1995 Volume 44 Issue 500 Pages 663-668
The most effective means of ultrasonic defect sizing is considered to be the tip wave method. However, the intensity of the tip wave is very weak, and sometimes it prevents the use of tip waves. Several digital flaw detectors have been recently developed which are appropriate for use in the tip wave method, since they have rather low noise and more convenient functions of recordability and flexibility than the conventional analogue flaw detectors. The effectiveness of the full digital flaw detector HITACHI-DT-2000 has been described for the defect sizing of an artificial slit with round tip shape on a free surface. The newly developed model DT-2200 is greatly improved and almost noiseless, with a wide range of intensity of 100dB and very high resolution of 0.1mm. The sizing of five types of fatigue cracks is attempted here by using the result of numerical experiment. The knowledge obtained from the numerical experiment is proved to be very effective in discriminating several (multi-) tip waves generated in the reflection of ultrasonics by a fatigue crack. The technique is very easy and simple to use, but the accuracy of defect sizing is greatly improved at below 0.2mm: for the conventional analogue detectors, the accuracy is possible only at larger than 2mm. This level of accuracy will make it possible to estimate the defect sizing of fatigue crack, which is considered to be impossible by using ultrasonics. It is anticipated that this method will fill the gap and eliminate the distrust which has existed between ultrasonic testing and fracture mechanics.
