| Human head is the most vulnerable in road traffic accidents involving motorcyclists where the helmet is commonly used to protect human head and reduce head injuries.However,head injuries still happen widely in road accidents even though wearing a motorcycle helmet.Therefore,there is a need to enhance the protection performance of helmets to further reduce head injuries.According to reported literatures,helmet energy-absorbing liner is designed to absorb most of the impact energy,the conventional energy-absorbing liner which is made of a uniform-density polymer foam cannot fully gain advantage on helmet's protection improvement.It would be significant option to improve the energy-absorbing capacity of the liner to further enhance helmet's impact protection.This study aims to develop a methodology for the analysis of a novel motorcycle helmet,investigate the head injury mechanisms and helmet's protection performance during impact scenarios through the experimental,numerical and optimization methods.The main contents were summarized as follows.(1)Development and validation of motorcycle helmet-head FE model.The representative full-face motorcycle helmet was selected to obtain the helmet's geometric model,which was obtained by 3D scanning and geometric reverse reconstruction.Based on the geometric model,the helmet FE model was established.The drop test simulation was conducted through the rigid head FE model coupled helmet model.According to the helmet standard ECE R22.05,helmet drop tests were carried out to output the acceleration transmitted to center of gravity of head.Finally,the helmeted head FE models were validated by the experimental results.(2)Analysis of head injury and protective performance of functionally graded bionic helmet.Functionally graded foam was introduced in this study to replace the uniform-density energy-absorbing liner of conventional motorcycle helmet for improving its protection performance and further reducing head injuries during impact scenarios.The helmet model coupled with biomechanical head model were developed,the acceleration transmitted to the center of gravity of head,biomechanical responses of head and crushing behaviors of helmet under the impacts were obtained to comprehensively investigate the effects of functionally graded foam on helmet impact protection.According to the results,functionally graded foam has more advantages under medium/high speed impact than uniform liner foam.In comparison with the uniform-density design for the conventional helmet liner and the positive/negative functionally graded foam design for the novel helmet liner,the negative functionally graded foam with maximum density of 80 kg/m~3 is of the best crushing responses and the severities of head injuries can be reduced more effectively.With the increase of density difference,the impact protection of novel helmet with negative functionally graded foam design can be further improved.(3)Impact analysis and optimization study of a honeycomb-filled motorcycle helmet.Analyses and discrete optimization design were conducted to investigate the use of honeycomb filler in helmets to further improve their protective performance under impact of kerbstone anvil.Based on the validated honeycomb model under out-of-plane compression,the honeycomb-filled helmet model of kerbstone anvil was established.The protective profermance of honeycomb-filled helmet model under kerbstone anvil and flat anvil was analysis,and the effect of honeycomb structure parameters on protective performance of helmet was explored.It was found that honeycomb filled helmet of kerbstone anvil is more safety than flat anvil,and the honeycomb with more lower thickness and higher length can help in the protection improvement of helmet.An optimization study was implemented to find the feasibly optimal geometries of honeycomb filler and densities of liner foam for the helmet under impact of kerbstone anvil,which can significantly enhance helmet's protection performance and reduce head injury from impact scenarios. |
PDF Full Text Request