Collision Analysis And Optimization Of Vehicle Front-end Energy-absorbing Structure Based On Flexible Pedestrian Legform

Traffic congestion and the mixed traffic between people and vehicles have greatly increased the probability of pedestrian-car collisions.When pedestrians collide with a car,pedestrian's leg will be in direct contact with the car's front-end structure,and the leg bears the highest risk of injury.In July 2018,China will formally implement the ChinaNew Car Assessment Program(C-NCAP 2018),in which the pedestrian lower extremity protection test and scoring based on a flexible pedestrian legform impactor(FLEX-PLI)is added for the first time.Therefore,it is theoretically and practically worthwhile to carry out pedestrian collision safety research based on FLEX-PLI for the car's front-end structure.The basic structure and regulatory requirements of the FLEX-PLI and the TRL-LFI were compared,and a finite element collision model of a simplified car and pedestrian leg was established,and LS DYNA software was used to solve the calculation.The accuracy of the finite element model of the simplified car was verified through comparison between the simulation and test results based on TRL-LFI.The calculation results showed that the medial collateral ligament based on FLEX-PLI cannot meet the requirements of the C-NCAP(2018),and the upper tibia acceleration and the knee bending angle based on TRL-LFI cannot meet the requirements of the GTR9,and it needs to be optimized accordingly.Then,the energy-absorbing foam was used in the car's front-end structure,and 4 kinds of foams with different cross-sections are optimized based on the leg protection performance.Foam with E-shaped cross-section can effectively improves the pedestrian protection performance based on TRL-LFI,and then optimal E-shaped cross-section parameters satisfying the GTR9 regulations are optimized with the goal of coefficient injury index MSE minimum.The energy-absorbing space estimation algorithm shows that the energy absorbing foam can effectively reduce the tibia acceleration of TRL-LFI in the condition of sufficient energy-absorbing space.Then the effect of 4 kinds of foams with different cross-sections on pedestrian protection performance based on FLEX-PLI are analyzed.The results show that either E-shaped or Doughnut-shaped cross-section foam cannot meet the requirements of C-NCAP(2018),because of limited energy absorption and adjustment of the leg motion posture in the collision process.So other measures need to be taken.In order to overcome the deficiencies of the knee energy-absorbing foam in adjusting the movement posture of FLEX-PLI,a support structure was used in the car's front-end structure.Based on FLEX-PLI,optimal support plate thickness and elongation are optimized by multi-objective genetic algorithm based on response surface.Compared with the original car,the pedestrian leg protection performance of the vehicle was greatly improved,injury indicators of FLEX-PLI all meet the requirements of C-NCAP(2018).So the support structure can effectively improve the pedestrian protection performance based on FLEX-PLI by adjusting the movement posture of FLEX-PLI during the collision process.