Innovative lockin interferometry (providing phase images which display the local delay between heat injection and local bending) differs substantially from conventional vibration interferometry where mechanical resonances are being used whereas in this paper the bending frequencies are so low that a mechanical wave would have about the same phase all over the sample. Phase angle effects are therefore related to thermal wave effects where wavelengths in the mm...cm range are involved. So lockin interferometry is like lockin thermography based on thermal wave interaction with hidden features, it is just a different way of analysing them, but it is as well a remote technique with the option of depth profiling via modulation frequency with the extra advantage of an enhanced depth range. These features make the new technique well suited for non-destructive testing of aerospace structures, as has been shown above for several examples where typical defects (resin in honeycomb structure, quality of repair, impact, delamination) could be found in CFRP components with a substantially higher signal to noise ratio and hence a better probability of detection (POD) than with conventional shearography or ESPI-techniques.
Lockin interferometry. Principle and aerospace applications
Lock-in-Interferometrie. Prinzipien und Raumfahrtanwendungen
2008
8 Seiten, 10 Bilder, 15 Quellen
Aufsatz (Konferenz)
Englisch
Lockin Interferometry: Principle and Aerospace Applications
TIBKAT | 2008
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