Absolute peak slope time based thickness measurement using pulsed thermography

Several methods have been reported in the literature using pulsed thermography for quantitative measurement of defect depth or sample thickness. In this paper, based on the analysis of a theoretical one-dimensional solution of pulsed thermography, we proposed to use the absolute peak slope time (APST) for quantitative measurement of defect depth. APST is the peak slope time of the curve which is obtained by multiplying the original temperature decay with the square root of the corresponding time. The theoretical model shows that APST has linear relation with square of defect depth, which was verified with the experimental results of an aluminum and a steel specimen with six flat-bottom wedges and holes as simulated defects respectively.