The detection and characterisation of fatigue cracks growing radially from fastener holes continues to be a major problem in the non-destructive inspection of aircraft. In general, it is highly desirable to be able to detect cracks in the skin and sub-structure without the need to remove fasteners. Eddy-current methods are in principle well-suited to the detection of cracks in metals but, in this case, difficulties of interpretation can arise as a consequence of the relatively complicated geometry. For example, the effect of the fastener itself or a nearby edge can easily mask the effect of a crack. If the effects of irrelevant geometric features can be identified and removed then the ability of eddy-current systems to detect cracks reliably under these circumstances can be considerably enhanced. An intelligent eddy-current instrument has been developed specifically for this problem. The Eddiscan uses a rotating transducer to map precisely any variations in the induced electromgnetic field around the circumference of the fastener. By using pattern recognition and other analysis techniques, the presence and position of cracks can then be inferred. Using this method, cracks in the skin and sub-surface layers can be detected with either ferrous or non-ferrous fasteners installed.
Progress in the detection of cracks under installed fasteners using eddy currents
Fortschritt bei der Rißerkennung unter montierten Befestigungselementen mit Hilfe von Wirbelströmen
1990
8 Seiten, 8 Bilder, 3 Quellen
Conference paper
English
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