A Possible In-Situ Thermal History Indicator for Uncured Film Ad hesives

A range of epoxy formulations, typical of aerospace adhesives, containing a pyrazolone dye, has been shown to undergo a reaction which results in a change in colour of the formulation. The rate of reaction depends greatly on the particular epoxy resin. The extent of reaction may be determined by direct coiour measurement or by chromatographic analysis of the remaining dye level. The possible use of this reaction as an in-situ thermal history indicator is discussed.     

Strength of adhesive joints with adherend yielding: II. Peel experiments and failure criteria

Peel tests were conducted with an epoxy adhesive on nine rigid-flexible peel configurations: combinations of 1, 2, and 3 mm aluminum adherend thickness and 30°, 60°, and 90° peel angle. The peel model described in an accompanying paper was used to calculate the stress and strain distributions in the adhesive, the strain energy release rates, and the root curvature of the adherend corresponding to steady-state peel failure. Two failure criteria were examined: the critical von Mises strain and the critical fracture energy, G c . The first criterion was found to be essentially independent of the peel angle but dependent on the thickness of the peel adherend. It produced predictions of the peel force that had an average error of 11%. The fracture energy criterion showed that G c depended on the average phase angle of the loading. This criterion was preferred, having an average prediction error of 6% over the nine experimental cases, and requiring fewer free parameters.