Study On Fatigue Damage Of Yaw Bearing In MW Level Winde Turbine

Nowadays, wind turbine generator system is booming in our native country. However, the lag in technology induces many key equipments in wind turbine has to be imported. Yaw bearing, one of the key equipments in wind turbine, is a kind of large four point contact slewing bearing, and the load subjecting on it is a combination of axial load, radial load and turnover moment. Owing to its properties of large scale, low rotation speed and complex loading situation the analysis procedure for standard bearing cannot be used. So, it is significant to generate the specific analysis method for this kind of bearings. In order to master the key technology and achieve the localization of wind turbine, the damage failure problem of yaw bearing is analyzed in this paper.(1) In order to calculate the outer loads subjecting on yaw bearing, the coordinate transformation method is introduced to transform the loads acting on wind turbine to yaw bearing. By using this method, the outer loads acting on yaw bearing can be expressed as a function of the motion parameters of wind turbine, and can make the calculation procedure more programmable.(2) In order to calculate the contact loads distribution in yaw bearing subjected by certain outer loads, the coordinate transformation method is used to relate the relative movements of outer and inner ring before and after acted by outer loads using transformation matrix. By this way, the unknowns of the equilibrium equation of yaw bearing are the relative movement parameters. Thus, the contact loads is determined by solving this equilibrium equation. The result turn out that the turnover moment has a grand effect on contact load distribution and it coincides with sine curve. After the contact loads have been determined, the contact ellipse and contact stress is calculated by linear elastic contact mechanics, and these results can provide the theory basis for the design, type selection and fatigue damage analysis of yaw bearing.(3) In the fatigue damage analysis procedure of contact zone, the continuum damage mechanics is used and the material constitutive model which links the damage, isotropic hardening and kinematic hardening is adopted to investigate the influence of plastic flow to material damage. The constitutive model is programmed in user material subroutine UMAT of nonlinear FEM software ABAQUS. The simulation result is studied combined with linear elastic contact mechanics from stress and plastic strain aspects respectively. From the stress point of view, the shear stress under contact surface is the key factor induces the initiation and evolution of damage below contact surface and this agree well with the elastic contact mechanics. Moreover, the Mises stress can reflect the influence of each stress component to the damage comprehensively. From the plastic strain aspect, each plastic strain component can influence the initiation and evolution of damage significantly. Furthermore, the maximum of damage occurs under some distance below contact surface that agree well with the practice and elastic contact mechanics. The results can provide theory basis for both determination of hardened layer and raceway material surface treatment.