Observation of complicated surface defects by photoacoustic microscopy and nondestructive evaluation

Simulated complicated surface defects fabricated on a metal specimen are detected by photoacoustic (PA) microscopy, and their signals are reconstructed as PA images. Two types of complicated defects with slit-type cross sections were fabricated on a metal specimen by electrical discharge processing and mechanical processing. The surface defect geometry of one type is a pair of mutually parallel defects, and that of the other type is a pair of defects which cross each other orthogonally. The PA image obtained, clearly shows the locations of the edges of the two defects. Furthermore, the results show that complicated defects composed of two sections can be detected separately as individual defects, and that the photoacoustic method is useful for detection of crossing surface defects which are difficult to detect using present NDE techniques.