Research On Durability Analysis Method Of Integrated Coach Body

Durability of the coach body structure is an important performance to be considered , and that the acquisition of dynamic stress is the key problem.Predicting the potential durability issues during upfront engineering using finite element method is a good way to drastically reduce new product development cycle and the number of testing prototypes,then the efficiency and the success rates of product design will be improved.There are still some problems in the popular procedure for evaluation of coach body structural durability.Three main problems were discussed in this paper:(1) simulation of the nonlinear character for the suspension system and the tire-road system is difficult;(2)no uniform coach body FEM model is available in early stage of product design;(3)dynamic durability analysis always results in a large amount of result data and a long term of analysis cycle.According to these problems and the specialty of de integrated coach body,several particular technologies were presented in this paper.By this way,the dynamic durability analysis method could be easily introduced into the preliminary design phases of a coach.Primary research contents of this paper are as followed.In the first chapter,development of coach body structure design in our country and character of integrated coach body structure were expatiated.Development of fast auto body structure durability analysis methods was analysis.The Advantages and disadvantages of these methods were discussed,then a result was gotten that a more effective fast durability prediction method for the coach body structure was needed to be studied.In the second chapter,three main problems of the popular durability analysis procedure were described in detail,and the causations of them were analysis,then corresponding measures were presented to deal with theses problems.Vertical dynamic displacements at the mounting points of the coach body frame were used to be the dynamic loading input for the transient analysis,in order to solve the problem of the vehicle's nonlinear behavior.Then the nonlinear suspension and tire-road system were not needed to be considered any more,and the integrated coach body structure model was simplified to be a single liner elastic model.By this way ,the procedure to verify analysis model would be simplified and the simulation difficulty would decrease,while the efficiency of simulation would be improved.In order to extract the stress history of the bar elements from transient analysis's result,a computer code was programmed.Then the fatigue analysis of a coach frame which was set up with bar elements could be carried out on the platform of MSC-Fatigue.With this technique,a common analysis model could be used during the preliminary design phases of a coach structure,and analyzers could easily perform the structure analysis and optimization.As the bar elements model could not describe the detail of stress disputation in the joint area,limitation in simulation was resulted . Joint-superelement model and dynamic reduction technique were employed to settle the problem.Then a conservative fatigue prediction application,by which the complicated multi-axial stress state was simplified into a simple uniaxial stress state,was carried out to gain the fatigue life of the whole body.The combination use of bar-element model and joint superelement model is a good way to greatly reduce the simulation cost and improve analytical precision.In order to verify the reformed durability analysis procedure in this paper,a small partial model of a coach was set up,and a dynamic as well as a durability experiment were performed on it.According to the data measured in the experiment and the computer simulation result of three FEM models, some conclusion was gained:(1) bar-element model,joint-superelement model and detail model set up all with shell elements,all of them showed a high precision in dynamic analysis;(2) as the bar-element model could not describe the detail stress state at the joint area and the dynamic exciton was too small,the critical areas may not be predicted,then the dynamic stress of bar-element should be corrected by multiplying a appropriate coefficient;(3)the bar-element model was the most effective,the shell-element model was the most inefficient,while the joint superelement consumed more time than bar-element model,but still showed more effective than the shell-element model; (4) the simulation precision was contrary to the simulation efficiency,and the result gained from the superelement and the shell-model were almost the same.The conclusion of the partial model indicated that the reformed durability evaluation method of integrated coach body structure was resultful.Based on the reformed durability evaluation procedure,a durability prediction of an integrated coach body structure was performed in chapter four.The choices of some key parameters were discussed in detail.The analysis indicated that the reform procedure was feasibility.Chapter five summarized all through this paper and a result was gotten that the reformed durability analysis procedure has overcame some of limitations of the popular durability analysis procedure,which made it possible to evaluate the durability of an integrated coach body during the upfront engineering stage.Therefore there is a better foreground for the reformed durability analysis procedure.