The effect of bull bars on head impact kinematics in pedestrian crashes

Abstract

This study sought to assess the effect of bull bars on the head kinematics and head impact severity of an adult pedestrian in a collision. Multibody models were created to represent a range of sport-utility vehicles and common bull bar geometries and materials. The contact-impact behaviours of the pedestrian-vehicle interactions were determined from a series of impact tests with the vehicles and the bull bars being modelled. A generalised Hunt-Crossley damping model was fitted to the test data. The interaction models were implemented in MADYMO models of a vehicle pedestrian collision using the geometry of the vehicles and bull bars and a fiftieth percentile male human model. Head kinematics were extracted and the head impact severity estimated. The speed of the head impact with the bonnet was increased by between 7 and 55 percent in simulations where a bull bar was fitted to the vehicle. The increase in head impact velocity was not related to the bull bar material type. The 55 percent increase in head impact speed produced a 249 percent increase in HIC value, using a head-bonnet interaction model based on Australasian NCAP head impact test results. The location of the head impact was affected by the bull bar but the effect was not consistent. The simulation results show that the addition of a bull bar to the front of a vehicle increases the speed of the head impact with the bonnet. This speed increase appears to be less a product of the material the bull bar is made from, but more a product of the geometry of the bull bar. This suggests that bull bar geometries could be altered to improve pedestrian collision kinematics possibly even lessening the severity of the head impact with the bonnet. Combined with a soft material, such as polymer, this may lead to a safer bull bar designs for pedestrians.