Analysis of long-pulse thermography methods for defect depth prediction in transmission mode

Defect depths are estimated in basalt fiber reinforced composite using long-pulse infrared thermography in the transmission mode. Defects of different sizes and depths are induced in the basalt fiber composite using flat-bottomed holes and their thermograms are analyzed. The contrast derivative and Parker's method are used to predict the defect depths. The proportionality factor between peak contrast time and defect depth is determined analytically for the contrast derivative method. It is observed that the contrast derivative method predicts the defect depths and is independent of the defect sizes, whereas Parker's method predicts deeper depth. The experimental results are in good agreement with the numerical results.