Research On Key Technology Of Vibration Measurement Based On Laser Ultrasonic Detection

Laser vibration measurement is a kind of non-contact dynamic measurement method with high detection sensitivity and high precision.It is widely used in the aspects of nondestructive testing,vibration mode measurement and hydrophone calibration.In recent years,with the development of the application field of laser vibration measuring technology,higher precision and sensitivity of the laser vibration measurement are required.Aiming at the problems of vibration signal de-noising and surface wave detection in laser vibration measurement technology,this paper mainly studies the denoising method of vibration signal based on two-wave mixing interferometer and the application of laser ultrasonic vibration measurement system in nondestructive testing,the main work is as follows:(1)This paper presents a wavelet neural network de-noising method for vibration signal based on two-wave mixing interferometer.Firstly,the structure of wavelet neural network is determined by selecting the appropriate number of hidden layers and the wavelet neural network denoising model is established by off-line training.Then regard the out-of-plane displacement and in-plane displacement of vibration signals measured by two-wave mixing interferometer as the input signal of wavelet neural network model.Finally,the denoised signals of out-of-plane displacement and in-plane displacement are obtained by wavelet neural network denoising model.In the experiment,the demodulation method of the two-wave mixing interferometer was verified by simulation,and the denoising effect of the wavelet and wavelet neural network on the vibration signal was compared.Then,the effect of wavelet denoising and wavelet neural network denoising are compared in actual vibration signal measurement.In a word,the effectiveness of the wavelet neural network algorithm is verified by the simulation and the real experimental results.(2)A laser ultrasonic vibration measurement system based on two-wave mixing interferometer is built and the software of vibration signal measurement based on LABVIEW is developed.Moreover,the laser ultrasonic nondestructive testing of P-wave and surface-wave is carried out on testing blocks with artificial defects by this system.In the internal defect detection based on laser ultrasonic vibration measurement,the measurement results are compared with the results of ultrasonic c-scan,which shows the high precision and high resolution of laser ultrasonic nondestructive testing;In the surface defect detection based on laser ultrasonic vibration measurement,the surface defect is located by surface echo and transmission wave,and then the localization result is compared with the actual result.At the same time,the laser scanning method is used to image the surface defects,and the depth of different defects is judged according to the image.The experimental results verify the feasibility and effectiveness of the laser ultrasonic vibration measurement system based on two-wave mixing interferometer.