| With the increase of the running speed, more and more problems about fatigue strength of carbody structure appear in the running process. Carbody fatigue strength evaluation criteria still remain in the stage of 200 km/h in our country. Therefore, there is a lack of systematic research on carbody service condition of EMU over 300 km/h. Neither carbody vibrations under different service environment nor the influences of the aerodynamic load have been considered in these evaluation criteria. The demand of carbody fatigue strength in European standard UIC566\EN 12663 is quite different from the current running mileage, using density and maintenance system of EMU existing in our country. A systematic study of EMU train service load and an experimental research on the carbody fatigue test are of great significance to the development of EMU carbody in our country. In this thesis, we mainly carry out the following work.(1) With a comparison of common fatigue strength evaluation criteria at home and abroad, a basic method to evaluate the fatigue strength of aluminum alloy car-body structure has been proposed based on DVS1608 standard. Considering the influence of cyclic loading on the material and the allowable fatigue strength of the weld joints, multi-axial stress evaluation method has been occupied in the calculation process of exploitation degree of the parent metal and weld joints in this thesis, and the total exploitation degree of the evaluation points has been modified.(2) A systematic study on the fatigue load spectrum of the carbody has been conducted. According to the time history of carbody loads obtained from field tests and dynamic simulation, it has been dealt with zero drift, abnormal wave, filters and invalid amplitude. Then the load spectrum could be extrapolated to 106. On account of its mean and amplitude distribution function, the extreme value of the load spectrum could be determined. The normal load spectrum, which could be made from the extreme value, has been applied into fatigue tests eventually.(3) The rigid-flexible coupling dynamic model of high speed EMU has been established to simulate wheel tread wear, failure of anti-hunting damper, loss of air pressure in the air spring and the time series of carbody acceleration on the straight line, on the curve line and through the track switch, and to evaluate the influence of different working conditions on carbody damage. The time series of stress and displacement of the carbody under the aerodynamic load can be yielded to evaluate the damage of the key points on the carbody by combining aerodynamics and vehicle system dynamics simulation.(4) Based on a systematic research of carbody fatigue test at home and abroad, a basic scheme of the inertia loading test bench has been proposed. Through the analysis of influences of expansive pneumatic load and compressed pneumatic load on carbody strength, a plan of the test bench construction considering the aerodynamic load and inertia load simultaneously has put forward, and the test bench has provided help for the construction of test bench for the EUM whole body fatigue evaluation.(5) The EMU whole body fatigue test methods including the constant amplitude loading test, the varying amplitude loading test, the stochastic loading test and aerodynamics loading test have been researched. The dynamic stress of key points on the carbody has been tested to evaluate the carbody fatigue lifetime. And the recommended draft of carbody fatigue test has been proposed.(6) Fatigue test research on the local prototype of carbody has been carried out. Based on principles of deflection and stress level consistency, the equivalent treatment method and constrained boundary method of local prototype load have been put forward. Then these methods have been verified on the test bench, and they will provide a more reasonable plan for EMU carbodv fatigue strength test. |
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