Pre-stretch-induced Structural Unit For Energy-absorption Application In Improving Bus Structural Crashworthiness In Upside Down Turnover

Buses,as a form of highway passenger transport with large capacity of passengers,its collision safety cannot be ignored.One of the most serious types of bus accidents is the overturning accident,especially when it lands upside down.Once it happens,will lead to mass casualties and injuries.While,because of the heavy-weight bus body and the insufficient strength of the bus upper structure,it is difficult to provide enough structural protection for the passengers.Besides,the researches on upside down bus turnover accidents as well as the relevant regulations and testing requirements are still insufficient.Under mentioned background,this paper puts forward a pre-stretch-induced structural unit which using stretching energy to absorb the impact energy.After full verification of its stiffness,modal and impact energy-absorbing properties,its characteristics are applied to an integral bus with steel-aluminium mixtures structure.By comparing with the original bus,it is proved that its structural performance and impact energy-absorbing performance have been significantly improved,and the integrality of passenger living space can be effectively guaranteed in upside down bus overturn accident.Firstly,by analyzing some upside down bus overturning accident,the characteristics and factors of bus overturning accident are summarized.Then,the relevant regulations as well as the research status of bus collision safety and vehicle rollover safety are introduced.By theoretica and experimental analyses of the energy absorption by compression of the crash box,it is proved that the energy absorption by material stretching has the advantages of high specific energy absorption and stability under force.So,the scheme of using material stretching to absorb energy is determined below.Then,this paper proposes a pre-stretch-induced structural unit which uses stretching energy of rods to absorb the impact energy,and compares it with a cuboid structure which simulates the traditional bus structure by the aspects of stress,impact acceleration and energy variation of each component,and proves the advantages of the new structure element.Then,a full factorial experiments on the thickness of beams and columns of thestretch-energy-absorption structural unit are carried out to analyze the relationship between the thickness of the frame and the energy absorption performance.The lightweight and energy absorption performance of structural unit are further improved,which lays a foundation for the application on the bus structure.Furthermore,by applying the characteristics of the stretch-energy-absorption structural unit to the structure of an integral bus body,a rollover safety bus structure using stretching to absorb energy is constructed.By comparing with the original bus,it is proved that the stiffness and modal performance of the new structure bus are improved,and the intrusion of the roof can be effectively reduced in the simulation of upside down overturning roof crash test to ensure that the passenger living space will be well preserved.Finally,the rules between the thickness of the energy absorber rod and the energy absorption performance of the bus structure are studied,and the influence of the thickness of the energy absorber rod on the structure is clarified.The structure provides important engineering reference value for improving the collision safety of bus body in the future.