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Proceedings Paper

Thermographic imaging of cracks in thin metal sheets
Author(s): K. Elliott Cramer; William P. Winfree; Patricia A. Howell; Hazari I. Syed; Keith A. Renouard
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Paper Abstract

The presence of cracks significantly decreases the structural integrity of thin metal sheets used in aerospace applications. Thermographic detection of surface temperature variations due to these cracks is possible after external heating. An approximate line source of heat is used to produce an inplane flow of heat in the sheet. A crack in the sheet perturbs the inplane flow of heat and can be seen in an image of the surface temperature of the sheet. An effective technique for locating these perturbations is presented which reduces the surface temperature image to an image of variations in the inplane heat flow. This technique is shown to greatly increase the detectability of the cracks. This thermographic method has advantages over other techniques in that it is able to remotely inspect a large area in a short period of time. The effectiveness of this technique depends on the shape, position and orientation of the heat source with respect to the cracks as well as the extent to which the crack perturbs the surface heat flow. The relationship between these parameters and the variation in the heat flow is determined both by experimental and computational techniques. Experimental data is presented for through-the-thickness, subsurface and surface EDM notches. Data for through-the-thickness fatigue cracks are also presented.

Paper Details

Date Published: 1 April 1992
PDF: 9 pages
Proc. SPIE 1682, Thermosense XIV: An Intl Conf on Thermal Sensing and Imaging Diagnostic Applications, (1 April 1992); doi: 10.1117/12.58532
Show Author Affiliations
K. Elliott Cramer, NASA/Langley Research Ctr. (United States)
William P. Winfree, NASA/Langley Research Ctr. (United States)
Patricia A. Howell, Analytical Services & Materials, Inc. (United States)
Hazari I. Syed, Analytical Services & Materials, Inc. (United States)
Keith A. Renouard, Baylor Univ. (United States)

Published in SPIE Proceedings Vol. 1682:
Thermosense XIV: An Intl Conf on Thermal Sensing and Imaging Diagnostic Applications
Jan K. Eklund, Editor(s)

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