Study On Optimization Of Automobile Bumper’s Performance Based On Low Speed Impact And Pedestrian Protection

According to the traffic data, pedestrians are the main victims in traffic accidents, so countries have promulgated the pedestrian protection regulation to improve pedestrian protection function of automobile. When the pedestrian and vehicle collision occurs, the pedestrian leg is the mainly injured part. Besides, the bumper is the first part that impacts the pedestrian leg, thus reducing the overall stiffness of the bumper system is beneficial to reduce the pedestrian’s leg injury. However, the bumper system also plays a key role in low-speed collisions,that’s to protect radiator and occupant inside the vehicle, the reduction of the overall stiffness of the bumper system is not conducive to the low speed crashworthiness. Therefore,this dissertation carried out the optimization design of the bumper structure based on the low speed crashworthiness and pedestrian leg protection of the bumper system.First of all,this dissertation did a thorough understanding on the pedestrian protection regulations and low speed impact evaluation system among countries. And pedestrian protection followed the European new car assessment program (EuroNCAP), low-speed vehicle collision referred to ECE R42. Then this dissertation established the finite element model of automobile collision at low speed and vehicle pedestrian leg to carry out the simulation calculation, in which the output response of low speed collision was intrusion displacement of bumper beam, the output response of the pedestrian leg were tibia acceleration, knee bending angle and knee shear displacement of the joint, to evaluate the model of this dissertation whether meets the EuroNCAP and ECE R42. Due to the error of finite element analysis, considering10%of the margin of safety, pedestrian tibia acceleration was beyond the Euro NCAP target values after considering the safety margin. Therefore, this dissertation made the thickness of the beam, thickness of the fascia and the energy absorbing foam density as design variables, with the tibia acceleration as the optimization objective,the knee bending angle,knee shear displacement and the penetration displacement of bumper beam as constraint response. Furthermore, deterministic optimization of bumper structure was carried out by adopting experiment design,modeling and Multi-Island genetic algorithm. Finally, considering the uncertainties of the design variables, robustness optimization design of the bumper structure was carried out by using6-Sigma quality design based on Monte Carlo simulation. The results of this study showed that, despite the robust optimization results and the deterministic optimization results have small difference in value, the robust optimization results compared to the initial design in value has been greatly improved. Furthermore, the reliable robustness of robust optimization results was improved greatly than the deterministic optimization results, so as to meet the design requirements.