Optics & Laser Technology 37 (2005) 509–512 Research Note Thermally induced deformations measured by shearography K. Habib à Materials Science Laboratory, Department of Advanced Systems, Kuwait Institute for Scientific Research (KISR), P.O. Box 24885, Safat 13109, Kuwait Received 14 March 2003; received in revised form 5 December 2003; accepted 16 June 2004 Available online 13 August 2004 Abstract In the present work, the thermo-mechanical behavior, temperature versus thermal deformation with respect to time, of different coating films were studied by a non-destructive technique (NDT) known as shearography. Organic coatings, i.e., Epoxy on metallic alloys, i.e., carbon steels, were investigated at a temperature range simulating the severe weather temperatures in Kuwait especially between the day-time and the night-time temperatures. The investigation focused on determining the in-plane displacement of the coatings, which amounts to the thermal deformation and stress with respect to temperature and time. Along with the experimental data, a mathematical relationship was derived describing the thermal deformation and stress of a coating film as a function of temperature. Furthermore, results of shearography indicate that the technique is a very useful NDT method not only for determining the thermo-mechanical behavior of different coatings but also can be used as a 2D microscope for monitoring the deformation of the coatings in real-time at a microscopic scale. r 2004 Elsevier Ltd. All rights reserved. Keywords: Shearography; Optical interferometry; Thermal stress; In-plan displacement; High temperatures; Organic coating 1. Introduction It is well established that metrological methods of coherent lights such as speckle interferometry are found very useful in measuring deformation at surfaces of different objects in various conditions [1]. However, none of the coherent light techniques have been utilized for determining the thermo-mechanical behavior of different coatings at metallic samples thus far. In fact, Zhang [2] was the first to apply the technique of speckle shearing interferometry, shearography, for measuring of residual stresses in solid metals. The technique of Zhang was based on drilling a hole in a stressed solid metal in order to measure the localized surface relief in the metal. As a consequence, one may speculate the possibility of applying the technique of shearography for evaluating thermo-mechanical beha- vior, and determination of thermal stress and strain, as a function of temperature and time, of different coatings due to surface relief by a localized heat impingement. In this investigation, procedures of determination of the thermo-mechanical behavior of various coatings are described. 2. Theoretical analysis In speckle metrology, it is well known that an interferogram of an object normally results from two speckle wave fronts nearly superimposed but having slightly phased shift because of the deformation which usually takes place at the object surface between the first and second exposure. In the case of measuring surface relief of a coating, which associated with localized heat impingement, of an area A h , at the coating surface, consider a metal substrate has surface area, A, covered by either an organic or a ceramic coating. The ratio of the area of heat impingement to the total area of the ARTICLE IN PRESS www.elsevier.com/locate/optlastec 0030-3992/$-see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.optlastec.2004.06.007 à Tel.: +965-543-0228; fax: +965-543-0239. E-mail address: khaledhabib@usa.net (K. Habib).