| A domestic special semi-trailer is widely used in long-distance transportation of Military heavy tracked equipment. Driving road conditions not only include highway and urban arteries, also include some poor road conditions. Road conditions are complicated. The frame fracture phenomenon often appeared in the junction between the gooseneck and traction plate, the connection between the suspension bracket and the lower wing in the process of actual use, and then leads to structural damage, thereby affect the completion of march task. Because of the particularity of the transported equipment, the special semi-trailer is different from the general semi-trailer on the structural characteristics and mechanical characteristics. It needs higher strength requirements in spar, and the load distribution is uneven. On the other hand, there is not enough theoretical analysis and experimental study for the special semi-trailer structure. The improvement and modification of the general semi-trailer model cannot be directly applied. Therefore, it is necessary for the fatigue life analysis to find out the reason leading to fatigue fracture, and put forward some suggestions for improvement. This paper has important significance for the design and manufacture of the special semi-trailer. The main works of this paper are:(1) According to the fatigue fracture phenomena appeared in the process of actual use, a finite element model for some special semi-trailer frame is established, on which a static analysis is conducted with its stress distribution and deformation obtained in main conditions.(2) The normal mode analysis was performed for the semi-trailer frame. The main natural frequency resonance and vibration type were obtained. Based on the multi-body dynamics theory, a rigid-flexible coupling multi-body dynamic model is set up. Then run the full vehicle analyses with load spectra and the PSD of acceleration of the trailer body centroid under4grade roads acquired. Then the dynamic characteristics of the frame were evaluated in order to find out its weaknesses. Based on these, some modifications were suggested on the semi-trailer frame. It offered a feasible method in the research of the design optimization for the semi-trailer structures.(3) With the consideration of the load spectra sequences influence, two load spectra of mixed road spectra are acquired. Then compared the analysis results of the two load spectra by calculating the fatigue life. It is proved that the1st load spectra analysis procedure yields comparatively conservative results. Based on these, by considering of the surface state, the fatigue life is estimated. Analysis results show that:Compared with traditional method, the method can help to give a more reasonable result. Some locations in the frame with shorter fatigue life are modified and get good results.(4)Based on the analyses result, an optimization is given to the frame in structure, manufacturing process and the selection of the raw material three aspects. Then re-analyze the characteristics of the optimized frame.Analysis results show that:The frame meet the operating requirements.This paper uses the multi-body dynamics, finite element analysis and fatigue analysis, to predict the fatigue life of the semi-trailer frame. Compared with actual failures, the result proves the accuracy of the model. An optimization about the structure and manufacturing process of the frame is provided. Some requirements about the selection of the raw material are put forward and achieved good effect. This paper is instrumental for optimization design of the special semi-trailer frame. |
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