Influence Of Neck On Head Dynamic Response And Brain Injuries In Car To Pedestrian Collisions

In the field of vehicle safety design，one of the test methods for assessment of theperformance of the passenger vehicles for pedestrian head protection has been madeby use of free-flight headform impactor. The test considers impact orientation andimpact speed as the inputs. The HIC merely treats the resultant translationalacceleration and the duration of the impulse. However，the influence of the headboundary conditions at neck level are significant for injury severity, especially forhead–brain injuries.The primary objective of this thesis was to study the influence of neck on headkinematics and head-brain injuries during car-to-pedestrian impact based on realaccident reconstruction.Firstly,6real-world car-to-pedestrian accidents for different vehicle speeds andvehicle types were reconstructed using Madymo multi-body dynamic program and the50th percentile human model. Secondly, in order to investigate a possible dependencyof the forces and torques between the head and the neck, the results from6accidentreconstructions have been analyzed. In addition, two configurations of the pedestrianhead impact are studied in terms of an isolated head model and a whole body model,based on the reconstructions. The configuration of the isolated head model wasobtained by removing upper-neck joint5ms before head impact. The effect of eachconfiguration on head kinematics responses parameters were computed，includinglinear and angular accelerations，and HIC. Thirdly, biomechanically representativefinite element head with and without neck models were used to compute the physicalparameters related to head-brain injuries. The initial impact conditions of FE modelswere obtained from Madymo reconstructions.The maximum head linear accelerations from simulations indicated that there is40%differences between the accelerations calculated with or without neck force had.The differences of the peak angular accelerations ranged from-30%to28%. Thedifferences of HIC values ranged from40%to127%. For coup/countrecoup pressure,the differences were-5%~10%and-10%~15%, respectively. For the von Mises andmaximum shear stresses of the brain, the differences were basically within a range ofthe-34%~30%. According to the results from this study, a dependency between hea d and neckwas determined. The reasons are on the one hand the high forces/moments in the neck(high coupling) and on the other hand the possible influence of the neck on maxlinear/angular acceleration and HIC. Furthermore, the value of the neck loadingdepends on the vehicle front. The isolated head model has higher peak linearacceleration and HIC than that from the whole body model. The influence of the neckon the peak head angular acceleration was significant. It appeared that the values offour injury parameters from head-with-neck model differed from that calculated withhead-without-neck model because of different head boundary conditions at neck level.The head-brain injuries parameters were calculated in terms of coup/countrecouppressure, von Mises and maximum shear stresses. The results from this research canbe used for pedestrian head protection and improvement of the current headformimpactor.