Study On Body Structure Improvement And Occupant Injury For Bus Rollover Safety

Based on the great advantage of low cost and large passenger capacity, busplays a great role on easing traffic congestion as an important urban and intercitypublic transportation tool. Meanwhile, bus accounts for an important proportion inmodern transportation systems. According to the statistic reports published by theTraffic Management Bureau of China Police Ministry in2010, the number of largeand middle bus in China reached2.62million with an average increasing speed of4.5%per year from2004. However, along with the increase of the number of buses,the number of passengers and the speed on the highway, the number of bus accidentswere also increased incessantly. Since the bus carries many passengers, the busaccident can be a serious or an extra serious accident and results many casualties.The types of bus accidents include front crash, side crash, rear crash, guardrail crash,rollover crash and so on. In bus rollover crash, the occupant survival space isintruded by serious deformation of bus body upper structure, which can cause severeinjuries of occupants. Therefore, the safety performance of bus and the protection ofoccupants during a rollover crash have become an important research topic for busmanufacturers.At present, the European regulation ECE R66is a representative regulationregarding to the safety performance of bus during a rollover crash. The strength andstiffness of bus upper structure are required in this regulation, which is important toimprove the safety performance and the occupant protection. At present, the researchat home and abroad related to bus rollover crash safety mainly concentrated on thestrength and stiffness of bus upper structure and the occupant injury according to theECE R66. These researches were carried out more but there are also some problemsexisting must be deeply studied.Based on the massive literature review, this thesis focused on the studies of theimprovement of bus rollover safety，the structure optimization of bus body and theoccupant injury by using experimentation analysis method, finite element analysismethod, multi-body analysis method and optimization design method. The mainresearch and innovative points of this thesis are as follows.1. Improvement of bus rollover safety. According to the bus CAD modelprovided by manufacturer, the finite element model of the bus was developed and theLS-DYNA software was used to simulate the dynamic response during the rollover process. In accordance with existing problems of the original bus body structure, thecountermeasur of tube filling was proposed. In order to achieve the requirements oflight-weighting the bus body and consider the convenience of filling technology, anew filling composite which includes epoxy resin, wood flour and hardening agentwas used, besides other lightweight materials such as paraffin and colophony. Theresults of simulation and test show that using paraffin, colophony or the newcomposite material to fill the suitable place of rectangular steel tubes can increasethe stiffness of the bus body structure. But the filling effect of paraffin, colophonydecrease at high temperature, and the stabilization of new composite material isbetter than others. The simulation of new composite material results also show thatthe improved bus body structure does not penetrate into occupant living space duringrollover crash, and the regular requirements can be met.2. Structure optimization of bus body. The volume of fill ing material and thethickness of steel tube can affect the weight of vehicle, the structure of bus body wasoptimized for lightweight in this paper based on the tube filling method. The uniformdesign method was used to set the experimental scheme on the side pillars and roofcrossbeams of bus body with different thicknesses of steel tube and lengths offillings in the tube. Meanwhile, a series of simulation studies on the bus rollovercrashworthiness were conducted. Based on the regression analysis of the simulationresults, the regression functions were established by SAS software and the designvariables were optimized by MATLAB software. The results show that, under thecondition of meeting the requirement of ECE R66for living space, the total weightof optimized side pillar and roof crossbeam structures was decreased by23.7%.3. Study on the occupant injury during bus rollover crash. The occupant injurycan be aggravated by the complex collision between occupant and occupant as wellas the contact between occupant and internal structures of bus during a rollover crash.Madymo was used to develop and simulate the bus rollover model. According to thecomparison between the MADYMO simulation result and the finite elementsimulation results, this MADYMO model can present the same deformation of bodystructure and collision acceleration as those in FE simulation. There, it can replacethe finite element method to analyze the rollover process. The Euro SID-I dummywas positioned at the impact side seat with the restraints of2-point belt,3-point seatbelt,4-point seat belt respectively to study the injury of occupant. Another EuroSID-I dummy was also added to study the influence of occupants interaction on theoccupant injury during bus rollover. The simulation results show that, although the deformation of bus body structures met the ECE R66, but some part of occupant canstill be injured. Besides that, the interaction of occupants during the rollover processcan cause more serious occupant injury.4. Study on the occupant injury based on the intrusive level of deformed upperstructure into the occupant survival space. Based on the original structure of busbody, five levels of the stiffness of bus body upper structure were increased whichmake the distance between deformed upper structure and occupant survival spaceincreased. Another five levels of stiffness of bus body structure were decreased toincrease the intrusion of upper structure into the occupant survival space. Moreover,one and two Euro SID-I dummy wearing2-point belt were simulated respectively toinvestigate the influence of different levels of the stiffness of upper structure on theoccupant injury. The results show that, whatever the deformation of upper structureis, the contact between occupant and side bus internal structure cannot be avoided.The increase of the stiffness of bus body upper structure can cause more seriousoccupant injury, but the decrease of the stiffness of bus body upper structure can alsocause severe compression to occupant. The best performance of occupant protectioncan be obtained when the deformation of bus body upper structure intrudes thesurvival space with a range that is between-20mm and+20mm displacement relativeto the location that the intrusion just reaches the survival space required in theregulation.5. Study on occupant injury under the condition that the side window is broken.Considering that the side window is usually broken during a rollover crash, o ne ortwo Euro SID-I dummy wearing2-point belt were simulated to study their injuryresponses. The simulation results show that the head and neck injuries can beaggravated under the condition that the side window is opened or broken. Therefore,the best protection performance for occupant can be obtained when the bus windowglass is unbroken.