Research On Protective Performance Of Electric Two-wheeler (ETW) Helmet Based On In-depth Accident Reconstructions

Nowadays,electric two-wheeler(ETW)has become one of the most important means of transportation for people.However,the ETW accident has also increased year by year.As we all know,vehicle safety regulations can reduce the incidence of road traffic accidents to a certain extent,but they can't provide protection for ETW riders who have been exposed to dangerous situations.More attention was paid to the protection for passengers in the safety design of the vehicle.While the protection for vulnerable road users(VRUs),such as ETW riders outside the vehicle,is extremely limited.According to the World Health Organization(WHO),about 1.35 million people died from traffic accidents in 2016,of which bicyclist and motorcyclist accounted for 3%and 28%respectively.In addition,according to the statistics report of the Ministry of Public Security of the Traffic Management Bureau of China,the death of electric bicycle riders and motorcycle drivers in 2017 was 31447 and 48929 respectively.Since the insufficient protection is provided for ETW drivers in the safety design of the vehicle in the accident,the ETW driver is required to have a protection device to reduce'the head injury caused by the collision accident.The current work was to study the protective performance of ETW helmet and analyzed the possible deficiencies of the helmet.The primary purpose of this work was to study the ability of the helmet to absorb the impact energy of the head when installing different density of the liner foam,and further analyzed the protective performance of the helmet under different liner foam density on the skull fracture.In addition,the three real ETW accidents were reconstructed,recreating the entire kinematic response of the ETW driver colliding with the ground during the collision accident.Finally,the protective performance of the helmet on the skull fracture and brain injury was studied based on the in-depth accident reconstruction.In this study,the finite element model of a composite ETW helmet was modeled,and then the helmet FE model was validated by the impact absorption test according to the regulation EEC R22.05.The validation results showed that the errors of the resultant linear acceleration and HIC were controlled at about 5%and 10%,respectively.Further,a series of helmet drop simulations with a foam density radient of 20kg/m3 were designed,and 12 simulations were carried out for four helmet test points.The results showed that when the density of liner foam increased from 40 kg/m3 to 80 kg/m3,the risk of skull fracture increased from 25%,55%,and 39%to 53%,96%and 96%for test points B,P,and R,respectively.For the test point X_Right,the risk of skull fracture with the liner foam density of 40 kg/m3 was greater than that of risk with the liner foam density 60 kg/m3 since the liner foam compress was closer to the compaction section.This study reconstructed the ETW-to-vehicle impact accident based on the clear and complete collision process recorded by the road monitoring videos.Firstly,multi-body models were built based on the actual size of the vehicle and the ETW in the accident and the specific information of the ETW driver.Then,the speed angle of the vehicle and ETW before the collision were estimated according to the accident video.Finally,the accuracy of the accident reconstruction was validated by the kinematics response of the ETW driver recorded by the video.It could be seen from the results that the kinematic response of the dummy in the simulation was very close to the kinematics of the victim in the actual accident.In addition,the error of the final position of victim and the vehicle was controlled within 10%compared with the actual accident sketch.In this study,the protective performance of the helmet on craniocerebra injury was studied based on the in-depth reconstruction of the real ETW collision accident.In Case 1 and 2,the risk of skull fractures after wearing a helmet was reduced from 100%to 46%and 4%,respectively,while in Case 3 the risk of skull fracture was reduced from 100%to 94%.This indicated that the helmet can provide effective protection against skull fracture under normal impact strength,but it will not be able to protect against skull fractures under severe impact due to the bottoming of the liner foam.However.three accident cases have shown that the helmet has very poor protection against DAI and concussion.