DETECTABILITY OF KNOWN CRACKS UNDER FASTENERS USING ULTRASONIC IMAGING

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Authors
  1. Nolan, R.W.
  2. McRae, K.I.
Corporate Authors
Defence and Civil Inst of Environmental Medicine, Downsview ONT (CAN)
Abstract
The detection of fatigue cracks under installed fasteners in aircraft structures has been an area of concern for many years. This paper describes results obtained using a 70 degree angle of incidence ultrasonic shear wave technique to systematically inspect countersunk fastener holes in aluminum plates with simulated fatigue cracks of known dimensions and locations. Holes were inspected with ferrous and titanium fasteners installed as well as without fasteners. It was concluded that this technique was readily able to detect a variety of fatigue cracks in holes both with and without fasteners installed. The smallest crack detected was 0.006", although most cracks were greater than 0.010" and some crack dimensions were as large as 0.25". Although it was shown that this technique was capable of detecting the presence of relatively small cracks, it is not directly applicable to field use. It is an immersion technique and requires 15-20 minutes per scan, making it impractical for inspecting large numbers of holes. It is possible, however, that current on-aircraft scanning capabilities could be modified in order to use this procedure.
Keywords
Nondestructive inspection;Cracks under fasteners;Fatigue cracks;Shear wave;Ultrasonic shear wave;Ultrasonic imaging
Report Number
DCIEM-98-TM-08 — Technical Memorandum
Date of publication
01 Feb 1997
Number of Pages
18
DSTKIM No
98-00689
CANDIS No
507514
Format(s):
Hardcopy;Document Image stored on Optical Disk

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