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- Active thermography (3)
- CFK (3)
- Aktive Thermografie (2)
- B. Delamination (1)
- B. Thermal properties (1)
- Blitzanregung (1)
- Blitzthermografie (1)
- CFRP (1)
- CFRP reference (1)
- D. Non-destructive testing (1)
Eingeladener Vortrag
- nein (2)
Standards for the application of flash thermography as well as of lock-in thermography are urgently required.
Both methods are applied more and more often in research and industry, but still extensive validation procedures are required for each individual application. In this paper, the results of two research projects concerning the validation and standardisation of both methods are presented. This includes results of a detailed study of the influence of measurements parameters on flash thermography, of the comparison of the lateral resolution obtained with flash and lock-in thermography and the description of a draft standard for flash thermography.
Carbon fiber reinforced polymer (CFRP) specimens with artificial delaminations and with impact damage have been characterized using active thermography with flash excitation. Systematic investigations have been performed in four different experimental configurations of flash lamps and infrared (IR) camera in transmission as well as in reflection alignment. It is shown here that the diffusivities determined for the sound and for the damaged areas give a good measure for damage characterization. Although reflection measurements also give information about defect depth, reflection measurements from only one side are not sufficient for assessing the whole cross section of the specimens. Thus, depending on sample thickness the lateral size of damage could only be determined from reflections measurements from both sides or from transmission measurements. In this paper, measurement accuracy and limits of flash thermography for the investigation of CFRP specimens are presented in detail together with quantitative data concerning the defects.
Anwendungsbreiche und Grenzen der Blitzthermografie - Entwicklung eines anwendungsnahen Standards
(2012)
In this contribution, the authors present the results of a project which involves the
development of a testing standard for flash thermography. In addition to the standardization of
the selection of appropriate equipment and procedures for testing and data analysis, the new
standard will provide suitable reference test specimens for several materials, including CFRP
as used in aerospace applications with typical flaws. We will particularly consider these test
specimens which should enable qualification of the equipment as well as the validation of the
flash thermography method for CFRP in general.
With increasing use of carbon fibre reinforced polymers (CFRP) in civil aviation, the need for nondestructive testing (NDT) techniques has gained significance. One of the very promising methods is active thermography with flashlight excitation (flash thermography). Already exploited to detect faults in CFRP laminates it is yet not recognized as test method for the very reason an international user standard is missing. The authors will present the results of a project involving the development of a testing standard for flash thermography. In addition to the standardization of the selection of appropriate equipment and procedures for testing and data analysis, the new standard will provide suitable reference test specimens for several materials, including CFRP. These test specimens should enable qualification of the equipment as well as the validation of flash thermography. For this purpose, specimens of CFRP prepregs containing various typical flaws have been manufactured. These flaws are similar to those which occur in operation, for example as a result of an impact. The impact specimens have been constructed and damaged according to DIN 65561 with energies ranging from 4 to 24 J. Other specimens contain flaws similar to those which are caused by production processes, for example deviating fiber direction. Systematic measurements and new methods of analysis enhanced the knowledge about best experimental set ups for detecting different flaws. Furthermore the accuracy of the defect size examination with flash thermography had to be judged. For this purpose specimens with well known artificial defects have been investigated. These specimens have been performed as stepbars with inclusions of double layered Polytetrafluorethylen (PTFE) foil platelets in squares sized from 2 to 20 mm². The steps ensure laminate coverings of the defects from 0.5 to 5.5 mm². In combination with new developed data analysis, the measurements on the stepbars demonstrate that this type of specimens might conceivable for adjustment of flash thermography set ups and should be recommended for the future standard. Some of the experimental findings are still debated and further research is needed in order to establish a well prepared user standard for flash thermography. Since the project will end at the beginning of 2013 these questions will be explored, whereby the transferring of conclusions to on-site applications is of particular interest.
Untersuchung der Auflösungsgrenzen der Lockin-Thermografie zur Prüfung von Faserverbundwerkstoffen
(2014)
Aktive Thermografie mit Lockin-Anregung stellt ein berührungsfreies und zerstörungsfreies Prüfverfahren dar, welches 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.
Dabei wurden unter anderem der Einfluss der spektralen Empfindlichkeit verschiedener Kamerasysteme, unterschiedlicher Lagenaufbauten bei CFK-Probekörpern und der Einfluss einer Phasenverschiebung zwischen dem Anregungssignal und der Detektion der Thermografiebilder untersucht.
Standardisierung der Lockin-Thermografie: Vorstellung des TNS-Projektes und Auswahl der Probekörper
(2013)
Ziel des Verbundprojektes zwischen der BAM und dem IKT der Universität Stuttgart ist die Festlegung einer einheitlichen Vorgehensweise für die Auswahl der Gerätekomponenten und für die Durchführung von Prüfungen mit der Lockin-Thermografie. Daraus soll ein Standard abgeleitet werden, der die Prüfung
unterschiedlicher Materialsysteme auf Fehlstellen mittels Lockin-Thermografie unter Berücksichtigung verschiedener Anregungsquellen ermöglicht. In diesem Beitrag wird die Entwicklung der Probekörper vorgestellt, die in diesem Projekt untersucht und später als Referenzprobekörper verwendet werden können.