The combinaison in a unique system of an infrared sensor and a laser as excitation source is called a photothermal camera. The images are obtained thanks to a video scanning of the excitation and dectection spots on the surface of the-piece to test: the generation of tranverse heat fluxes in the material leads to the detection of surface-breaking cracks defects.With those cameras, the main encountered problem is the poor discrimination between the cracks and the signals produced by the topographical and optical defects present in the inspected area, especially in the case of bare metallic surfaces.
The new photothermal camera presented in this paper contains an original device which simultaneously leads to a strong attenuation of the signals produced by local optical variations, and to an increase of the thermal contrast produced by the cracks.
This camera has been tested for the detection of true defects in order to compare its sensitivity to the one of penetrants (see figure below): the smallest cracks, observed on rough stainless steel samples, have openings smaller than 1 µm. Such performances permit to consider that this apparatus is an interesting alternative to the conventional NDT methods (penetrants, eddy currents, magnetics ... ) for fast and remote surface damages detection.
 Fig. Crack (width 5 µm) at the (rough) surface of a steel piece: new photothermal camera versus |
Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00
Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:
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