Nondestructive evaluation of tilted subsurface defects by photoacoustic microscopic imaging

In this study, the nondestructive testing (NDT) of tilted subsurface defects with a concave cross section was performed using a photoacoustic microscope (PAM). The tilted subsurface defects were formed in a metal plane specimen by mechanical processing. The obtained signal distribution was affected by the tilt angle of the subsurface defects, and the relationship between the gradient ratio and the tilt angle value exhibited a good correlation.