Optically excited lockin thermography (OLT) is based on propagation and reflection of thermal waves which are launched from the surface into the inspected component by absorption of modulated radiation. Phase angle images obtained by superposition of the initial thermal wave and its internal reflection display hidden thermal structures down to a certain depth below the surface. Defects are found by comparing the observed features with expected features provided by theory or by an intact reference sample. Phase Thermography (Lock-in or Burst) has some advantages as compared to conventional pulse thermography: sensitivity variations within the detector array as well as optical sample characteristics are suppressed. Furthermore the signal to noise ratio is improved significantly. Compared to OLT, using the ULT / UBP methods in CFRP defects can be detected up to a depth of 12 mm. Using UBP the probability of defect identification is thus improved at a reduced measuring time. The measurements presented in this paper show that even larger components can be examined with this technique. However, the high excitation power contained in short pulses or bursts could possibly cause damage of the inspected structure. Standing waves can occur if the frequency applied to the sample is at a mechanical resonance. Due to hysteretic losses in the elongation maximum, these standing elastic waves can appear as temperature patterns. which can cause misinterpretations. To eliminate standing wave patterns and to reduce the high excitation power the application of small piezo-ceramic actuators was investigated. Good results where found for relatively small samples. However, the must be improved to make this technique applicable to non-destructive testing of large structures.


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    Titel :

    Lockin thermography methods for the NDT of CFRP aircraft components


    Weitere Titelangaben:

    Lockin-Thermographieverfahren zur ZfP von kohlefaserverstärkten Kunststoff-Luftfahrtkomponenten


    Beteiligte:
    Zweschper, T. (Autor:in) / Dillenz, A. (Autor:in) / Riegert, G. (Autor:in) / Scherling, D. (Autor:in) / Busse, G. (Autor:in)


    Erscheinungsdatum :

    2002


    Format / Umfang :

    9 Seiten, 9 Bilder, 24 Quellen


    Medientyp :

    Aufsatz (Konferenz)


    Format :

    Datenträger


    Sprache :

    Englisch




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