Experimental Research On Damage Identification Of Wind Turbine Blade Based On Piezoelectric Ceramics Sensor

In order to meet the world’s continuously increasing energy needs, especially coal and fossil-fuel reserves, currently, various renewable energy sources are being investigated and developed. Among the various renewable energy sources, wind energy plays a very important role (Arakere,2010). For components of the wind power generator, the wind turbine blades are very important, and they may be destroyed in case of the damage happening, bringing a huge amount of economic loss. At present, the vast majority of the wind turbine blades are made of composite materials in the word, and the crack damage is comparatively common failure mode of wind turbine blades. For this reason, a reliable nondestructive testing (NDT) method is necessarily required for the identification of the crack damages.In the first part, in the dissertation, a composite plate with crack damage which is simplified part of the wind turbine blade is experimentally researched by using Piezoelectric Lead Zirconate Titanate (PZT) patches to determine the damage location and level. The experiment system which includes transmitters, a receiver, transducers and a computer used for the signal processing is set up. Some piezoelectric ceramic patches are pasted on the surface of the composite plate with the artificial crack damage. One PZT patch is applied as an actuator, and the others as sensors. An experiment for the crack damage detection was performed by using sine sweep wave generated by actuating PZT patch. Based on the Fourier spectra analysis on the received signals, the artificially mimicked crack area has been successfully identified and the two defined damage indices based on wavelet packet analysis are used to judge the crack damage level.In the second part, a time reversal acoustics (TRA) has been adapted for guided-wave propagation to improve the detectability of local defects in500W small scale wind turbine blade. The basic experimental process is as follows:firstly, the receiver receives acoustic emission signals sent from sound source, and then the relevant PZT sends the time reversed signals, that is to say the PZT patch sends the first received signal at last and sends the final received signals firstly. The divergent acoustic wave generates the self-focusing of longitudinal and shear waves at the same time. In this dissertation, the artificial cracks are made at the foot end of the wind turbine blade. A specific narrowband input waveform with five peaks excited by PZT patches is selected for the experiment. The damage is successfully detected by the process of the received signal and compare between the original signal and the time reversed one. The experimental results show that the feasibility of the developed method.