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Impulse-thermography has been established as a fast and reliable tool in many areas of non-destructive testing. In recent years several investigations have been done to apply active thermography to civil engineering. For quantitative investigations in this area of application, finite difference calculations have been performed for systematic studies on the influence of environmental conditions, heating power and time, defect depth and size and thermal properties of the bulk material (concrete). The comparison of simulated and experimental data enables the quantitative analysis of defects.
Abstract
In the recent years the application of infrared thermography and especially its active approaches lock-in thermography, impulse themography and pulse phase thermography (PPT) has gained more importance for non-destructive testing (NDT). In this paper it is demonstrated that PPT is very well suited for NDT in civil engineering. The method is based on pulse heating of the investigated specimen and on the observation of the cooling down process on its surface with an infrared camera. The transient behaviour is afterwards analysed with Fast Fourier Transformation, enabling the creation of phase and amplitude images with enhanced visualisation of the defects. Results of European and National (i.e. DFG) funded projects are presented, for example the detection of voids and inhomogeneities close to the surface and the localisation of delaminations on plastered concrete and masonry specimen.
ZUSAMMENFASSUNG
Im Rahmen eines von der Deutschen Forschungsgemeinschaft geförderten Vorhabens zur zerstörungsfreien Prüfung im Bauwesen wird in der Bundesanstalt für Materialforschung und -prüfung (BAM) in Zusammenarbeit mit der Technischen Universität Berlin (TUB) die Puls-Phasen-Thermografie (PPT) weiterentwickelt, bewertet und eingesetzt. Die durch die Impuls-Thermografie (IT) aufgenommenen Daten werden mittels Fast Fourier Transformation (FFT) bearbeitet. Die durch die FFT gewonnenen Phasenbilder reduzieren die Störeinflüsse von Oberflächeninhomogenitäten und ungleichmäßiger Erwärmung.
Die dargestellten Ergebnisse zeigen deutlich, dass sich die PPT sehr gut zur zerstörungsfreien Prüfung im Bauwesen eignet. Insbesondere Inhomogenitäten im oberflächennahen Bereich, wie Ablösungen und Hohlstellen hinter Beschichtungen (Putz, CFK-Laminate etc.), aber auch Defekte in größeren Tiefen können zuverlässig geortet und bildgebend dargestellt werden.
Struktur- und Feuchteuntersuchungen von Bauteil- und Bauwerksoberflächen mit der Impuls-Thermografie
(2005)
An advanced quantitative approach of pulse-phase-thermography for nondestructive
testing in civil engineering is described in this contribution. The
characteristic frequency of the maximum phase-contrast between defects and sound
areas is used as a means for the characterization of its depth.
The new approach is tested in the laboratory on concrete structures with defects of
polystyrene. The surfaces of the structures were heated with IR-radiators for varying
time periods.
The presented investigations were funded by the Deutsche Forschungsgemeinschaft
(DFG) and were carried out in co-operation with the Technical University of Berlin
(TUB).