Prüfung von Klebverbindungen mit Thermographie und thermischen Wellen

Nondestructive testing by means of thermal methods is based on detection of different thermophysical material properties. Defects in bonded structures are a barrier to thermal diffusion. Thus, these defects are detectable with thermal methods. The testing object is heated by a heat pulse or periodically at its surface. Near-surface defects lead to a contrast in temperature at the surface or in very thin specimens on the back side during the diffusion of heat into the material. By measuring the response time with the pulsed technique, as well as the signal phase according to the excitation, caused by the periodical heating, information about the defect depth can be obtained. For fast testing of large objects, infrared cameras are used. By applying scan techniques in combination with a heating of the specimen with a laser, high-resolution (microscopic) images of the specimen can be obtained. This method, e.g., can be applied for microsystems. The analysis of the response time or the phase signal provides the possibility to determine the thickness of lacquer coatings. As this is a contactless technique, it is also possible to test lacquers which are not yet completely cured. The various testing possibilities by means of pulsed and lock-in techniques are demonstrated with examples