Research On The High-Speed EMU Wheel And Axle Fatigue Life Based On Flexible Wheelset

With the higher running speed of the train, the range of excitation frequency that the line gets to the vehicle is more extensive. The dynamic behavior of light-weight structure is increasingly prominent. The thesis adopts the wheelset of high speed electric multiple unit (EMU) bogies as object, studies the relationship among its structural stiffness characteristic, vehicle system dynamic behavior, wheel and axle random fatigue life:analyses the effect which the position and shape of the notch on the wheel web hole edge gives to structural static strength and fatigue life; puts forward the treatment method for the notch of the hole.The analyzing model for the structural dynamics of EMU power bogie wheelset is set up by finite element method, so the vibration mode of wheelset in the 0 to 1000Hz is achieved. The definition of torsional stiffness, bending stiffness and umbrella stiffness are given. The axle is divided into eight segments by ’part of the axle’, the physical properties of material of the’part of the axle’ is changed to set up the wheelset model with different stiffness characteristic, and the characteristic frequency of the mode changes. The flexible multibody dynamic theory is adopted to set up the vehicle system dynamic research model which introduced the stiffness characteristic of wheelset. analyze the dynamic response of vehicle under different calculated working condition, and to research the effect which wheelset stiffness and characteristic frequency of the mode gives to the vehicle system dynamic behavior. The research result shows that, the lateral vibration accelerations of the axlebox and the gear have a great increasing with the wheelset umbrella vibration. With the 1st bending mode, the vehicle operating stability and lateral ride comfort is reduced; the derailment coefficient, the sum of guiding force of the wheel-rail, the vehicle wear power, the lateral and vertical vibration accelerations of the axlebox and gear become larger. The effects on the dynamic behavior become larger with the reduced wheelset stiffness and frequencies of the wheelset mode. The other mode has small effect on the dynamic behavior. The wheelset stiffness has very small effect on the vertical force between wheel and rail, wheel unloading ratio and vertical ride comfort.The relationship between the vertical relative vibration acceleration of the unsprung mass and the vehicle running speed is analysed, and it gives reference for the fatigue strength assessment of the axle. The study shows that the maximum dynamic vertical relative vibration acceleration increases with the increase of the running speed.To predict the random fatigue life of the wheel web and axle, the Spagnoli multiaxial cycle counting method and equivalent stress amplitude calculation method base on critical plane are adopted, and the theory of critical distance is adopted to consider notch effect phenomenon. The effects of wheelset structure stiffness on wheel web and axle fatigue life have been studied. The interference fit of wheel and axle is simulated by constraint equations in the three-dimensional finite element model, so the quasi-static superposition method can be applied to the random fatigue life prediction because of the linearization of the nonlinear analysis problem. The analyzing result shows that, the wheelset stiffness has greater effect on the fatigue life of the wheel web; the life decreases with the decrease of the provided several axle stiffnesses. The axle has a smaller fatigue life when the flexible of the wheelset is considered in the vehicle system dynamic model, and the stiffness of the wheel web has little effect on the life of the axle.In order to study the effect which the notch radius and position on the wheel web hole edge gives to structural static strength and fatigue life, the finite element models of wheel with different notch radius are set up. Based on the exceptional load case which is recommended by the leaflet UIC 510-5, the static strength of the holes is evaluated. Based on the load time history which is got by rigid-flexible coupling vehicle system dynamics analysis, the fatigue life of the holes is predicted. The calculation result shows that, there is a big difference among the different notch positions. The stress level of the notchs can be reduced, and the fatigue life can be increased with the increasing radius and without changing the depth of the notch.