Three-dimensional infrared thermography of buried defects from multi angle long pulse thermography

Heat diffusing from the bulk of an object manifests at the surface of an object due to variations in structure and materials, which can give rise to thermal property variations. This allows for detection of defects, their size, shape, and location within an object. As such, Infrared Thermography (IRT) finds its applications in aerospace industry, additive manufacturing, welding and carbon fibre composites and medical diagnostics. Combining IRT ability to visualize internal defects with imaging and heating an object from multiple angles, a three-dimensional (3D) reconstruction can be achieved to provide 3D-IR thermography (3D-IRT).

The approach outlined here intends to construct the 3D geometry of a defect from a set of 2D surface images. Time domains and pulsed regimes have also been explored in 3D thermography [36-38]. These methods though have shortcomings in edge resolving, resolution and material of use. In this thesis, we demonstrate a relatively simple approach, with the addition of tilting the heat source we can capture thermal images contrast of buried sections from which heat diffuses out to the surface. This differs from conventional thermal-tomography as the camera itself is maintained at a constant angle and the excitation angle is varied. Due to the illumination of the defect originating from the flash heating, the heat sources angle allows for highlighting features of the defect otherwise impossible to visualize with symmetric heating of the defect.

This work looks to semi quantitatively present the detectability of defects z-direction information from non-symmetric angled excitation.