Infrared Thermography can be used to detect the subsurface defects in materials. This paper presents the results of Finite difference simulations of thermographs of (CFRP) Carbon Fiber Reinforced Plastics composite materials having Teflon inserts as defects. The inserts are assumed to be parallelepiped. The three dimensional parabolic heat conduction equation is solved and the temporal and spatial variation of signal and thermal contrast for defect situated at different depths are analyzed. The

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... detectability window of the defects in terms of the number of the harmonic in the Fourier Transform spectra (both amplitude and phase) is identified. It has been observed that the phase images give better understanding of the defects in the composites. Introduction Infrared thermography is widely used for the Non-destructive testing (NDT), (for the defect detection and characterization) of the multi-layered composite materials. The thermographic inspection of composite materials involves subjecting the specimen to a heat pulse for a short time and then analyzing the thermal response of the specimen under study. As the heat diffuses through the specimen, the defects contained in it causes perturbations in the heat flow which are revealed by the images of infrared camera. The acquired thermal images are processed using different signal processing techniques [1][2][3][4] [5] . The thermal images are acquired at a maximum frame capture rate of about 50 Hz frequency under experimental conditions such as non uniform heating, presence of different noise sources and anisotropic characteristics of specimen under study or the factors that limit the accuracy and repeatability of the data [6] [7] [8] . This paper presents the results of numerical simulations of Teflon inserts in carbon fiber reinforced plastic(CFRP) composites using finite difference method. It is aimed at identifying the optimum condition for defect detection which helps in overcoming some of the difficulties of experimental studies enumerated in the above paragraph. Also, knowledge of optimum condition of defect detection would help us in avoiding the repetition of the ex-periments. The paper is aimed at reporting the results of simulations of thermal NDT in-spection of CFRP laminate with Teflon inserts and the evaluation of the defect parameters for the sub surface defects. Modeling of the composite laminate with unidirectional fibers and the calculation of the temperature distributions in anisotropic composites done by implement-ing the finite difference method. A comparison of the numerical simulations with experimental images is made. Algorithm: The mathematical description of the problem is given by the fo llowing heat conduction equation in three dimensions.