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Proceedings Paper

Quantification of defect size in shearing direction by shearography and wavelet transform
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Paper Abstract

Shearography is a recognized interferometric technique in non-destructive testing to detect defects. Defects are detectable in wrapped phase maps because they are characterized in their neighborhood by singular fringes. They are detectable in unwrapped phase maps, because they induce unexpected phase values. By analyzing the length of unexpected phase values area in shearing direction, and by taking into consideration shearing amount, defect size can be locally estimated. To examine this length, we propose to locally determine borders of unexpected phase values region by analyzing wavelet transform of unwrapped phase map profiles. The borders of defect area are found by examining the convergence at fine scales of lines of wavelet modulus maxima. To have a physical interpretation of this convergence, second derivate of a Gaussian is employed as mother wavelet: estimated borders of defect region are some maximal curvature points of unwrapped phase map profile. To finish, we show that shearing amount does not affect estimated defect size with our methodology. So, shearography is adapted to quantify defects in shearing direction. Currently, in any other direction, an ambiguity exists on the position where the local estimation of defect width is performed. The methodoly cannot be employed.

Paper Details

Date Published: 18 June 2007
PDF: 10 pages
Proc. SPIE 6616, Optical Measurement Systems for Industrial Inspection V, 661636 (18 June 2007); doi: 10.1117/12.725997
Show Author Affiliations
Fabrice Michel, DEIOS s.a. (Belgium)
Univ. de Liège (Belgium)
Vincent Moreau, DEIOS s.a. (Belgium)
Vanessa Rosso, Univ. de Liège (Belgium)
Serge Habraken, Univ. de Liège (Belgium)
Bernard Tilkens, DEIOS s.a. (Belgium)

Published in SPIE Proceedings Vol. 6616:
Optical Measurement Systems for Industrial Inspection V
Wolfgang Osten; Christophe Gorecki; Erik L. Novak, Editor(s)

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