Evaluation of Start of Crack Growth of Nuclear Material (SUS316NG) using Ultrasonic

The detection of small fatigue cracks is of particular interest because it is a key element of remaining life prediction. In the present study low cycle fatigue crack initiation in austenitic stainless steel (SUS316NG) subjected to plane bending is observed and compared the change of back-reflection intensity of ultrasonic wave using the scanning acoustic microscope. Ultrasonic data is recorded as a function of the number of cycles and compared with slip band length measured optically. Surface observation using optical and scanning acoustic microscopy revealed that with increasing the number of fatigue cycle the slip band density increased and the amplitude of back reflection intensity gradually decreased before the slip band length increases. Due to the cyclic loading, dislocation density along persistent slip bands increase. The attenuation of ultrasonic back reflection intensity is due to the dislocation damping and this mechanism was considered.