Simulations of the interaction of So Lamb mode with a corroded area allow us to explain the remarkable sensitivity of S0 to corrosion pitting. They highlight that a mode conversion occurs at corrosion pitting between the S0 and A0 modes. This mode conversion is enhanced by the antisymmetric geometry of corrosion pits and by the proximity of S0 and A0 dispersion curves. Nevertheless, this mode conversion between S0 and A0 is also observed for a thickness variation. But in this case, another mode A0 which is not produced in the corroded case appears. So according to numerical predictions, the apparition of A0 caused by mode conversion on suspect area reveals corrosion pits whereas the apparition of both A0 and A1 Lamb modes is characteristic of a thickness variation. Experimental investigations correspond well with the predictions and highlight the mode conversion produced by corrosion pits between S0 and A0. In addition, results show that it is more convenient to monitor the apparition of A0 produced by mode conversion on the corroded area rather than to measure the attenuation of S0. This new processing of the experimental data improves meaningfully the sensitivity of this nondestructive technique to early corrosion. Moreover, as expected by predictions, the monitoring of the apparition of A0 permits also to discriminate a thickness variation from a slightly corroded area. So, the recognition of mode conversions produced by a suspect area allows us to avoid false alarms. The main advantage of this new monitoring method is its remarkable sensitivity to very early corrosion pits and the possibility to discriminate a thickness variation from a fine corroded area. This technique is now sensitive to few corrosion pits distributed on a square centimeter of an aluminum plate. Nevertheless, corrosion at an early stage and localized on a thickness variation can not be detected by exploiting this method because of the confusion between the mode conversions produced by the thickness variation and by the corrosion pits. On a thickness variation, just the strongly corroded areas will be detected by measuring the attenuation of the wave packet transmitted by the damaged region.
Optimization of hidden corrosion detection in aircraft structures using Lamb waves. Numerical predictions and experimental results
Optimierung des Nachweises verdeckter Korrosion in Flugzeugstrukturen mittels Plattenwellen. Numerische Vorhersage und experimentelle Ergebnisse
2007
8 Seiten, 9 Bilder, 7 Quellen
Aufsatz (Konferenz)
Datenträger
Englisch
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