Reconstruction of Simulated Cylindrical Defects in Acrylic Glass Plate Using Pulsed Phase Thermography

The results of testing of acrylic glass, in which cylindrical defects were simulated at different depths by applying Pulsed Phase Thermography, are presented in the paper. To ensure better visibility of the simulated defects, suitable thermal images were selected and then processed by using two different procedures. In the first procedure, reduced thermal image sequences were generated by uniform extraction from the basic sequence, to enable analysis at different sampling frequencies. The second procedure was based on the application of a window function, which ensured that only uniformly selected thermal images took part in the evaluation of the basic sequence. The remaining thermal images were not used, but they did participate in the determination of the length of the analyzed sequence; in other words, their existence was registered through the number of samples used in Fast Fourier Transformation. The second procedure yielded much better results with regard to the estimation of the shape of a defect and the depth at which it was located. To provide better insight into the development of the thermal process in the defect area, an additional analysis of pixel intensity variation in the time domain was undertaken.