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Quantification of damage processes at surfaces and interfaces of building structures using optical methods and active thermography

Quantifizierung von Schadensprozessen an Oberflächen und Grenzflächen von Gebäudestrukturen mittels optischer Verfahren und aktiver Thermographie

European Federation for Non-Destructive Testing -EFNDT-:
10th European Conference on Non-Destructive Testing, ECNDT 2010. CD-ROM : 7.-11.06.2010, Moskau
Moskau, 2010
10 pp.
European Conference on Non-Destructive Testing (ECNDT) <10, 2010, Moskau>
Conference Paper
Fraunhofer IFF ()

In this presentation, the specifications, advantages and limits of both methods will be presented. With the light section method, a very precise determination of position is possible. Arbitrary surfaces can be surveyed with an accuracy of about 0.1 mm. 2D photos can be concatenated. The disadvantages are the complexity of the experimental set-up as well as the data analysis. Latter will be further developed in the presented work. With active thermography, inhomogeneities below the surface can be detected up to a depth of about 10 cm. A maximum spatial resolution of 0.3 mm is possible, but can be enhanced by using a close-up lens. For recording of congruent mappings of the object under investigation, first the internal aberrations of the IR cameras have been corrected (internal camera calibration) by using a freeware matlab toolbox. This calibration reveals, that uncorrected thermograms show considerable distortions up to 5 % at the boundaries, which cannot be neglected for datafusion. For facilitating the fusion to the 3D data, parallel to the capturing of thermograms digital photos are taken from the measurement object. For this, IR camera and digital camera were both mounted into a common frame structure enabling a reproducible relative position. Both methods have been applied to several historic buildings, compiling experimental data that will be presented in the following. Investigations of a sculpture (Madonna with child in the dome of Halberstadt) and of a sandstone column (dome of Magdeburg) are presented. With the help of the introduced approach and the developed software the thermograms can be visualized and analyzed three-dimensional for any complex object geometry. The combination of infrared images of unsteady thermal heat transfer processes with geometric 3D data enables the discrimination between external geometrical effects due to material properties and internal faults. Temporal changes can be observed with the demanded high local accuracy and damage can be recognized on time.