Nondestructive evaluation of plexiglas materials using lock-in and pulse phase infrared thermography

Lock-in and pulse phase infrared thermography measurement techniques have been exploited for quantitative assessment of subsurface defects in a reference specimen made of Plexiglas. Radiometric thermal images were post-processed using a contrast approach in the frequency domain, allowing defect depth location to be resolved with a relative combined standard uncertainty of about 7% for thicknesses above 3 mm. Conversely, significant radial heat diffusion next to the boundary of the discontinuity made accurate sizing of deeper subsurface defects more difficult. The obtained results demonstrate the potentiality of active thermography as a fast, powerful contactless NDT measurement tool.