Study On The Key Technology Of Design And Optimization For Coach Rollover Crashworthiness

With the development of national economy and the demand for road passengertransport, coaches and buses have become one of the most important transportation vehicles.Traffic accidents happen frequently with the increase of automobile inventory. Although theprobability of coach rollover is less than the other types of accident, large casualties andfatalities are usually involved in rollover accident. With the aim of enhancing the capabilityof occupant protection for coaches in a rollover accident, the consultative draft of the newGB concerning the rollover safety of coaches and buses has been released and will takeeffect soon. With the severe situation of rollover accidents, the higher standards proposed bythe new regulation, and the inadequate development of research and design methods forrollover safety, there is an urgent need for the study on the design guidelines andoptimization technology for coach rollover safety. In this context, the in-depth study on thekey technologies of coach rollover safety design and optimization has a vital significance,from the perspective of scientific research and engineering application.Limitations of the study on the coach rollover safety are summarized based on thestatistics on the coach accidents during the recent years and the literature review, followedby the contents and technique route of this study. The procedures of the finite elementanalysis (FEA) of coach rollover are summarized which finds the pre-processing is a highlycomplex and intricate task. Therefore, a software framework that covers the technicalprescriptions of ECE R66is proposed and an automated pre-processing tool for coachrollover simulation is developed. A case study shows that the automated tool makes themodelling process standardized and more efficient. The automated tool provides thepre-processing tool for the subsequent rollover simulation.A full scale coach body section is fabricated in accordance with ECE R66and a tiltingplatform is designed and created. The experimental scheme that is capable of capturing thedynamic histories of structural responses is designed and proposed. Coach body section rollover testing considering the dynamic history of structure deformation is performed andthe dynamics responses and local buckling behaviours are observed. The FE model of coachbody section is developed. Coupon tests for material properties are performed to provide thestress-strain data for FE model. Simulation of body section rollover is performed thatobtained the structural dynamic responses. Results show that the residual space is notinfringed during and after the testing process. Deformation mechanisms and weak spots areanalyzed of the body section during and after the rollover process. Good agreement betweenthe results from the simulation and experiment are presented in terms of body sectiondiagonal deformation, sidewall pillar intrusion and impact acceleration, which indicates thatthe accuracy of the FE model is validated. The validated FE model provides a modellingmethod for rollover analysis of the complete vehicle. On the basis of the body sectionrollover experiment, a technological process that is easy to implement in product R&D andintegrates the simulation analysis and experimental testing is proposed for the evaluation ofcoach rollover safety.The full scale complete vehicle FE model is developed based on the modelling methodand the automated tool. The influence of superstructure configuration on the rolloverresistance is studied. Structural performance index, including the relative residual spaceintrusion amount, the distribution of energy absorption, the deformation mode and theimpact force and the ratio of kinetic energy and internal energy (K2I) are calculated andinvestigated in detail, upon which the rollover safety performance for each model isevaluated. A novel sidewall structure, named "Extended sidewall" is invented whichimproves the coach rollover safety significantly. Then design guidelines for the coachskeleton design aiming at the rollover safety are proposed.In order to enhance the coach rollover crashworthiness, a multi-objective optimization(MOO) is formulated and solved with the integration of sensitivity analysis, design ofexperiments, surrogate model and multi-objective genetic algorithm. The Pareto front isobtained, from which two solutions are selected and computed using FEA. Results showthat the residual spaces of the two solutions are not infringed, thus the adoption of MOO to optimize coach rollover safety is validated. Lightweight design of coach chassis and floorassemblies is carried out with the integrated application of reduced model and optimizationwith hybrid design variables. Optimization techniques based on three types of variables, i.e.,continuous, discrete and hybrid design variables are utilized and compared, which indicatedthe rounded off results from the first method may not meet the constraints. The optimizedresults from the hybrid optimization method not only satisfy the constraints, but also meetthe gauge specifications. Consequently, it is applicable for lightweight design using thecombination of reduced model and hybrid variable optimization technologies.