Study On Ultrasonic Detection Mechanism Of Surface Defects And Analysis Of Characteristic Signal

The engine processing process and working environment often cause defects in its structure,and timely and accurate detection of defects can avoid various accidents.In order to study the defect characteristics of aeroengines,this paper establishes an ultrasonic detection model for metal surface defects by k-Wave numerical simulation.The main research contents are as follows:(1)The effects of ultrasonic source type and edge effect on ultrasonic defect detection characteristics were analyzed.Ultrasonic detection model of key parts of defects was established.The propagation path of ultrasonic waves in defect structure was studied.(2)The ultrasonic detection model of surface defect depth and width is established.The variation characteristics of reflected wave and transmitted wave characteristic parameters are analyzed.The effects of defect depth and width on reflected wave and transmitted wave are summarized.(3)Based on wavelet analysis,the ultrasonic echo simulation signal is denoised;the effects of wavelet basis function,decomposition layer,threshold and threshold function on the ultrasonic echo signal denoising effect are studied;based on signal-to-noise ratio and waveform characteristics Perform parameter optimization.The results show that the number of decomposition layers is 4;the wavelet basis function selects sym8;when the threshold and threshold function respectively select the "minimaxi" threshold and soft threshold,the noise reduction effect is the best.(4)Denoising the measured ultrasonic echo signals of the laser;analyzing the signals before and after the noise reduction according to the energy attenuation theory.The results show that the energy attenuation theory has certain application value for extracting the defect depth value of ultrasonic echo signals;the defect depth error corresponding to the signal before and after noise reduction is reduced;the wavelet parameter selection is used for the noise reduction effect of the simulated ultrasonic echo signal and the measured ultrasonic wave.The echo signal results are consistent.In summary,the research results of surface defect ultrasonic detection mechanism and characteristic signal analysis provide theoretical basis for surface defect detection,numerical simulation,ultrasonic echo signal processing and feature extraction.