Observation of surface defects using photoacoustic microscope and quantitative evaluation of the defect depth

Quantitative trial of nondestructive evaluation (NDE) of a variable-depth defect using photoacoustic (PA) microscopy has been demonstrated. Two kinds of slit-type simulated defects! cross sections of which are rectangular and are-shaped, were fabricated on a metal specimen by electrical discharge processing. Imaging of defects by PA microscopy enabled precise determination of both the location of edges and the shapes of defects. PA imaging of an artificially made vertical defect with linearly increasing depth showed that the best result agrees well with a model based on a line heat source along a metal wall in a defect.