Crack Research On Tie Plate Of The Exciter Seat Frame In The DF11G Type Locomotive

Fatigue cracks are the main failure form of the railway products. In this thesis, in order to solve the tie plate crack problem that happened in the exciter seat frame of the DF11G type locomotive, the thesis summarized the study status on fatigue crack failure of the locomotive steel structure and on fatigue failure of steel material in the domestic and abroad firstly. The thesis also compared the methods of predicting parts fatigue life with its limitation. As a conclusion, we advanced the method to solve the crack problem. That is, on the basis of dynamics, though improving the exciter seat frame dynamic performance, to reduce the stress amplitude and times of vibration cycles acted at the fatigue crack point, to obtain the longer usable time. Finally, to achieve successfully the final aim of eliminating the crack and prolonging the usable life time.Through analysis of stress concentration of the tie plate of original exciter seat frame structure, found that the structure produce severe stress concentration because it has right angle shape which was result of simplicity emphasizing reducing the manufacture difficulty. It was one main reason for the problems.The study of welding itself and weld process showed that the welding lines contained shape defects and caused residual stress in the tie plate because of the illogicality of the original design and the process. That is another subordinate reason to cause crack.By using the finite element calculating and test methods, showed the five natural vibration frequencies of the exciter seat frame were in the frequency range when the diesel engine was in common use. This was another main reason to cause the exciter vibration severely, and consequently cause high amplitude of dynamic stress, more times of stress cycle and destine to fatigue crack. It was another main reason for the cracks.Finally, in order to improve the dynamical performance of exciter seat frame, the thesis redesigned the structure of the seat frame and welding process. Through calculating, it found that the dynamic performance of the seat frame was improved greatly. The stress amplitude and times of vibration will be reduced greatly.The new structure is proved to be effect to reduce the vibration of exciter and put to an end to the crack happening by more than one year testing.