Influencing Factors of Contact Force Distribution in Pedestrian Upper Legform Impact with Vehicle Front-End

Pedestrian upper leg impact protection is a challenging requirement in the Euro NCAP assessment. In upper legform to bonnet leading edge tests, the legform impact force, the legform intrusion and the injury parameters (impact force and bending moment measured on the upper legform) are highly related to design of vehicle front-end styling and structure, as well as clearance underneath bonnet leading edge. In the course of impact, the contact area variation has significant influence on the stress distribution and consequently the force and the bending moment on the upper legform. Using finite element simulations of upper legform impact with a typical sedan, the deformation of the legform and the vehicle structure, and the variation of the contact force distribution are characterized and analyzed. Based on the study, a method for calculating the contact force is put forward by assuming a shape of the contact zone on the upper legform and a stress distribution function within the contact zone. The calculation method is verified using a simplified model of vehicle front-end structure developed in a previous study. Then a parametric study is conducted using the simplified vehicle front-end model to study influence of key design variables. The results of the parametric study, to some extent, have revealed relationship among vehicle front-end design parameters such as styling, geometry and stiffness, contact characteristics such as the maximum stress on outer foam, and the injury parameters (mainly the impact force).