Passive Pedestrian Protection Approach for Vehicle Hoods

Global regulations intended to enhance pedestrian protection in a vehicle collision, thereby reducing the severity of pedestrian injuries, are presenting significant challenges to vehicle designers. Vehicle hoods, for example, must absorb a significant amount of energy over a small area while precluding impact with a hard engine compartment component. In this paper, a simple passive approach for pedestrian protection is introduced in which thin metal alloy sheets are bent to follow a C-shaped cross-sectional profile thereby giving them energy absorbing capacity during impact when affixed to the underside of a hood. Materials considered were aluminum (6111-T4, 5182-O) and magnesium (AZ31-O, AZ61-O, ZEK100) alloys. To evaluate the material effect on the head injury criterion (HIC) score without a hood, each C-channel absorber was crushed in a drop tower test using a small dart. Two high speed cameras captured dart image data before and during impact from which HIC scores were computed with stereo digital image correlation (DIC). The only absorber material that fractured during impact, Mg AZ31-O, had the lowest and hence most favorable HIC score relative to those materials that crushed without fracturing. Test results were then compared with predictions from finite element (FE) simulations of the dart impact tests for Mg AZ31-O and Al 5182-O. Good correlation between the tests and simulations was achieved indicating that FE simulations can reliably be used in material selection and design optimization of energy absorbers as passive means for pedestrian protection.