NEW TECHNIQUE OF DEFECT SIZING OF A SMALL INCLINED CRACK ON A FREE SURFACE USING MULTI-TIP-WAVES

Abstract The most effective way of ultrasonic defect sizing currently recognized is the tip echo method, and it has broad and practical applications. Tip waves have very weak intensity, about 20 dB lower than the mean echo, and this prevents their use in many instances. Recently, low noise full digital flaw detectors have been developed, which make it very easy to catch tip waves. In the reflection by a small crack, we are now able to catch several tip waves easily in one shot. Moreover, the distances between two tip echoes are more stable for the fluctuation of experimental condition than the conventional method. Thus giving us more information than by the conventional method. Numerical experiments must be used, in order to distinguish each tip echo. As a first step, experiments using the full digital flaw detector DT-2000 were conducted, and several tip echoes were obtained with the main echo for reflections by an artificially inclined small crack on a free surface. The crack height is 1.5 mm, the inclination angles are 10° to 40° degrees. Incident waves of 45 degrees are given from both sides of the crack. Crack height and inclination angles are estimated from the distance of each echo in one experiment, derived from the theoretical equation and numerical experiment. The results show very good agreement with actual values. In the reflection of ultrasonics, many tip waves are generated from the tip or comer of a defect. These are ignored simply as noise in the conventional method, but complete evaluation of defect size can be obtained by the full use of these tip waves.