Sizing the depth and width of ideal delaminations using modulated photothermal radiometry

Abstract

Delaminations, buried defects parallel to the sample surface, reduce the material stiffness and the structure reliability. Photothermal methods, based on exciting the surface by a light beam and analyzing the resulting temperature rise, have been extensively used for detecting delaminations and sizing their depth. However, less attention has been paid to the sizing of the delamination width. In this work, we use modulated photothermal radiometry (PTR) to size the depth and width of narrow delaminations by fitting the theoretical temperature expression to the experimental frequency spectrum of the PTR signal. We have established a detectability limit: for good thermal conductors, submicronic delaminations can be sized down to 10 mm, whereas for thermal insulators, it is difficult to go below 0.5 mm. Experiments on calibrated delaminations confirm these predictions.