NDTnet 1998 Aug, Vol.3 No.8

Abstract

Defect detection is a very critical but mandatory job in the aeronautical industry; the ideal tool or technique must be reliable, in the sense of not leaving any area of defect unrevealed, fast and not costly. Optical NDT techniques like holography, speckle and shearography are suited candidates for this application because they are very sensitive, full field imaging and now mature instruments.
In particular our laboratory experienced very good results in applying shearography, that is an interferometric recording of two images of the object laterally sheared, to real parts of AGUSTA helicopters, dynamically loaded. Vibrational loading, with respect to more traditional thermal and vacuum loading, is more reliable related to thermal because the part under test doesn't maintain any memory of the previous loadings and far more easily applicable than vacuum.
Moreover, after the tests carried-out employing a shaker, the aim is to use the free running condition of the helicopter itself as a kind of natural stress. In fact, due to a modular semiconductor laser source, we can cover surfaces from tens of centimeter square to some meter square, per single acquisition.

We will present results obtained on both thin layers and honeycomb structures presenting disbondings, delaminations and impact damages. The picture shown in the following presents the common appearance of the defect over the undamaged surrounding area. During the presentation of this activity it will also be shown a videotape related to a test performed on a real helicopter tail in a hangar. We intend to demonstrate that optical techniques can now be considered reliable and profitable about the time needed for the test and hence about costs, not forgetting also the absolute non invasivity and the very light level of stress to be applied.

Fig.: Defect in composite panel under vibrational load.

References:
1. Hung, Y.Y., Optical engineering, 1982, 31, 4: 391. 2. Newman, J. W., SPIE vol.2455, 210.

Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00

Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:

Publication Contact:
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