Three-dimensional detection of buried defects using infrared flash thermography: analytical framework, simulation and experimental validation

Buried defects occur below the surface of an object. Their thermal properties can lead to changes in the temperature of the surface due to non-symmetrical diffusion through the material. It is possible to detect these defects from the variation of the surface temperature even though they are buried deep inside material. In doing so, the relationship of the contrast obtained at the surface due to buried defects must be linked to the shape and the location of the defect. Initially, we tackle this by reducing a region of interest in three-dimension (3D) to a two dimensions (2D) problem with respect to peak contrast time, or positions from the surface. Both simulation and experimental thermograms were used to determine their detectability in 3D. We used known materials of known shape at known distances beneath the surface. We will start with a theoretical 2D assessment of the problem, as well as 2D simulations, operating as a cross sectioning of the 3D problem. This is a suitable simplification when considering heating along one axis, yet still leads us to a 3D-Infrared Thermography methodology using angled excitation that enables observe changes in surface temperature due to geometry and location of buried defects.