Analysis On The Expansion Of The Micro-crack Of High Strength Bolt In MW Wind Turbine And Its Fatigue Strength Research

Wind energy as an inexhaustible green energy is the develop-ment trend of the future. But because of the high strength bolt connection failure caused by a tower pour accident,caused the attention of the scientific research workers,and put forward to improve reliability,high strength bolt connection to ensure that the wind turbine operation research problems.In order to study the mechanism of high strength bolt connection failure, the high strength bolts of a MW wind turbine as an example, to study the influence of micro crack on stress of bolt and different preload of bolt fatigue strength.First, high strength bolt connection in MW wind turbines is established3d model and finite element model,based on different preload under the condition of containing micro cracks is obtained by the simulation analysis of megawatt wind turbine of high strength bolt stress distribution and the force of the connection,and combined with relevant theory, design criteria, such as the current situation of research on the reference of high strength bolt preload values range. Second,high strength bolt crack propagation model is established, according to the different crack depth on the high strength bolt thread bottom surface crack and the top surface crack expansion for simulation analysis.Results show that the high strength bolt maximum stress location has nothing to do with the crack position,both appear in the thread connection to the first place. In the initial crack is set in the first thread,because of the high strength bolt connection structure crackle produce stress concentration and crack expansion phenomenon, lead to high strength bolt stress,seriously affect the connection reliability.The last,combined with the actual working status of high strength bolts in MW turbines under different pre-tightening force, fatigue strength of high strength bolt simulation analysis,reveals the high strength bolt pre-tightening force and the relationship between the fatigue life,for the rational design of high strength bolt pre-tightening force provides a good theoretical basis,and use the experiment to test the load of high strength bolt of MW,and find the assembly process results a big dispersion of the preload on the bolt.The actual preload on the bolt could not meet the design requirements, so as to reduce the fatigue life of the bolt,influence the safety of the turbine.47pictures,13tables,63references.