Photothermocapillary diagnostics of near-surface flaws in a solid under a varnish-and-paint coating

A new photothermal method of nondestructive testing is proposed and implemented for specimens having horizontal planes. It is shown that a near-surface flaw can be detected under a varnish-and-paint coating by the difference of the heat resistances in the flaw zone and its vicinity, which causes a change in the thermocapillary response of a silicon-oil layer coating the surface of the article. A decrease in the diameter of the scanning beam and an increase in its power cause an increase in the amplitude of the scanning curve and its slope near the flaw boundary.