Study On Structural Features Of Vehicle Front For Lower Limb Injury Protection Of Chinese Pedestrians

Lower limbs are the most frequently injured parts in vehicle-to-pedestrian collision accidents,which are mainly caused by the impact of the front end of the vehicle.Due to the late start of pedestrian protection research in China,the relevant test standards are mostly formulated with reference to foreign countries’.And the lower limb impactor for pedestrian protection testing is also directly imported from foreign countries,which can not accurately represent the lower extremity real injury risk of Chinese pedestrians in vehicle collisions.Therefore,the vehicle safety design under the existing domestic standards may have a better protection effect on the western human body,but it may not be equally effective for the Chinese.Thus,this paper studies the lower limb injury in vehicle collisions with Chinese fine lower limb model to reveal its real injury risks,then,an isolated lower limb model meeting Chinese anthropometric distribution characteristics is developed and which can represent the real injury risk of lower limbs in collision.Finally,based on this individual model,the research on the structural optimization of the front of the vehicle for Chinese lower limb injury protection is carried out,and the front structural features of the vehicle that are truly safe for Chinese are proposed.Firstly,based on the existing Chinese fine pedestrian lower limb model,the effectiveness of the model is verified through three real vehicle-to-pedestrian collision accidents: multi-rigid body simulation is used to reproduce the pedestrian kinematics in collision to obtain the accurate boundary conditions when the accident occurs,and then finite element simulation is used to show the long bone fracture process and the exact fracture situation.The results show that: the fracture morphology predicted by the model is similar to the actual lower limb in the accident.Combined with the cadaveric test data,the verification results of the bending moment threshold when lower limb fracture occured show that the model used in this paper can predict the risk of lower limb injury in real accident with high probability,and has high biological fidelity.Secondly,based on the above mentioned fine pedestrian lower limb model of Chinese human body,using the loading method of attaching mass to the lower extremity buttock to simulate the inertia effect of the upper body in the collision,this work explores an efficient isolated lower limb model that can replace the use of the whole body for lower extremity injury research.The lower-limb overall dynamic responses and corresponding part injury parameters of the whole body and isolated lower limb models with different buttock loads attached under the impact of four different vehicle front structures were compared,respectively.The results show that: the upper body mass has a significant impact on the risk of lower limb injury,the isolated lower limb with an appropriate buttock loading mass can accurately reflect the dynamic response and injury risk of the human lower limb in collisions,and the model can replace the human body for the subsequent structural optimization research of vehicle front based on pedestrian lower limb injury protection.Finally,a vehicle front structure optimization framework based on the coupling of finite element simulation and genetic algorithm is proposed,and the above individual lower limb model is applied to carry out the research of vehicle front structure optimization for pedestrian lower limb injury protection.The results show that the structure of the lower bumper stiffener and the bonnet leading edge with a smaller depth can provide an approximately plane support from thigh to lower leg in collision to reduce the lateral bending of each part,thus reducing the injury risk.Furthermore,the front-end structure with the lower bumper stiffener about 60 mm above the ankle joint（150 mm）,the upper edge of the bumper absorber about 250 mm higher than the knee joint（690 mm）and the bonnet leading edge about 20 mm above the hip joint（900mm）of the vehicle is very beneficial to the lower limb protection of domestic pedestrians.Based on the research on human lower limb injury protection in China,this paper puts forward the front-end structural features of the vehicle that are truly safe for the Chinese people.From the perspective of engineering design,it provides a theoretical basis and data reference for the future vehicle safety design.