Study on wavelet-based crack detection in pipes using ultrasonic longitudinal guided-wave

Using the LS-DYNA970 dynamic commercial finite element program, the numerical simulations of the transonic longitudinal guided-wave in cracked pipes are conducted, in which the effect of transverse strains has been taken into consideration. The influence of the excitation frequency on the frequency dispersion of guided waves is analyzed. By choosing proper scale and basic functions of wavelets, the weak signals of defect detection are identified, which cannot be observed directly. Meanwhile, the distribution of the noise in the detection signals is discussed by time-frequency analysis. And the crack identification in the low signal-noise ratio is realized based on the algorithm of wavelet decomposition and reconstruction.