D2D: A robust transient thermography NDT technique for real time in-field measurements

Not always during in-field measurements it is possible to reproduce laboratory conditions. This is especially true in thermography-based techniques which are most likely to be affected by unwanted external heat fluxes. Typical examples of parasitic heat sources (real or equivalent) may be spatial heater unevennesses, reflections, heater power variations in time, real external heat flux sources(sun, lamps, radiators, human beings, etc.), specimen curvature variation, misplacement of heater effects, etc. These heat sources contribute to reduce the overall SNR. As a consequence, a technique perfectly working in laboratory, when ported to field environment may not yield the expected results. Moreover the repeatability of the measurement is not ensured due to the randomness of these sources. D2D (Defect To Direction) is a transient thermography technique based on moving a linear heater (I-D) over a specimen's surface and recording the thermal evolution of the heated surface by means of a thermal imager. It's main specifications are: Insensitivity to some of the parasitic heat sources Decision-free operation (no skilled personnel required) Real time capability Large surface exploration capability Very low false call/missed defect probability. Tests on CFRP plates have been carried out. Results are reported.