The aim of the study is to develop a quantitative understanding of the transient thermography imaging process. It includes development of experimental procedure and system characterisation such as averaging for noise reduction; correction for uneven heating and modulation transfer function (MTF) assessment. A detailed study has been made of the characteristics of the transient thermal images formed by back drilled holes artificial defect of different diameters in the range 2 to 10 mm at depth 0.5 to 1.7 mm in bakelite.

Comparisons with numerical modeling and the experimental results of the surface temperature contrast for different diameter and depth defects are presented. It has been found that full- width- at-half-maximum (FWHM) contrast provides an accurate indication of true defect size, in agreement with modeling predictions. For defect depth assessment, the approach is based on the slope of arising thermal contrast time dependence since the short time response at the defect centre is defect size independent.