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Proceedings Paper

Thermographic measurement of thermal barrier coating thickness
Author(s): Steven M. Shepard; Yu Lin Hou; James R. Lhota; David Wang; Tasdiq Ahmed
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Paper Abstract

Flash thermography is widely used to inspect Thermal Barrier Coatings (TBC) during manufacturing and maintenance for defects such as delamination or contamination. However, attempts to use thermography to quantify TBC thickness have been less successful. In conventional thermographic NDT applications, the sample surface is opaque to an incident light pulse, and highly emissive in the infrared. The situation is more complex in TBC's, as the coatings are translucent to visible light and near-IR radiation (including the IR component of the flash). Furthermore, TBC's are translucent to the mid-IR wavelengths at which many IR cameras operate. Thus, in the absolute worst case, the flash pulse does not heat the coating, and the camera does not see the coating. Although the latter problem can be mitigated by judicious choice of camera wavelength, it must also be recognized that both the heating and cooling mechanisms in a flash-heated TBC are different from the usual thermography model, where transit time of a heat pulse from the sample surface to a layer interface is an indicator of coating thickness. The resulting time sequence is processed using the Thermographic Signal Reconstruction to generate thickness maps which are accurate to an accuracy of a few percent of the actual coating thickness.

Paper Details

Date Published: 28 March 2005
PDF: 4 pages
Proc. SPIE 5782, Thermosense XXVII, (28 March 2005); doi: 10.1117/12.606124
Show Author Affiliations
Steven M. Shepard, Thermal Wave Imaging, Inc. (United States)
Yu Lin Hou, Thermal Wave Imaging, Inc. (United States)
James R. Lhota, Thermal Wave Imaging, Inc. (United States)
David Wang, Thermal Wave Imaging, Inc. (United States)
Tasdiq Ahmed, Thermal Wave Imaging, Inc. (United States)

Published in SPIE Proceedings Vol. 5782:
Thermosense XXVII
G. Raymond Peacock; Douglas D. Burleigh; Jonathan J. Miles, Editor(s)

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