Parameter Optimisation Of Vehicle Front-end Structures For Pedestrian Head Protection

With the development of the automobile industry,the problem of the traffic accident and pedestrian protection have been more and more concerned.A series of laws and evaluation methods for the pedestrian protection have been made.The statistical analysis of traffic accidents happened at Weihai from 2011 to 2014 indicate that in the process of vehicle-pedestrian collision,the pedestrian head is easy to collide with the vehicle front-end structures such as the windshield and engine hood,and that could bring the pedestrian the risk of maximum abbreviated injury scale(MAIS)3+ and fatality.Hence,to research on the optimization of windshield and hood will be useful to reduce the pedestrian head injuries caused by vehicle front-end structures in pedestrian accidents.In order to carry out experimental research on pedestrian injuries attributable to the vehicle front-end structures,a headform-vehicle impacting system is built which can test instantaneous state of vehicle front-end structures.An adult headform impactor is designed and trial-produced according to the national standard.The headform impactor is validated through the drop tests.Using the headform impactor,a headform-windshield impact system is set up,which is composed of head lifting/falling system,data acquisition system and image acquisition system.Using this experimental system,a seris of impacting tests are carried out to investigate the head injuries,including impacting on different positions,on windshields with different PVB thickness,on windshields with explosion-proof membrane,and imacting with the wigged headform.The crack propagation and crack distribution in the process of impact is explained based on the propagation rules of stress wave in laminated medium.Combined the movement and acceleration of headform,with the crack propagation of the glass,the headform-windshield impact process is analyzed comprehensively.In consideration of the fatal head injuries resulted from the windshield,the finite element model(FEM)of windshield is studied and the parameter optimization is carried out for pedestrian head protection.The FEM of windshield is established in three ways: single-layer,double-layers and three-layers.The three-layers FEM comprised of solid elements is confirmed to be the best according to the test results.Using this FEM,the pedestrian head injuries caused by windshield with different curvatures and different laminated structures were analyzed.Based on the Hyper Kriging approximation models,using the Adaptive Response Surface Methodology(ARSM),the impacts of dimension or material parameters of windshield on pedestrian head injury were analyzed respectively.Based on the Kriging approximation model,comprehensive optimization of windshield was conducted using the algorithm of ARSM and feasible direction method.The comparison of the optimization methods provides a useful reference to the comprehensive optimization of sensitive parameters of windshield.In order to reduce the pedestrian head injury induced by engine hood in pedestrian accidents,material design and parapmeter optimization of engine hood are researched.Because of the insufficient of buffer space between the hood and the parts(hard spot)in engine cabin,the secondary collision is likely to happen between the pedestrian head and the hard spot or the support may be changed due to the contact of hood and hard spot.Therefore,a complete vehicle FEM is used to simulate the headform-hood impact.An aluminum foam sandwiched(AFS)engine hood is designed for the pedestrian head protection and vehicle lightweight.The simulation results show that the sanwiched hood can significantly reduce the head injury criterion(HIC).To abtain the optimal parameter combination of sanwiched hood,the global and local combinatorial optimizaiton is carried out: based on the optimal Latin hypercube experimental design the approximate model was established with the method of RSM and radial basis functions(RBF),and the engine hood was optimized by NSGA-II and MMFD algorithm respectively.Considering the vehicle’s collision compatibility,the stiffness characteristic of the optimal hood in multi-working condition is analyzed.In order to validate the performance of the pedestrian head protection of vehicle,simulation verification is conducted using the Dodge Neon FEM.The headform impacts with the optimized windshield and the hood respectively.The impact points include the geometric center and the corner of the windshie ld,and the representative test points on the hood.The correctness of the optimization results is analyzed theoretically and the energy absorption properties of the optimized vehicle front-end structures are analyzed.The simulation results show that the optimized windshield and AFS hood could significantly reduce pedestrian head injuries in vehicle-pedestrain accident,which indicates the reliability of the optimization results and the feasibility of the optimization methods as well.