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Laser-acoustic, thermal and mechanical methods for investigations of bond lines

: Jansen, I.; Schneider, D.; Häßler, R.


International journal of adhesion and adhesives 29 (2009), Nr.2, S.210-216
ISSN: 0143-7496
ISSN: 1879-0127
Fraunhofer IWS ()
Klebverbindung; Aluminium; Epoxidharz; Adhäsion; Haftfestigkeit; Zwischenphase; photoakustische Spektrometrie; Schichtstruktur

The curing of epoxy adhesives on metal adherends produces interphases near the substrate surface. The detn. of the interphase thickness in small joints will be complicated due to the influence of the adherend. To exclude this effect from the characterization of the interphase, resin-metal-composites were created by spin-coating process of different resin layer thicknesses on the aluminum surface. Before the tests, the coated aluminum was cured. The thickness of the cross-linked epoxy layer ranges between 2 and 150 micro m. These coated sheet metals were characterized by a new laser-acoustic method (LAwave) and by micro-thermal anal. (micro TA). Both methods are non-destructive. LAwave is based on the measurement of laser-induced surface waves. It enables the Young's modulus of thin films to be detd. The micro TA was used for studying the interphase formed composites based on aluminum and epoxy resin. It is a thermo-anal. technique that combines the principles of scanning probe microscopy with thermal anal. This allows samples to be spatially scanned in terms of both topog. and thermal cond. It is possible to perform localized thermal anal. expts. on discrete small regions with high resoln. The results were compared with results of mech. (nanoindentation) investigations. We could detect an interphase of some micrometers (about 25 micro m) between the aluminum surface and the epoxy-bulk phase.