Automated adhesive seam inspection with lockin thermography
Inline testing with optically excited lockin thermography
The testing of adhesive joints may be required with regard to strength or heat transfer. Active thermography helps to check even complex adhesive joints and to determine the adhesive distribution, for example.
For composite structures, it’s all about laminate integrity, i.e. detection of ply structure, prevention of delamination within the laminate, detection of dry spots or resin build-up, inspection of coatings, and much more…
A test takes between a few seconds and several minutes, depending on the material and thickness. Ideally, the test takes place stationary, but can also be carried out in continuous motion if necessary.
Principle of optically excited lockin thermography
The optical lockin thermography (OLT) method is based on heat flow analysis.
The surface of the object under investigation is heated with halogen lamps. The resulting heat flow into the material is altered by thermal obstacles such as impacts, delaminations or material thickness variations of the object. As a result, thermal signatures form on the surface, which are captured by an infrared camera. The sensitivity of the method is very high due to the use of the lockin technique. The intensity of the halogen lamps is modulated sinusoidally and the surface temperature is recorded at the same time. A phase and amplitude image is calculated from the measured image sequence by means of a Fourier transformation. In the phase image, interference effects resulting from different emission coefficients or inhomogeneous excitation are significantly reduced. The statement about the interface state and/or the material thickness or the coating thickness is now possible.