Application of wavelet transform to damage detection of circular cylindrical shells

Research on detection in pipes is of major importance to the oil and chemical industries. Early detection and quantification of damage extent can reduce costs incurred due to wear on the machinery and maintenance of the pipes. Ultrasonic testing is one of the most widely used nondestructive evaluation techniques in engineering practice, which potentially provide an attractive solution to this problem because they can be excited at one location on the structure and will propagate many meters, however, guided wave testing is complicated by the presence of many possible wave modes, most of which are disperse. Therefore, it is desirable to develop more reliable, accurate, and robust ultrasonic nondestructive methods to detect these cracks before catastrophic failure occurs. In this paper, the wavelet transform and the tone burst of 10 cycles modulated by HANNING window are employed. We concentrate on the wavelet transform in order to enhance the sensitivity of damage detection. Wavelet analysis applies a windowing technique with variable-sized regions and allows the use of long time intervals where we want more precise low-frequency information, and shorter regions where we want high-frequency information. Furthermore, it is capable of revealing aspects of data that other signal analysis techniques missed aspects like trends, breakdown points, discontinuities in higher derivatives, and self-similarity. Features for discrimination of detected signals are extracted in time domain, spectral domain and discrete wavelet representation. Finally, the discrete wavelet transform is applied to the damage detection of circular cylindrical shells. The simpleness and accuracy of the proposed method make it attractive in practical damage monitoring application.