Research On Fatigue Crack Propagation Of Pitch Bearing

The pitch bearing is the core component of the wind turbine.Its working environment is harsh and the load is complicated.Under the action of long-term alternating load and impact load,cracks will grow,which will lead to the failure of the entire pitch bearing.Therefore,the comprehensive application of fracture mechanics and finite element analysis technology to study the location of crack occurrence and crack propagation characteristics of pitch bearings has important reference value for safety assessment,life prediction and life improvement of pitch bearings.The main research contents and conclusions of the thesis are as follows:(1)The nonlinear contact finite element model of blade root-pitch bearing-hub-bolt is established,the contact between the ball and raceway in the bearing is simulated by Link10 unit,and the bolt connection is simulated by the rod-beam element method.This model can be used to calculate the extreme conditions The load and stress distribution of the pitch bearing obtains the potential crack occurrence positions of the bolt hole and raceway,and provides boundary conditions for the crack analysis of the pitch bearing.(2)Establish a bolt hole sub-model,insert initial cracks in different azimuths at the maximum stress of the bolt hole,calculate the stress intensity factor of the crack,and find that the 0° azimuth crack is the easiest to crack;on this basis,the insertion depth at 0°azimuth is constant,long and deep The initial cracks with different ratio a/b are combined with the maximum normal stress theory and the Paris fatigue growth model to simulate the fatigue growth of the cracks.It is found that with the increase of a/b,the tendency of cracks to grow in the depth direction gradually increases,but as the cracks grow,The rate of crack propagation along the length direction increases,and the rate of propagation along the depth direction decreases,and with the increase of a/b,the fatigue growth life of the crack gradually decreases.(3)Establish the ball and raceway contact sub-model,calculate the stress intensity factor of the crack at different distances y from the contact point,and combine the Hertz contact theory and the subsurface stress of the raceway to give a mechanical explanation for the change in the stress intensity factor,and carry out the crack propagation mode In addition,it was found that the smaller the angle between the crack and the surface of the raceway,the easier it is for the crack to grow.(4)Establish a single-tooth sub-model,calculate the maximum root stress position according to the actual load,and insert different sizes of initial cracks here.In the case of a certain depth,the study found that with the increase of the aspect ratio a/b,the crack fatigue Propagation life decreases;with the increase of load non-uniformity,the deviation of crack propagation path increases,and the fatigue life of cracks located in the direction of large load decreases,and the fatigue life of cracks located in the direction of small load increases.