In this paper, a new absolute thermal contrast method is proposed for pulsed infrared thermography. It is based on the computations of reconstructed defect-free images so that no a priori knowledge of a sound area on the sample is necessary. Moreover, a correction is applied to take into account possible delays in the acquisition time. Results are presented both on Plexiglas TM and graphite-epoxy specimens. Comparisons with Pulsed Phase Thermography phase images are also presented along with a discussion on the advantages of the proposed method.

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Lockin thermography with its capability to monitor modulated heat flow in larger areas (several m 2 ) within a few minutes is applied to the inspection of aircraft. Using up to 6 lamps each with a power of 1 kW, we could inspect subsurface structures (e.g. stringers) and subsurface defects (e.g. impact, delaminations) from a distance of several meters. The method is well suited to monitor the structural integrity of aging aircraft in the near-surface area. By using ultrasonic excitation instead of radiation one can display selectively hidden defects that are characterised by a local enhancement of mechanical loss angle (e.g. cracks).

A succinct depth analysis of Pulsed Phase Thermography (PPT) is presented in this paper. Some theory is presented as well including some comparisons with modulated (or lockin) thermography (MT).

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