Research On The Protective Performance Of Different Helmets Against Head Injury On Landing In Electric Two-wheeler(ETW)collision Accidents

Under the background of"double carbon"and the rapid development of the express delivery and takeaway industries,electric two-wheelers have become one of the most important means of transportation for people to travel because of their short-distance convenience.However,electric two-wheeler riders,as vulnerable groups on the road,are also extremely vulnerable.According to the statistics of the 2020 Annual Conference of China Traffic Accident In-depth Study,among the 6,067 traffic accidents in the country,the accidents of second-and third-wheeled vehicles account for 62%.In the China Statistical Yearbook,electric two-wheeler accidents accounted for 10.81%and 11.18%of the total number of road traffic accidents in2019 and 2020,respectively.Helmets are an important equipment to protect the head of riders in electric two-wheeler accidents,and the problems of cyclists not wearing helmets,wearing inferior helmets and wearing irregularities on the road have greatly increased the head injury in accident collisions,so it is of great significance to study the protective performance of different helmets based on the reconstruction of electric two-wheeler accidents.In this paper,a typical electric two-wheeler full-face helmet a and a half-coverage helmet are first modeled with finite element,and then the fall simulation is simulated according to the national standard GB 811-2010 and compared with the actual drop test to verify its effectiveness.The verification is mainly evaluated by the acceleration peak of the head centroid line and the curve trend,and the results show that the acceleration curve fitting effect obtained by simulation and test at each collision point of the two helmets is good,and the error of the full-face helmet is controlled within 8%,and the error of the half-coverage helmet is controlled within 10%.This shows that the two helmet finite element models have good realism and can be used for the study of protective performance in riders’landing collisions.In addition,another typical electric two-wheeler full-face helmet b is used in this paper,which has been verified by the impact energy absorption of regulation ECE R22.05 in previous studies.Secondly,ten electric two-wheeler accidents with clear road surveillance videos were screened for accident reconstruction.Accident reconstruction is mainly divided into three modules:PC-Crash speed reconstruction,MADYMO kinematic reconstruction,and finite element injury reconstruction.After estimating the speed and vehicle type data,quickly build the model in PC-Crash and verify its effectiveness through the initial and final positions.The obtained parameters such as speed are brought into MADYMO,and a multi-rigid body model of vehicle and electric two-wheeled riders is established,and the effectiveness of kinematic reconstruction is verified by continuously benchmarking the kinematics and final position of cyclists during the collision.Among them,the error between the final position of the rider and the vehicle and the actual accident sketch in the PC-Crash and MADYMO reconstruction is controlled within 10%.After that,the posture of the rider in the multibody system when colliding with the ground is extracted,and the boundary conditions in this state are obtained,and the finite element damage reconstruction is substituted into the LS-DYNA environment.The results showed that many head injury indicators almost all matched the injury level in the hospital casualty report,and the injury reconstruction was effective.Finally,two full-face helmets and one half-coverage helmet were loaded onto the finite element model of the human body to study the protection of different helmets against skull fractures and brain injuries in riders.When the rider’s head is subjected to a small linear shock load,all three helmets can significantly reduce the risk of skull fracture by more than 70%,and there is no significant difference in the protective effect.In case C4,where the frontal bone first collides with the ground,the brim of the half-coverage helmet is subjected to the impact force of the ground,causing the radial grounded foam to shift,and the foam is bottomed prematurely,resulting in its protection against skull fractures being significantly lower than that of the two full-face helmets.In terms of brain damage caused by rotating loads,almost all three helmets can reduce angular acceleration.Both full-face helmets have the largest diagonal acceleration reduction in Case C7 and the smallest in Case C2,which have structural similarities.For the maximum main strain of the brain,CSDM_0.15,and shear stress,the protection effect of all three helmets is not ideal:the average drop ratio of the half-coverage helmet is less than 20%,and the average drop ratio of the two full-face helmets is less than 30%.In contrast,the three helmets had the most significant reduction in positive intracranial pressure,with each reduced by more than 65%.In addition,the results of the DAI assessment based on CSDM_0.25 show that half-coverage helmets are less effective in protecting against DAI,while full-face helmets have a better advantage in reducing the risk of DAI.Combined with a number of indicators,the protective effect of the full-face helmet on brain damage is better than that of the half-coverage helmet.