Study on Detection and Quantitative Evaluation of Fatigue Cracks Using Surface SH Waves(NDE2)

Abstract

Nondestructive evaluation of a surface slit and a fatigue crack by surface SH waves has been studied. By adjusting incident angle of SH waves probe, surface SH waves passing through the surface region of materials are received. In this study, diffraction of surface SH waves received by double-probe technique was used. Firstly, the specimens introduced surface slit were inspected by surface SH waves. With the results that the amplitude of surface SH waves decreased with the increment of slit depth in the depth over half wavelength of SH waves, but the amplitude is constant in the depth under half wavelength of SH waves. On the other hand, the arrival time of surface SH waves increased with the increment of slit depth in every depth. Furthermore, the changes of the amplitude and the arrival time to the increment of slit depth were calculated based on Fresnel-Kirchhoff diffraction integral. A comparison between the measured values and the calculated ones shows that the change of the arrival time is useful for evaluating surface defect. Secondly, the evaluation method of a fatigue crack in the round bar using the artificial circle osculating fatigue crack was proposed, and the growth behavior of fatigue crack, which initiated at an artificial small hole by rotating-bending fatigue, was evaluated with the change of the arrival time. By applying the evaluation results to Paris' law, the validity of our method was confirmed.