Research On The Dynamic Behavior Of Flexible Frame On High-Speed EMU Bogie

With the higher running speed of the train, the range of excitation frequency that the line gets to the vehicle is more extensive. While running, the dynamic behavior of light-weight structure is increasingly prominent. The thesis adopts the welded frame of high speed electric multiple unit (EMU) bogies as object, studies the relationship among its structural stiffness characteristic, vehicle system dynamic behavior and frame fatigue strength, and puts forward the designing method for the structural strength and stiffness of torsionally flexible bogie frame.The analyzing model for the structural dynamics of EMU trailer bogie welded frame is set up by finite element method, so the vibration mode of frame in the low frequency range is achieved. The flexible multibody dynamic theory is adopted to set up the vehicle system dynamic research model which introduced the stiffness characteristic of bogie frame, and analyze the dynamic response of vehicle under different calculated working condition. The study shows that the bogie distorting vibration has no effect on the stability and ride comfort of the train running. After adopting the frame distorting vibration mode, the distortion stiffness of bogie system is lower than rigid model; while the vehicle is on the warping line, the vertical load of the wheel is approaching to well-distributed, and its wheel unloading ratio and maximum vertical force between wheel and rail have dropped. While analyzing by using quasi-dynamic method, the derailment coefficient has dropped. The vibration power of frame bending and shear mode is low, and the vehicle system dynamic behavior would not be changed.To simplify the distortion stiffness experiment and calculating method of bogie system, the ratio of twist load to frame vertical deflection is defined as structural distortion stiffness. The physical properties of material is changed to set up the frame model for the different distortion stiffness characteristic, and to research the effect which distortion stiffness gives to the vehicle system dynamic behavior. The analyzing result shows that, the lowering frame distortion stiffness would let the vertical interaction between vehicle and rail re-allocate, the vertical load of the wheel is approaching to well-distributed. So the maximum vertical force between wheel and rail and the wheel unloading ratio low with the lowering frame distortion stiffness while passing through curve. The low frame distortion stiffness has very little effect on the running stability, ride comfort, derailment coefficient, and the sum of guiding force per axle. Starting from the running safety of vehicle on the warping line, the low figure would be chosen for the frame distortion stiffness.In order to overcome the defect of present method, the method based on the degree of utilization is recommended by FKM to evaluate the frame fatigue strength. Considering the manufacturing technology and service condition of high speed EMU welded frame, the effect which the average stress and load spectrum characteristic have given to the frame fatigue strength is illustrated. According to the stress calculating method under element coordinate, the analyzing stress spectrum of the weld toe which connect the web and the bottom cover plate of the side sill are fixed. The degree of utilization is calculated, and is compared with the evaluation result based on the traditional method. In the convention of traditional method, the vehicle passing through curve as a quasi-static process is the determined element for the structural fatigue strength, the effect which the dynamic vertical process made by the bounce movement is quite low. The effect of load cycle in the quasi-static and dynamic loads is considered by FKM method. When the fatigue resistance on the joint gets agreement, the evaluation result for the structural fatigue strength based on this method is looser than the traditional method. Evaluating the structural fatigue strength by FKM method is beneficial for the light-weight structure design.In order to study the effect which stiffness characteristic gives to structural fatigue strength, the frame model for variable distortion stiffness is set up. Based on the experimental load spectrum which is recommended by the leaflet UIC515-4, the frame fatigue strength is evaluated. The research result shows that, to low the frame distortion stiffness would make more deflection in twist load sensitive area. In the high stress condition, the normal stress degree of utilization, the shear stress degree of utilization and the overall degree of utilization in this area have all increased. The low stress joint in twist load sensitive area is the basic principle for the torsionally flexible bogie frame strength design.The bending and distortion stiffness characteristic of the beam with different section is analyzed. The result shows that, when the wall thickness and the area surround by neutral plane of tube transom and the wall thickness of box transom is equal in quantity, compared with tube transom, the box transom has low distortion stiffness, but its bending stiffness is high. The calculation result based on the finite element method shows that, the frame distortion stiffness has been influenced by both the bending stiffness and distortion stiffness on transom. In different wall thickness condition, the difference exists in the effect that bending stiffness and distortion stiffness on transom give to the distortion stiffness of the frame. The design for torsionally flexible frame should take in coordinating different stiffness characteristic of the transom structure as the basis, and low the distortion stiffness for the frame structure by improving the flexible standard in the transom.