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

Abstract

Lock-in thermography is a technique which is increasingly being used for the evaluation of relatively thin materials such as composite materials in aircraft structures. In such cases, the models available in the literature cannot accurately predict the difference in phase values between defective and nondefective regions. This is because the models do not consider the convection conditions and the fact that the thickness of the sample is finite. This article proposes two models (a single-layer model and a multilayer model) to rectify this situation. The single-layer model was used to analyze the 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 heat transfer coefficient was discussed. The results predicted by the models were consistent with that obtained experimentally.