A new enhanced optical technique for NDI has been developed at IAR/NRC. This technique converts changes in surface slope into light intensity changes in an image created with a computer based line scanner. Light passing through a slit (edge of light) is reflected from the inspected surface at a shallow angle and captured by the scanner detector. Typically a plastic zone exists in the vicinity of a crack. This zone leaves a deformed surface trail along a crack. It is this surface deformation which is enhanced by the edge of light method. In this study, a prototype edge of light scanner was used to inspect low cycle fatigue cracks in engine disk bolt holes. The results showed surface breaking cracks which were not visible using optical microscopy. The probability of detection of the inspection was calculated by opening the cracks. The prototype edge of light scanner performed significantly better than liquid penetrant and magnetic particle techniques for this application. The ability of this technique to enhance very small scale surface deformation holds promise for may NDI applications and will be the subject of future studies and evaluations.

Date Published: 14 November 1996
PDF: 11 pages
Proc. SPIE 2945, Nondestructive Evaluation of Aging Aircraft, Airports, and Aerospace Hardware, (14 November 1996); doi: 10.1117/12.259091

Published in SPIE Proceedings Vol. 2945:
Nondestructive Evaluation of Aging Aircraft, Airports, and Aerospace Hardware
Raymond D. Rempt; Alfred L. Broz, Editor(s)