Research On The NDT Technology For Wind Turbine Blade Delamination

This paper mainly researches on non-destructive testing for wind turbine blade delamination. It is an effective way to extend the wind power equipment’s life and reduce its maintenance costs. The wind turbine blades are mostly made of composite materials. In other words, this paper mainly researches on NDT for composite materials.This paper firstly introduced several types of delamination in various stages of blades’ life cycle and summarized NDT methods for detecting composite material at home and abroad. When tapping the blade which is delaminated, the stiffness of defects will be decreased and the duration of tap stress will be increased,as well as the sound will be muffled.In the paper, the autor designed a NDT system for the special component. The force and sound signal can be collected at the same time. The author analysed the connection between the duration of tap and the delamination. The spectral of sound which influenced by delamination was also analysed.During the preprocessing part for sound signal, the endpoint of sound was detected based on short-time energy after the trends eliminated by polynomial squares and the nosie reduced by the advanced spectral subtraction method. The features of composite materials delamination were abstracted by spectral analysis and wavelet packet decomposition. The frequency center, frequency variance and mean square frequency during the spectral analysis, as well as the other three parameters which abstracted during the wavelet packet decomposition, can be taken as the features which were used to estimate the composite materials delamination.Finally, the method of delamination test for composite material with BP neural network was studied. The the average accuracy of identification based on spectrum analysis and wavelet packet decomposition reached 93.35% and 88.62%. The the average accuracy of identification based on all the seven features reached 94.72% and 91.58%. According to the methods above, not only can be distinguished whether composite material delaminates or not, but also can be identified delaminated depth effectively.