Abstract
Photo acoustic images of coated steels degraded under cyclic corrosion tests were obtained by scanning a chopped and focused Laser beam and detecting the heat wave, which was produced by the beam, at the opposite side of the incidence. Amplitude of the signals was decreased and phase shift (time lag) of the wave measured with the incident beam was increased at the points where the delamination or under film corrosion occurred. The width of the delamination or the under film corrosion from the scribes of the coating was quantitatively evaluated, and it increased with the duration of the tests. The size and the area ratio of blisters formed around the scribes were also determined by this method. The spatial resolution of the images was achieved to 20 μm and discussed related to the measurement conditions, such as chopping frequency.
