Research On Head And Lower Extremity Injury Mechanisms Based On A Six-year-old Child Pedestrian Finite Element Model

Road traffic accidents have become one of the important factors threatening human life safety.Compared with adults,children are more vulnerable on the road because of both their incomplete physical development and limited social cognitions.Due to various factors,there have been relatively few studies on pedestrian injuries in children.Therefore,it is necessary to study the effects of gait and impact direction on head and lower limb kinematics and injury responses of six-years-old child pedestrian by establishing simulation experiments with different gait states and impact directions by using finite element methodBased on the six-year-old child pedestrian standing posture finite element model developed by the laboratory,this paper adjusted the six-year-old child pedestrian standing posture model according to the Euro NCAP standard for six-year-old pedestrian walking posture model.Six-year-old child pedestrian finite element models with two gaits were used to simulate pedestrian-car side impact and the similarities and differences of head and lower limb motion and injury are compared.The result indicated a significant difference between the shoulder and head hitting the hood and the movement of the lower extremities.The initial speed of the head striking the hood was less than the initial speed of the vehicle which was 11m/s.The facial bone injury in walking posture pedestrian was higher than that in standing posture but the risk of skull fracture or brain injury of standing posture wer higher than that of walking posture.There was no difference in the injury of the pelvis.The knee joint injury on one side of femoral fracture was less than that on the side of no femoral fracture,and the meniscus injury risk on the collision side was significantly higher in walking position than in standing position.For the tibia,the left tibia(impact side)in standing posture was at the greatest risk of injury while the right-fibula was at the greatest risk of injury under walking posture for the fibula.The pedestrian car impact simulation experiments were carried out with four kinds of impact direction.The results indicated that there was a significant difference in pedestrian motion among the four collision angles,resulting in a difference of about 10ms between HIT values under 0° and 180° impact and those under 90°impact and 270° impact;the initial collision speed of head impacting hood under both 0° and 180° impact was less than the initial collision speed of vehicle;and it was opposite for 90° and 270° impact.In addition,the degree of facial bone injury in 90° and270° collisions were much higher than that in 0°and 180° collisions and the risk of skull and brain contusion were highest in 270° collisions.The risk positions of femoral fracture and pelvic fracture were different,and ligament injury was also different.The knee meniscus on the collision side is at high risk of injury;the maximum stress of tibia in the flexion state was greater than that in the tensile state;the tibia and fibula with the greatest risk of injury were located in the lower limbs of the 270° impact.The results indicated that gait state and impact direction had great influence on pedestrian kinematics and head and lower limb injuries of six-year-old child pedestrian.The results can provide theoretical reference to further studies on pedestrian injury mechanism of six-year-old child pedestrian and development of pedestrian protective devices for child pedestrian.