349 低サイクル疲労微小表面き裂の超音波非破壊評価 : 検出限界と周波数の関係(OS2-1 欠陥検出)(OS2 超音波と材料評価)  [in Japanese] 349 Ultrasonic Non-destructive Testing of Low-cycle Fatigue Small Surface Crack : Relation between Frequency and Detection Limit  [in Japanese]

This present study was done with the aim of improving the reliability of quantitative ultrasonic nondestructive testing. The water immersion ultrasonic method, using an oblique longitudinal wave with large incidence angle (over the critical angle), was applied to measure small surface fatigue crack due to low-cycle loading. Surface fatigue crack initiation process, beginning from persistent slip band initiation, was measured using ultrasonic microscope. To estimate the precision of measurement, four transducers with different frequency, they are 5,10,20 and 50MHz, respectively, were used to make clear the relation between the ultrasonic frequency and its minimum detectable size of surface fatigue crack.