Research On Wind Turbine Blade Health Monitoring Based On Π Phase Shifted Fiber Bragg Grating Acoustic Emission Sensing Technology

As a non-destructive on-line testing technology,acoustic emission testing technology is widely used in industrial equipment fatigue testing and large-scale structural health and safety testing.The technology evaluates the integrity and performance of the parts to be tested by analyzing the acoustic emission signals of the parts to be tested.Fiber Bragg grating(FBG)sensor has the advantages of high sensitivity,small size,no electromagnetic interference,and easy to be embedded in the parts to be tested.In this paper,based on the investigation of acoustic emission detection technology and optical fiber sensing technology,small fan blades and steel plates are taken as the research objects.Around the acoustic emission detection technology,a series of research work is carried out from the construction of fiber Bragg grating acoustic emission detection system,acoustic emission signal denoising analysis and acoustic emission source positioning technology.(1)The sensitivity of FBG and π-FBG is compared and analyzed by using the method of tunable narrow-band light source demodulation.An acoustic emission detection system based on π-FBG is proposed.The standard signal of acoustic emission is detected by using the system,and the measurement results are compared with those of traditional piezoelectric sensors.It is proved that the system can successfully detect the acoustic emission signal,and the correlation characteristics of π-FBG are analyzed The feasibility of the method is studied,which lays a foundation for the subsequent acoustic emission signal analysis and acoustic emission positioning.(2)In order to eliminate the noise interference in acoustic emission signal and solve the problem of poor denoising effect of wavelet packet denoising at low noise ratio,the wavelet packet threshold denoising method based on empirical mode decomposition(EMD)is studied.By comparing the signal-to-noise ratio(SNR)of simulation signal with different denoising methods,it can be seen that the wavelet packet threshold denoising method based on EMD has good denoising effect at different SNR conditions Noise effect.(3)I In this paper,small fan blades are taken as the research object to simulate two different kinds of common damage: matrix fracture and internal fiber layer fracture.The two kinds of damage signals are de-noising,and the wavelet packet energy feature extraction method is used to extract the features of the two kinds of damage.(4)In order to solve the problem of acoustic emission source location,taking the steel plate as the research object,an acoustic emission location experimental platform was designed and built.The time difference method(TOA)and time difference diagram(delta T)were used to carry out acoustic emission linear location and plane location experiments on the steel plate.