New Sizing Technique of an Inclined Fatigue Crack on a Free Surface
The most effective means of ultrasonic defect sizing is considered to be the tip wave method.1,2 The intensity of the tip wave is very weak, and prevents the use of tip waves. However, a number of digital flaw detectors have recently been developed which are rather appropriate for use in the tip wave method, since they have rather low noise and have more convenient functions of recordability and flexibility than the conventional analogue flaw detector. The effectiveness of the full digital flaw detector HITACHI-DT-2000 has been described in the previous paper3 for the defect sizing of an artificial slit with a round tip shape, and with an inclination angles of up to 40° on a free surface. The newly developed model HITACHI-DT-2200 is greatly improved, as almost noiseless in itself with a wide range of intensity of 100 dB, and very high resolution of 0.1mm. We attempted the sizing of a natural fatigue inclined crack with a complicated shape, which is considered more difficult than the earlier simple shaped slit.3 The DT-2200 has unbelievable precision of below 0.03mm for 5MHz, and the accuracy of defect sizing is greatly improved at below 0.5mm: for the conventional analogue detector it is larger than 2mm. This remarkable accuracy is possible because of the accuracy of the DT-2200, and the knowledge obtained from computer simulation as described in the previous paper.3
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