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NDE of a variable-depth crack by photoacoustic imaging

A new photoacoustic (PA) QNDE scheme based on PA signal dependence on crack depth has been investigated. Two kinds of slit-type simulated cracks, the cross-section of which are a rectangle and an arc, are fabricated on a metal specimen by electrical discharge processing. Imaging of cracks enables precise determination of both the location of edges and the shape of the crack. To verify the PA signal dependence on crack depth, PA imaging of an artificially made vertical crack with linearly increasing depth is performed and the result agrees well with a simple model based on a line heat source along metal walls in the crack.