Car Bonnet Evaluation against Pedestrian Head Impact Based on a Lumped Modeling Approach

Nowadays, physical models of head used in pedestrian head impact standard tests are not accurate enough to represent the human head behavior and to assess the head injury risk in case of impact in a realistic way. In order to remove this technological barrier, the Strasbourg University Finite Elements Head Model (SUFEHM) is used in conjunction with a lumped model of the impact point at bonnet level in the present study. The approach consists in proposing a lumped model of the bonnet based on the experimental response of a pedestrian ISO headform impacting the bonnet surface at a velocity of 11 m/s and an impact angle of 60°. During this experimental tangential headform impact, both linear and rotational headform acceleration are recorded, and these data allow to characterize the stiffness, plasticity, energy dissiparion as well as apparent mass of the bonnet lumped model. The model of the impact point at bonnet level consists of a rigid plate representing the bonnet impacted surface and connected to a fixed point by a general non linear spring. The non linear stiffnesse were implemented to the bonnet model in normal and tangential direction in terms of force-displacement. For this approach, the force was obtained by multiplying the acceleration by the headform mass and the displacement was derived from double integration of the headform acceleration. As a demonstrator the approach was conducted numerically on a car bonnet FEM which was impacted by an ISO headform FEM. The validation of the method consists in simulating the impact of the finite element model of the headform-bonnet lumped model and comparing its response to the headform FEM impact againstthe complete bonnet FEM simulation in terms of resultant linear and rotational acceleration. In a last step the SUFEHM is used for the simulation of the impact against the above defined bonnet lumped model in order to assess the injury risk for the impact point under study.