The Optimization Of Vehicle Front-end Structure Based On Pedestrian Protection

In recent years,the car ownership in China continued to grow rapidly,besides this,China has dense urban population and the urban traffic facilities are not perfect,all of these have result in frequent increasingly road traffic accident,especially for the condition like pedestrians and vehicles mixed collision.When pedestrians collide with a car,pedestrian legs will be in direct contact with the car front-end structure,and it is the injury site of highest risk.Therefore,it is necessary and urgent to study the front-end structure of the car based on pedestrian legs protection.So,the selected topic of thesis has important value in theory and practice.Firstly,in the pre-processing software Hypermesh,a finite element collision model of a car and pedestrian leg was established,and LS DYNA software was used to solve the calculation.In this model,the accuracy of related settings was verified by the analysis of the results based on the analysis of mass scaling and energy.In order to shorten the calculation time,the vehicle model was simplified,and its accuracy of was verified by the vehicle damage value comparison with the vehicle model.The calculation results showed that the pedestrian legs protection performance of the front-end structure of the car is poor and in need of optimization.Then,the foam was used in the front-end structure of the vehicle as the buffer energy absorbing structure.Based on the analysis and calculation of EPP foam energy-absorption structure of five different foaming capacity,an optimal material for leg protection was selected.On this basis,the effect of the cross-sectional shape of the foam energy-absorption structure on pedestrians’ leg damage value was discussed.However,compared with the original car,it was found that the addition of foam energy-absorption structure can not improve the car’s pedestrian leg protection performance.In addition,the energy-absorption characteristics of the foam energy-absorption structure were analyzed,and this structure’s energy-absorption space in need was estimated.The result showed that the energy absorption efficiency of the foam energy-absorption structure is low,and not suitable for energy absorption in the condition of insufficient energy consumption.Finally,a method of obtaining the normalization coefficient for injury index suitable for the vehicle was proposed,according to the damage of the pedestrian leg caused by the car structure.In order to improve the pedestrian leg protection performance of the front-end structure,a steel thin-walled energy-absorption structure with high energy absorption efficiency was used in the car front-end structure.Based on pedestrian leg protection,the optimal cross-sectional shape of this structure was obtained after optimized.On this basis,the optimization for the match of material and thickness was conducted,in this process,the optimal thickness of the steel thin-walled energy absorbing structure was calculated for 6 kinds of materials.After optimization,the tibial acceleration was reduced by 16.83%,knee bending angle decreased by 2.57%,knee shear displacement increased by 71.17%,pedestrian leg comprehensive injury index decreased by 21.28%,compared with the original vehicle,so that,pedestrian leg protection performance of front-end structure of the car has been greatly improved.And it can be found that steel thin-walled energy-absorption structure has high energy-absorption efficiency,compared with the bubble energy absorption structure,and it can give full play to the energy absorption effect especially for the condition that energy-absorption space is insufficient.