Study On Mechanical Properties And Fatigue Life Of Connecting Bolts Of Pitch Bearing

Wind turbine pitch bearing connection bolt group is the key component of wind turbine pitch system,which is responsible for connecting pitch bearing with blade and hub.During the working process,it bears complex load conditions,and its life has a significant impact on the reliability of wind turbines.China has a vast territory and abundant wind power resources.In recent years,the proportion of wind power energy has increased significantly.Wind power has broad prospects and huge market.However,there is still a big gap between China and foreign countries in the field of wind power technology.Many key components depend on imports.Therefore,it is necessary to conduct in-depth research on key components of wind turbines,especially fasteners-connecting bolts.In view of this situation,the main contents of this paper are as follows:Firstly,An integral finite element model of "blade-pitch bearing-pitch bearing connection bolt set-hub" for a MW wind turbine pitch control system is established.The coupling model of "Beam 188 beam element" is adopted for the pitch bearing connection bolt set.A self-designed and self-assembled experimental platform for connecting bolts of pitch bearing of fan is designed and assembled.Under different load conditions,the stress of the experimental bolt group is extracted and analyzed by strain gauge.Then,the whole finite element model is built according to the test bench,and the experimental bolt is simulated by the coupling model of Beam 188 beam element.The feasibility of the model to simulate the connection bolt of pitch bearing is verified by comparing the experimental data with the finite element calculation results.On the basis of the whole finite element model The finite element analysis is carried out under the condition of limit load,and the influence of these factors on the mechanical properties of the connecting bolt group of pitch bearing is explored by changing the parameters such as diameter,pretightening force and length of the connecting bolt by controlling variable method.On the basis of the whole finite element model,the functional relationship between the maximum tensile stress and the load of bolt group under fatigue load is fitted.Then the S-N curve of the connecting bolt of pitch bearing is determined and revised according to GL2012 code.The accumulative fatigue damage and fatigue life of the connecting bolt group under 20 years rated life condition are calculated by using Miner's linear fatigue damage theory and the load-stress function relationship.The results show that the coupling model of Beam 188 beam element is feasible to simulate pitch bearing connection bolts;the influence of factors such as diameter on the static strength of pitch bearing connection bolts is studied;and the calculation method of fatigue life of pitch bearing connection bolts is given.It plays a guiding role in the design of pitch bearing and the selection of bolts in engineering practice.