Fatigue Properties And Failure Analysis Of Connection Bolt In Wind Power Application

In recent years, the non renewable energy is continuously consumed, so that all countries try their best to develop wind energy technology. Our country is rich in wind energy resources, so the development and utilization of wind energy resources and the development of wind power industry have become an inevitable trend to solve the increasingly serious energy crisis. However, with the installation of a large number of wind power units, a series of safety failure problems are also exposed. The connection of each part of the wind turbine is made of high strength bolt, the connection quality of the bolt can be affected by bolt quality and installation method, ultimately the safety and reliability of the whole wind turbine can be affected. The wind power system is usually working under the action of alternating loads, the high strength bolt is always in the state of fatigue stress. So the evaluation of the fatigue performance of the dynamic load bolt is essential. However, the fatigue failure of the bolts is very difficult to find in preliminary stage. Therefore, in order to prevent the failure of the wind power system, it is important to study the fatigue failure of high strength bolts.Based on the above research background and the above application background, this paper uses the axial pull-fatigue way which similar to actual working condition and through the comparison of two kinds of bolt is used and not used method to determine the hub connected to the blade bolt fatigue performance. Considering the factors such as: actual service connection bolt load, the maximum load rating of fatigue testing machine and the cross-sectional area of the connecting bolts, etc. We prepared the hollow fatigue test bar to expanding the scope of the stress test, so the average stress in the selected cover the actual service condition. In this paper, the failure of the variable pitch bearing and the connecting bolt of the hub and the connecting bolt of the tower are analyzed. The main reasons for the failure of the connecting bolts are analyzed, and the preventive measures are put forward.The paper’s main conclusions are as follows:1、when mean stress was certain, the fatigue life of the coupon reduced as stress half range increased. In the same test conditions, the fatigue life of the used bolt was only 30%～60% compared with the unused bolt’s.2、The shear stress of the bolt caused by disassembly was about 40% of the axial stress. The actual maximum principal stress was closed to its breaking strength.3、There is horizontal fatigue fracture in connecting bolt threaded parts of pitch bearing and hub.cold rolling process streamline dose not appear on the tooth portion surface of failure bolt,and there is an obvious decarburization on the surface,which greatly reduces the fatigue resistance of the bolt tooth portion,fatigue fracture occurs from outside under alternating loads.4、Decarburization and creep caused the loss of prestressing force, coupled with the bolts by the effect of radial force service, finally caused the tower drum bolt looseness.