Stiffness Degradation Modelling Of Composite Wind Turbine Blade Based On Fatigue Test Data

With the rapid development of the wind power industry,large-scale wind turbines have become an inevitable development trend.As the most significant part of the wind turbine,blade breaks down frequently due to the complex and varied working load,which has a serious threat to the safety of wind turbine.Therefore,investigating the general rule of stiffness degradation of the composite blade under fatigue load can provide a theoretical basis for the research on fatigue performance and life prediction of wind turbine blade.Based on the fatigue test data of wind turbine blades,this thesis analyzes the stiffness degradation process of wind turbine blade from the fatigue damage mechanism of the composite materials,and explores stiffness degradation modeling method for the composite wind turbine blade under fatigue load.The main research work is as follows:(1)Based on the cumulative damage model of blade composites,a stiffness degradation model of blade composites under fatigue load is established.The proposed cumulative damage model and stiffness degradation model are verified by the test data of various composite materials.The results show that the proposed model has the higher fitting accuracy.The cumulative damage model can properly describe the generation of fatigue damage,the smooth expansion of the composite and the whole damage evolution process in the final stage.The stiffness degradation model can accurately describe the stiffness degradatio n law of different glass fiber composites under different loads.(2)Analyze the stiffness degradation of blade.The fatigue test data of the blade is analyzed by the stress-strain model to explore the stiffness degradation rule.The analysis results show that after the equal number fatigue vibrations with the blade of 20 year life has not reached the failure standard of the blade.Then the main factors influencing the stiffness degradation of the blades are described by combining with the microscopic damage mechanism of composite materials.(3)Verify the model based on the stiffness degradation data of blade.The stiffness degradation model based on the material level in the thesis is fitted and verified by the stiffness degradation data of blade.The verification results show that the stiffness degradation model proposed in this thesis can well describe the stiffness degradation rule of composite blades,and can provide accurate reference and basis for the fatigue life prediction of blades.