The Research Of CAE Modeling Method Of Integrated Coach Body Joint

CAE technology that based on the finite element theory is widely used in the product improvement and the optimized design of the coach. The structure analysis of coach body is an important constituent of its exploitation process and it is an important basis for the coach design. The content of structure analysis of coach includes static stiffness analysis, dynamic model analysis, fatigue analysis, NVH analysis, and impact analysis and so on. All of these results are correct or not directly depended on whether or not the CAE model that we set up correctly reflects the mechanical characteristics of actual structure. Now days CAE analyses of the overall coach model increasingly maturate but there need a further study of the details of the local modeling.The joint of coach framework is an important part of the coach body structure .Generally speaking the crack problems of coach is come from the joint location. The level and concentration of stress is the important attention of forepart invalidation analysis about the body framework of coach. The structure modality and local connection fashion of actual component is the important influence complication of stress concentration.There are two primary methods for set up the finite element model of the body framework of coach in the finite element analysis: beam element or shell element to set up the model. At present the beam element method of modeling is the main method. The advantages of beam modeling method are as following: it is convenience and simple to setup the model, the scope of model is small, the speed of compute is quick, the modification of the model is convenient, and it can give a macrocosm evaluate of the stress level of the whole framework of the coach .But this method don't think of the form ,the connect fashion and local details of the joint .It directly see the joint as the rigid connector and use a node to connect it .So it compute a higher stiffness result than the true stiffness of the coach . And there is not part of the calculation of joint stress concentration, unable to realize the joint local modification. With the development of the computer hardware and software technology the application of shell element modeling is developed. It is possible to set up a detailed model of the coach almost without simplified. But shell element modeling has its disadvantage that can not be ignored such as : the workload of set up the coach model is large and time-consuming ,the finite model scale of the whole coach is big, the consume of the compute is great ,the modification of the model is difficult . So it is not suitable for the initial design process in which the optimization needs to modify the model frequently.When the coach carrying, the joint part of profile bar endure a large force while the middle of the profile bar endure a small force. The stress concentration of joints has important guiding significance to the design of the coach skeleton. The shell element model can figure out the detailed stress of the joint part. But at the initial stages of the design the model needs optimization and modify frequently, use the shell element will extend the exploitive time of the coach. Set up exact joint model based on the beam model will commendably relax the contradiction of the accuracy and economy of model. This paper presents two methods to set up joint model in the CAE analysis of the coach, which are joint equivalent model and joint super element model.Traditional beam element model is based on the center line of the profile bar. But at the joint the center line of the bar didn't connect, so we prolong the center line and connect them. We endow the prolong part the property of the beanpole, use a node connect the joint rigidly. It result that at the joint, the beam element model is different from the reality connection of the profile bar and lead to a big error. The joint equivalent model separate the prolong part from the center line,and call it equivalent short beam ,calculate the property of itself. When it comes to the joint of the coach, first we set up detail T joint shell model in the same size. Calculate the stiffness of the model. Then calculate the stiffness of the equivalent short beam. Further more we can get the parameters as cross-section area A, inertia moment I XI YJ of the equivalent short beam. Add the equivalent short beam to the complete beam model of the coach, so it improved the calculate accuracy of the beam model. Joint equivalent model made amendment to the traditional beam model from the perspective of stiffness.The joint super element model uses the shell element to set up the joint model, while uses the beam element to set up the main part of the coach framework, and then connect the two part properly. In the traditional combination model people use the shell element to model the components that need attention, while use beam element to set up the components that needless attention. In this paper we developed the method of combination model deeply. As to a pillar, use shell element to set up the joint part and use beam element to set up other part. In this way, we can get all of the related parameter that needed in the structure design in one compute process. This paper discussed the method of set up the joint super element model in detail. And validated that use this method can get almost the same calculation accuracy as the full shell model. Experiments shows that use this method to set up modal are feasible and accurate.Finally, in this paper the joint super element model as mentioned in the paper was applied to the coach CAE analysis. We have a deep discussion and study in the connection form of the side-windows pillar and the longeron below the window. The results show that, under the bend loading case the two connection form do not impact the stress of the coach skeleton too much. But under the torsion loading case, when the side-windows pillar transfixion it will greatly reduce the joint stress level.In this paper we studied the method of set up joint modal in the CAE analysis of the coach, and presented the joint equivalent model and joint super element model. The use of joint model improved the calculate precision of coach CAE model obviously, and saved the calculate time .Along with the development of the auto industry, the joint structure will get more and more recognition. The model of the whole vehicle will be continually refined and improved. The calculate speed will be faster and the result will be more precision.