Abstract
In this study, an ultrasonic technique for quantitative nondestructive evaluation of a small surface fatigue crack was developed. The use of an oblique longitudinal wave with large angle (over the critical angle) of incidence upon a specimen surface was emphasized. Ultrasonic testing was performed for a specimen with small surface fatigue cracks and artificial defects. We have used maximum amplitude of reflection echo due to these defects as a parameter, to evaluate them quantitatively. From such measurements, we have concluded that with the use of this parameter, surface fatigue cracks with more than 115µm of surface length can be detected. Simultaneously, crack depth and deflection can also be detected. Based on these experimental results, we have proposed a set of experimental equations to evaluate the surface length and depth of crack. Finally, a model based on three-dimensional elastodynamics was proposed to simulate this ultrasonic technique, and numerical analysis was performed for the surface crack reflection problem.
