抄録
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.
