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14. Laser-ultrasonic detection of hidden corrosion in aircraft lap joints: Results from corroded samples.

Author

Choquet, M., Le´vesque, D., Massabki, M., Ne´ron, C., Bellinger, N. C., Forsyth, D., Chapman, C. E., Gould, R., Komorowski, J. P., and Monchalin, J.-P.

Subjects
ULTRASONIC testing, LASERS, CORROSION & anti-corrosives, AIRPLANES
Abstract

The detection of hidden corrosion has been recognized as a serious problem in the maintenance of aging aircraft structural elements such as lap joints. In the presence of corrosion, the thickness of the metal skin may be significantly reduced and reach a level (generally above 10% of metal loss) that requires repair or replacement. The Industrial Material Institute (IMI) has developed a novel method that uses the spectral analysis of laser-ultrasonic waveforms to determine the residual metal skin thickness of the top skin of a lap joint. Previous work has shown that a characteristic equation can be derived that predicts the resonance frequencies of a paint-metal structure, such as encountered in an aircraft lap joint. Using numerical minimization techniques, this expression is used to process the laser-ultrasonic data and produce thickness maps of both the paint layer and the metal skin of a lap joint. Results from standard samples with flat-bottom holes show that the laser-ultrasonic technique can detect metal loss below 1% of the nominal thickness value of the metal skin. Results from corroded samples demonstrate the same detection level as for flat-bottom hole samples. Comparison to X-ray images shows that the laser-ultrasonic method gives a thickness map that has the same accuracy as the X-ray system without the need of dismantling the sample. These results indicate that laser-ultrasonics could be a useful tool not only to inspect aircraft during routine maintenance but also to provide valuable data in the study of corrosion inception and growth in lap joint structures. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Published
2001

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