A Study On Head Dynamic Responses And Injury Mechanisms In Pedestrian And Cyclist Traffic Accidents

Pedestrians and cyclists are the most vulnerable road users (VRUs) in traffic accidents. The number of annual fatality from traffic accidents in China is about 100 thousands, of which the outside umprotected road users, such as pedestrians, motorcyclists and bicyclists, account for 60%. Head injury is the one of the most popular traffic injuries, which makes up a proportion of 22.5-41% of the total injuries. Head injuries are the main cause of fatality. Hence, it is crucial to conduct research on head injury pattern, injury mechanisms, injury tolerance, and protective measures in China.A total of 50 pedestrian and cyclist cases were reconstructed based on in-depth accident investigation by using multi-body dynamic softwares PC-Crash and MADYMO. Human dynamic responses during collisions were precisely reoccurred, and the injury criterion indices calculated from these reconstructions were compared with diagnosis reports. Comparison studies on head dynamic responses and injury risks in car-to-pedestrian collisions in Changsha and Hannover were conducted. It is shown that the two areas share almost the same car from structure. The average height and weight of victim pedestrians of Hannvoer is about 7.7cm higher and 10.3kg heavier than that of Changsha area, which could cause the distinguishes on head contact time and wrap around distance (WAD). The average head impact velocity and angle of both areas are similar as the regulation of EEVC subsystem tests:40km/h and 50°for adult pedestrian protection. There is little difference for the two areas in the view of car-to-pedestrian safety improvements. Therefore, it is acceptable for Chnia to follow the EU test codes for pedestrian safety.In order to understand the differences of load and impact conditions for head injuries between car-to-pedestrian and car-to-cyclist accidents, comparable analysis of the exact impact configuration and the resulting injury patterns as well as assessment of head injury risks and kinematics in primary and secondary impacts were performed. Physical parameters like HIC value,3ms linear acceleration were correlated to head injury risks by employing logistic regression method. In point of traffic epidemiology, there are comparabilities in vehicle type, crash configuration, and cause of injury distribution and so on in pedestrian and cyclist accidents. Nevertheless, abvious differeces exist in vehicle impact velocity, injury severity and injury distribution. In the view of head dynamic response from the result of accident reconstruction, pedestrians and bicyclists differ obviously in average gravity height, head impact velocity, head displacement, thrown distance and landing type. The research results give the answers for directives currently applied to vehicle design for pedestrian to a large extent cover the requirements for protection of cyclist.Using HBM head finite element model, identical impact and boundary conditions were defined in the simulation of frontal and lateral head impacts, physical injury parameters such as intracranial pressure, von Mises stress and shear stress predicted from theses impacts were analyzed. The results from comparison study illustrate that the head injuries resulted from skull deformation, skull von Mises, brain tissue von Mises and maximum sheare stress of lateral head impact could be more severer than that from frontal head impact. The maximum positive and negative intracranial both appear at cerebrum. The intracranial propagation mode of impact wave from frontal and lateral head impact varied obviously. The magnitude of maximum intrecranial negative pressure from lateral impact was 23% higher than that predicted for frontal impact, but the maximum negative pressure at contre-coup side calculated from lateral impact was 59% lower than that observed in frontal case.From the 50 reconstructed cases,30 head-to-windscreen cases were selected for head injury reconstruction, the effects of coup and contrecoup intracranial pressure on cerebrum, cerebellum, callosum and brain stem injury risks were analyzed. Logistic regression models between predicted parameters and injury severity risks were created. Relationship between contact force and skull fracture was investigated. Different brain injury responses between concentrated and distribution forces were identified. The results from brain injury reconstruction indicate that 83% coup site and 73% contrcoup site peak intracranial pressure occurred at cerebrum and callosum. The positive pressures at cerebrum, callosum, cerebellum and brain stem predicted for 50% possibility of AIS3+ head injury occurance were 239kPa,178kPa,201kPa and 182kPa,and the corresponding negetive pessures were-156kPa,-138kPa,-140kPa,-160kPa respectively. The predicted peak pressures at coup site and contrecoup site obtainded from distributed load decreased 49% and 51% respectively compared to concentrated load, however, when comparing the peak values of shear stress and von Mises stress, the magnitudes from distributed load increased to some extent based on the calculated data of concentrated load.According to child pedestrian head protection regulation provided by EEVC, a comparison of steel and aluminum hood with the same traditional structure was studied in the view of pedestrian protection. Child-pedestrian friendly as well as comparable static stiffness bonnet designs:sandwich structure hood, multi-cone and wavilness inner panel hoods with aluminum alloy were proposed and evaluated in this study. An investigation of adding absorbers between hood-side-edges and wings to increase energy absorption and optimize acceleration curve was carried out.The car front structure, especially the width of bumper and the angle of bonnet, influenced the chid pedestrian head injury more significantly than that of adult pedestrians. Traditional reinforced inner hood was aggressive to child pedestrian head. In aspects of stiffness and energy absorbtion, concepts of sandwich structure hood, multi-cone and wavilness inner panel hoods with aluminum alloy were proposed to satisfy the requirements of child head protection advanced by EEVC. Adding crushable absorbers between hood-side-edges and wings can increase energy absorption and optimize acceleration curve in these test zones.China's auto output and distribution have been arranging the first place globally. In traffic accidents, the traffic injury prevention and treatment for vulnerable road users (Pestrians and cyclists) are turning into the focal problems. Based on accident investigation and analysis, the dynamic resoponses of pedestrian and cyclist to vehicle collisions were studied. According to accident analysis results, in-depth researches on head injury mechanisms were performed by using finite element head model. The results of current study have important practical meaning in developments of vehicle safety and the prevention of traffic injuries.