Research On Acoustic Emission Detection And Identification Of Main Beam Damage Of Wind Turbine Blade

Wind turbine blade is the core bearing component of wind turbine,its quality and safety will affect the stable operation of the whole wind turbine,once the damage and fracture will cause serious safety accident.The main beam is the main load-bearing structure of the wind turbine blade,but due to the particularity of manufacturing technology,delamination,folds,voids and other defects are easy to appear in the processing of main girder composites.Among them,delamination defects cause local stress concentration and reduce local strength in harsh service environment,which is the main defect type that induces blade damage.This thesis takes the artificially prefabricated layered defect wind turbine blade main beam composite material as the research object,and clarifies the damage evolution stage changes of the main beam composite material to achieve the purpose of damage identification.The main research contents are as follows:By analyzing the fatigue damage mechanical characteristics of the blade composite material,the force form of the main beam composite material and the main damage mode of the main beam composite material are determined.Since the main beam is laid by unidirectional fiber cloth,the loads related to fiber damage are the axial load perpendicular to the fiber surface and the longitudinal load parallel to the fiber surface.Loads applied in other directions have little effect on the stiffness of the fiber.This paper analyzes the damage evolution of the main girder with the loads perpendicular and parallel to the fiber direction as the main load,and thus determines that the loading test methods are tensile test and fatigue test.According to the structural characteristics and manufacturing process of the main beam of large-scale wind power blades,the composite material laminated plate specimens of the main beam with delamination defects were prepared to carry out tensile test research.Based on the kernel improved fuzzy cluster analysis(KFCM),the damage mode of the main beam composite material was identified,and the characteristic frequency range corresponding to the four damage modes of matrix cracking,fiber peeling,interface delamination,and fiber fracture were determined.Analyze the amplitude,energy,impact count and other parameters of the acoustic emission signal,and found that the change of signal characteristic parameters can well reflect the damage change of the main beam composite material.By analyzing the acoustic emission characteristics of the main beam composite with delamination defects,the effect of layered defects of different sizes and different depths on the mechanical properties of the main beam composite is determined,and the basis for the damage identification of the main beam composite is provided.Based on wavelet analysis and fast Fourier transform signal processing methods,the acoustic emission signals of the three stages before,during and after fatigue loading experiment are collected respectively.The acoustic emission signals with typical characteristics of the main beam composite specimens with no defects and with delamination defects were extracted for comparative analysis at each loading stage,and it was verified that the characteristic frequency of damage at each stage changes with the damage mode.The characteristic parameters of the transmitted signal can identify different damage modes and provide a feasible reference for the health monitoring of wind turbine blades.