Photothermal models for lock-in thermographic evaluation of plates with finite thickness under convection conditions

Lock-in thermography is a technique which is increasingly being used for th e evaluation of relatively thin materials such as composite materials in ai rcraft structures. In such cases, the models available in the literature ca nnot accurately predict the difference in phase values between defective an d nondefective regions. This is because the models do not consider the conv ection conditions and the fact that the thickness of the sample is finite. This article proposes two models (a single-layer model and a multilayer mod el) to rectify this situation. The single-layer model was used to analyze t he thermal wave behavior in homogeneous media and the multilayer model was used to analyze the thermal wave behavior in inhomogeneous media. Based on the theoretical and experimental results, the influence of the combined hea t transfer coefficient was discussed. The results predicted by the models w ere consistent with that obtained experimentally. (C) 2001 American Institu te of Physics.