Infrared Thermography, as one of the NDT methods, uses the observations of the temperature distribution on the sample surface for purposes of subsurface defect detection. Defect detection is based on the different temperature signature that the surface above the defective area shows with respect to the non-defective sample regions. In the pulse thermography experimental procedure, short and strong heat pulses are used as the excitation source. Energy delivered to the sample surface is then transferred from the surface towards the sample interior and partly dissipated to the environment. Different thermal properties that the sample and the defect inside the sample have are the reason why different heat transfer conditions inside the sample occur in the defective and non-defective sample regions. As a result, the above mentioned temperature distribution differences appear on the sample surface and are used as the base for defect detection and characterization.

Over the years numerical modeling has become increasingly popular. The Finite element method (FEM) has become a useful and often employed tool in many complex physical problem analyses. Once established and validated with experimental results, FEM models provide a low-expense alternative to additional experiments.

In the case of pulse thermography, the idea is to apply FEM modeling to tested samples. First the model results need to be compared and verified with the experimental results in order to confirm the model validity. At the same time, parameters used in the model (such as material properties, heat transfer conditions, size, position and type of the defect) represent the characteristic properties of the physical model under consideration - the tested sample subjected to the given experimental conditions. Changing parameters of the model (defect position, size or properties) and repeating the simulation provides the results that could be expected if another sample corresponding to the new model is to be tested.

Finally, the idea is to proceed with the defect characterization based on correspondence between the results of the experiment performed on another similar specimen and the results obtained for a larger number of simulations with different input model parameters.

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