Qualitative and Quantitative Assessment of Steel Plates Using Pulsed Phase Thermography

摘要

Pulsed phase thermogmphy has been proven effective on depth retrieval of flat bottomed holes in materials such as plastics and aluminum. In pulsed phase thermography, amplitude and phase delay signatures are available following data acquisition, by applying a transformation algorithm such as the Fourier transform on thermal profiles obtained by pulsed thermography. following earlier work by two of the authors (an extended review on pulsed pliase thermography theory including a new inversion technique for depth retrieval by correlating the depth with the blind frequency f_b [frequency at which a discontinuity produces enough phase contrast to be detected]), in this paper, steel plates containing flat bottomed holes at different depths (from 1 to 4.5 mm [0.04 to 0.18 in.]) were tested by quantitative pulsed phase thermography. Least squares regression results showed excellent agreement between depth and the inverse square root blind frequency, which can be used for depth inversion. Experimental results on steel plates with simulated corrosion are also presented. It is worth noting that, in some cases, results were improved by performing pulsed phase thermography on reconstructed (synthetic) rather than on raw thermal data.