QNDT of surface tilt defects by photoacoustic microscopic imaging

In this study, basic experiments on quantitative nondestructive testing (QNDT) of simulated surface tilt defects using a photoacoustic microscope (PAM) have been demonstrated. The specimens used in the experiments were pure aluminum plates. The surface tilt defect was introduced into the specimen by mechanical processing. The photoacoustic (PA) measurements were carried out by changing the modulation frequencies. The obtained signal strength distribution was affected by the tilt angle of the surface defects. By defining the "degree of asymmetry' as the ratio of the difference between two peaks of phase signal distribution to the height of their mean value from the background, the correlation coefficient between tilt angle and the degree of asymmetry showed the value of 0.997.