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The Defect Depth Characterization Using Pulsed Thermographic Data

Defects in material can be fully described if their shape and position is determined. Our previous research was focused on composites and flood lamps as a heat source. The focus in presented research is on metals and Xenon flash lamps. The main aim of this research is to estimate the depth of detected damage. The infrared camera is used for capturing temperature development on the surface of an aluminum sample in time. Contrary to the Lock- in thermography, where several acquisitions are needed, for the Pulse Phase Thermography (PPT) the depth of defect can be revealed from single acquisition of cooling sequence. As shown in previous work, thermal decay curve of every pixel can be reconstructed as a convolution of sinus functions by applying the Fourier transform (FFT). The method was applied to the aluminum sample, the flat plate with flat bottom milled holes of different depths representing defects. The determination procedure for the coefficient of thermal diffusivity and blind frequency is demonstrated. Measured and estimated values were compared for each depth, including the regression analysis.

Infrared thermography, Nondestructive testing, Depth Characterization, Numerical model

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