Signal reconstruction with infrared thermographic data in the application of rail defect detection

Thermographic techniques are widely used to characterise material damage, porosity and moisture in structures. Due to the thermographic signal reconstruction (TSR) technique, active thermography has made significant progress. In this study, the TSR technique was applied to identify a rubber layer that mimics an internal defect, which is attached to the back of the steel plate, after a 1.0 min thermal stimulation. The peaks of the first and second derivative logarithmic curves correspond to the important time point revealing the position of the attached flaw. Furthermore, a new post-processing technique for infrared thermographic data was proposed by exploiting polynomial orders of the fitting curves to produce a synthetic image, which can highlight the flaw with distinctive contrast. Finally, the upgraded TSR technique was applied to image a natural shelling defect in a rail sample with an excellent contrast.