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- CFK (1)
- CFRP (1)
- Defect shape reconstruction (1)
- Echo defect shape (1)
- Faserkunststoffverbunde (1)
- Fibre-reinforced plastics (1)
- Impulse-thermography (1)
- Inversion (1)
- Levenberg-Marquardt method (1)
- Lock-in Thermografie (1)
Active thermography with lock-in excitation is a non-destructive testing method that is also feasible for testing of carbon fiber reinforced polymers (CFRP). For validating the method extensive investigations were done during a research project in order to advance a standardization process.
The most important parameters of optical and ultrasonic excitation thermography were investigated. For example, the appropriate selection of spectral sensitivity of the used infrared camera systems is important for recording undisturbed thermal signals. Regarding excitation,
influences of excitation power and ultrasonic frequency were studied. Furthermore, material parameters such as CFRP layup are known for strongly affecting the results of
measurement.
Aktive Thermografie mit Lockin-Anregung ist ein zerstörungsfreies Prüfverfahren, das insbesondere auch die Prüfung von kohlenstofffaserverstärkten Kunststoffen ermöglicht. Um eine Standardisierung dieses Verfahrens voranzubringen, wurden im Rahmen eines Forschungsprojektes umfangreiche Untersuchungen zur Validierung des Verfahrens durchgeführt. Für die Anregungsmethoden optisch und Ultraschall wurden die wichtigsten Parameter systematisch untersucht. Auf der Auswertungsseite ist dies z.B. der Einfluss der spektralen Empfindlichkeit verschiedener Kamerasysteme. Für die Anregungen sind unter anderem die Einflüsse von Anregungsenergie und Ultraschallfrequenz untersucht worden. Auch Materialparameter, wie der Lagenaufbau bei CFK-Probekörpern, beeinflussen die Ergebnisse stark.
The paper presents numerical methods to detect and classify defects and inhomogeneities by means of active thermography. The objective is to determine the wall thickness of structure elements with an inaccessible back wall, for example, of pipes or Containers. As test specimens we used approximately 2 cm thick PVC samples with spatial variations in the back wall geometry. Flash lamps provided the heating. To know the thickness of the wall, we used two inversion methods and compared the results achieved. One is an iterative echo defect shape method and already tested on Steel test specimens with good reconstruction results. The second one is the Levenberg-Marquardt method, applied here to thermographic data for non-destructive testing. Since data capturing using active thermography and the presented numerical methods can easily be automated, the combination of these two procedures is a promising approach providing a broad area of application.