In this thesis project, a newly developed 3D laser vibrometer system was used to demonstrate that heating of the defect-free bulk correlates with local stresses in the material and is caused by damping of the ultrasound. Two additional mechanisms that lead to crack heating were identi ed as friction and plastic deformation. The measured quadratic relationship between heating and local displacements in the specimen is explained by an additional modulation of the normal force pressing the crack faces together. Due to the small displacements in the parts, it is necessary to postulate a mechanism strongly dominated by static rather than dynamic friction. Plastic deformation was only observed in extreme cases. Although local stress concentration occurs at crack tips, crack tip blunting as well as crack closure ordinarily prevent plastic deformation and crack growth. For the technical implementation, commonly used systems based on ultrasonic welding equipment were investigated and their disadvantages|especially with regard to reproducibility|were demonstrated and explained. Based on these results, a new technique was developed, which uses a tunable exciter to account for the individual eigenfrequencies of the specimen and to achieve resonant excitation of the specimen and to achieve a resonant excitation of the specimen. This also enabled increased eciency as a lower-power piezoelectric exciter is sucient to achieve the same displacements of the specimen./p> p>br /> Finally, necessary aspects for a technical implementation were investigated. Of particular interest are methods to characterize and verify the non-destructive nature of the procedure. Detection limits, post-processing methods for the infrared data, causes for false indications and a comparison with conventional NDT methods are also discussed./p>

English translation of the original German thesis "Untersuchungen zu Mechanismus und technischer Umsetzung der akustischen Thermographie" available here http://www.amazon.de/Untersuchungen-Mechanismus-Thermographie-Materialwissenschaft-Werkstofftechnik/dp/3832284958