Among the existing non-destructive testing techniques, the flying spot
photothermal technique [CITE] appears to be a good alternative to penetrant
testing for open-cracks detection in metallic structures. The technique
basically consists in the local heating of a structure under test and the
measurement of the temperature elevation which depends on the inspected
medium properties. During the scanning of the structure, thermal and optical
effects contribute to the elaboration of the photothermal signals. The
thermal effect is relative to the presence of a thermal barrier in the
inspected medium (e.g. crack) and the optical effects are due to the
variations of the absorptivity and diffusivity factors of the inspected
surface (surface conditions). Both effects are competitive and can lead to
hardly interpretable signals.
In this paper, the authors present a method allowing to separately identify
thermal and optical effects, in order to enhance the characterization of the
structure under test. The method was applied on a mockup featuring
open-cracks and rough surface conditions, and allows to construct separate
optical and thermal images. The resulting so-called thermal image allows to
significantly highlight the presence of the cracks. Besides, the optical
image enriches the characterization of the structure, since it supplements
the diagnosis of the cracks and also enables to characterize other defects
such as surface topology and features.