QNDT of complicated surface-subsurface defects and imaging of real pitting corrosion by photoacoustic microscopy

We performed quantitative nondestructive testing (NDT) of simulated complicated surface-subsurface defects and imaged real pitting corrosion using photoacoustic microscopy. Two types of complicated surface-subsurface defects were fabricated in pure aluminum plate specimens in the first experiment: one was a complicated defect that combined a pinhole surface defect with an internal cylindrical defect; the other was a complicated branched defect that combined a vertical slit-type surface defect with a subsurface defect perpendicular to the surface defect wall. A specimen with an isolated subsurface defect was prepared for comparison. The surface and subsurface parts of the defect were distinguishable in photoacoustic (PA) amplitude and phase images obtained by a PAM. In the second experiment, pitting corrosion was prepared on the surface of aluminum plates in aqueous alcohol solution. PA measurements of real pitting corrosion were carried out and the results were consistent with the results using simulated pitting corrosion.