Thermography is a contactless and imaging procedure to detect hidden component defects (e.g. inclusions, voids or delaminations). It is based on the method of detecting defects in the volume of a component that result from the changing surface temperature. Thermography is particularly well known in medical technology, in construction and in electrical engineering. It is also used to detect external and near-surface defects in thin-walled fiber-reinforced composites, as found, for example, in aerospace and in automotive industry. Basically, a distinction is made between passive and active thermography, depending on whether a self-heating of the component (e.g. by friction), cooling after a manufacturing process or an external heat source for heating the surface are used. There are numerous implementation methods and measurement evaluations to increase the sensitivity, such as pulse-phase thermography, thermographic signal reconstruction, pricipal component thermography and lock-in thermography.
These methods are based on an active thermal excitation of the surface and a resulting heat flow inside the object, whereby the heat flow is disturbed by internal defects and bound- aries which leads to a change of the surface temperature, and a subsequent evaluation of the time-dependent change of the surface temperature. This enables component control within the scope of inspection and maintenance or a quality control following production and joining processes. IVW uses this method in a variety of ways in different projects, e. g. in the frame of EU-funded project “FlexHyJoin” for the automated joints inspection of hybrid components made of a thermoplastic and a metallic joining partner. In addition, the method is used during the material characterization, in quasi-static tensile tests of multi-axial high-performance composites, for example. The progress description of near-surface damage events, which release energy in the form of heat during their formation, can be observed online during the experiment.