| Frame is the main bearing structure of tractor and fatigue damage is the major damage form under all kinds of dynamic random loads in the process of work. Fatigue life prediction for frame is of great significance to tractor working reliability. Fatigue life research of the tractor frame proceeded by virtual prototyping technology can greatly shorten the development cycle, reduce development costs and improve the design quality.In this paper, KAT1804type tractor produced by Xuzhou KAT Machinery Company was studied. The fatigue life of frame structure was predicted in virtual environment via the multi-body system dynamic simulation, the finite element method and fatigue life analysis.Firstly, a three-dimension solid model was established by PRO/E and was imported to ADAMS by MECH/PRO, the multi-body dynamic model was created combined with road model and tire models, the7random load time courses of the frame in the running course were calculated. The road roughness of grade E standard road was simulated by partial wave adding model, the road file applicable to tractor simulation was written and road model was generated. The tire files were wrote according to tire parameters, the tire models were established in ADAMS combined with tire quality inertia parameters.Secondly, a finite element model of the frame was built by the use of ANSYS. The stress influence coefficient was obtained through quasi-static stress analysis. The results show that the frame structure is reasonable.Thirdly, model analysis was accomplished by the use of both experiment method and simulation method. The low order natural frequencies and vibration modes were obtained, which show that dynamic characteristics of the frame is reasonable. The relative error between tested value and calculated value was analyzed, which shows that the finite element model of the frame established is reliable.Finally, the fatigue life of frame was predicted by the use of MSC.FATIGUE, combined with random load time courses obtained by multi-body dynamic simulation, stress influence coefficient and S-N curve.The results show that, the frame design of this type of full-frame tractors can satisfy the demands of fatigue life. The comparative dangerous areas are located at the bending place of the rear axle mounting plate; other locations almost have an unlimited life. Lightweight frame design can base on this fatigue life model.In conclusion, this paper introduces the method based on MBS-FEM to evaluate frame structure fatigue. This integrated method can be used in early stage in structure design to predict correctly frame structure fatigue property, which can provide a theoretical basis for the optimization design of the frame structure. |
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