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Influence of cross correlation step length on stress evaluation of low signal noise ratio ultrasonic waves

LIU Bin;MIAO Wenbing;Provincial Key Lab of Advanced Welding Technology,Jiangsu University of Science and Technology;  
Based on ultrasonic acoustoelastic theory,the influence of cross correlation step length on stress evaluation of low signal noise ratio ultrasonic waves was discussed with theoretical calculation method. Based on damped oscillation cosine signals,Gauss white noise was superposed,and the low signal noise ratio ultrasonic wave was obtained with different denoising methods. The influence mechanism of cross correlation step length on stress evaluation was clarified with cross correlation coefficient theory. The results show that as cross correlation step length increases,the cross correlation coefficient function curve is more smooth and the maximum value increases gradually; the linear degree of relationship between the difference in time of flight and stress also increases; when cross correlation step length attains one cycle,cross correlation coefficient function curve and the curve of the difference in time of flight and stress overlap basically. The waveform distortion caused by noise is the main reason for the above results.
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