抄録
Accurate crack sizing in the structures is important for insuring structural reliability. Ultrasonic TOFD (Time-of-flight Diffraction) method is one of the most accurate crack sizing methods. However, the method is not applicable to thick austenitic stainless steels due to the amplitude of the crack tip diffraction echo being weak, and that this weak echo is attenuated in thick materials. In this study, in order to improve both S/N ratio and time resolution of TOFD signals, the usefulness of pulse compression technique is examined. We compared the result with the ordinary TOFD method which uses spike pulse as an incident wave, and we found that the S/N ratio of the compressed pulse was higher than the ordinary method. The sizing accuracy of proposed method was similar to the traditional method. Finally, we conducted the wavelet transform of the compressed pulse. The frequency components of the echoes used for sizing were different, and this feature can be used for signal type classification during crack sizing.
