| Welding spots of the cab BIW have a great impact on the dynamic and static performance of commercial vehicles, such as the structural strength and stiffness, the low intrinsic modal frequency and so on. From the production cost, unreasonable spots layout will increase the number of welding spots and the cost of the welding process. From the mechanical point of view, severe stress concentrations emerge near the spots will result in easy fatigue cracks and affect the cab connectivity. From the point of fatigue failure, for the spots welding structure, failures often take place in the welding spots area and cause accidents. Thus, to optimize the layout of welding spots and predict the fatigue life in the early design, have significance for improving the overall performance of the body structure and reducing the cost of welding assembly process.First of all, this paper describes the status of domestic and foreign researches and developments of the spots layout, and the basic theory of topology optimization and fatigue, which including the topology optimization methods and the used mathematical models, the concepts of fatigue damage and fatigue life prediction methods, which provide a theoretical basis for future research.Secondly, the finite element model of the cab BIW of commercial vehicle was created by the finite element method and the static stiffness and strength were calculated. In the modeling process, four common used spot elements which are RBE2, CBAR, CWELD and ACM were used to simulate the welding spots of the cab. And then by coMParing the advantages and disadvantages of the four models, the CWELD element was chose for the welding simulation. After that, the strength and stiffness calculation of the cab were taken, which were prepared for further study.Then, based on the synthetic optimization division method, the optimization of the spots layout of the cab body was taken. First, taking the overall torsion stiffness and the low frequency mode as the maximum goal, five different solder volume as the constraints, then the topology optimization was taken. The optimized distributions of solder joints of the five programs were gotten, as well as the overall torsion stiffness and the low modal frequency of the cab. After analysis, we got the optimal solution and the stress analysis of the cab after optimization was taken. Experience has shown that, severe stress concentrations emerge near the spots, resulting in easy fatigue cracks and affecting the cab connectivity. We can get these conclusions as following before and after optimization, the torsion stiffness and the low Modal frequency were both decreased, which does not meet the requirements of the optimal spots layouts. Then, based on the above deficiencies, this paper applys the partition synthesisâ‘ plimization method for cab. Based on the different influence of the cab structure thickness to the stiffness, strength and frequency of low order modals, the cab was separated into two different areas of A and B using sensitivity analysis. On A area, according stiffness and strength to adjust number and position of spots.B area uses topology optimization methods to optimize the layout of the solder joints. And then, the solder joints layout optimization of the cab was obtained.Finally, based on the fatigue theory, the fatigue life of the spots was analyzed. Multi-body dynamics simulation method was used to get the load spectrum. The model, load spectrum and materials were imported into the fatigue analysis software, and the life of spots of the optimized and the original models were obtained. By coMParison we can see that the life of optimized spots was increased.By using partition synthesis optimization method, the cab was divided into two functional design areas. Different layout optimization methods were used for the characteristics of different regions. The engineering practicality of the optimization results were improved by using this method and the spots layout optimization of other structures can also be guided for.
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