Dutschke Centre for Automotive Safety Research, University of Adelaide In recent years, increasing attention has been paid to improving car frontal design in order to minimise pedestrian injury. Many tests have been carried out using a free-flight instrumented headform projected against the car exterior. For pedestrians and other vulnerable road users, the bonnet should be thought of as a cushion. General principles of bonnet design can now be stated. There is likely to be quick progress in coming years as bonnet designs are revised: in many respects, testing protocols for regulatory and consumer information purposes will work well. However, in the case of bonnet stiffness, there is an optimum: too stiff, and the bonnet is injurious; not stiff enough, and the pedestrian’s head may bottom out, i.e., strike the very stiff structures in the engine compartment. Furthermore, the optimum bonnet stiffness will be different for different speeds of impact. This suggests the need for testing over the whole range of speeds at which serious pedestrian injuries occur. Theory does permit scaling of HIC (Head Injury Criterion) to different speeds, however, so not all speeds will need to be tested. Scaling will not be valid to speeds where bottoming out occurs. A very important gap in knowledge concerns mild bottoming out: how can HIC be predicted, and what design changes can be made to minimise the increase in HIC?