Bhattacharjee, S., Mane, S., Kusnoorkar, H., Hwang, S. et al., "Pedestrian Head Impact Time Estimate based on Vehicle Geometric Parameters," SAE Technical Paper 2017-01-1453, 2017, doi:10.4271/2017-01-1453.
Pedestrian protection assessment methods require multiple head impact tests on a vehicle’s hood and other front end parts. Hood surfaces are often lifted up by using pyrotechnic devices to create more deformation space prior to pedestrian head impact. Assessment methods for vehicles equipped with pyrotechnic devices must also validate that the hood deployment occurs prior to head impact event. Estimation of pedestrian head impact time, thus, becomes a critical requirement for performance validation of deployable hood systems. In absence of standardized physical pedestrian models, Euro NCAP recommends a list of virtual pedestrian models that could be used by vehicle manufacturers, with vehicle FEA (Finite Element Analysis) models, to predict the potential head impact time along the vehicle front end profile. FEA simulated contact time is used as target for performance validation of sensor and pyrotechnic deployable systems. While the current FEA-based process is a reasonable one, it can be further simplified by defining the expected contact time as a function of geometric parameters of a vehicle’s front end profile. In fact, this proposed simplified method is an extension of the current global pedestrian impact assessment methods, where vehicle geometric parameters are used to define target impact zones, impactor types and impactor energy. The objective of this paper is to present an empirical relationship defining the pedestrian head impact time as a function of vehicle geometric parameters. This proposal has been developed based on a preliminary study of three in-production vehicles with significant variations in front-end geometry and stiffness properties - a sedan, a mid-size SUV and a pick-up truck. Vehicle impact simulations have been conducted with 6 year old child, 5th%tile female, 50th%tile male and 95th%tile male FEA pedestrian human models. The intention of this paper is to encourage further research on the development of a robust empirical formulation for the prediction of pedestrian head impact time based on vehicle geometric parameters. This simplified method can be eventually included in pedestrian test protocols for GTR compliance and NCAP performance rating.