ADHESIVE JOINT DURABILITY ASSESSED USING OPEN-FACED PEEL SPECIMENS

This paper presents an investigation of the durability of two aluminum -epoxy adhesive systems by means of open-faced peel specimens. A peel analysis model was used to determine the fracture energy from the peel data. Both wet and dry peel tests were conducted in order to distingu ish between the reversible and the permanent effects of water. The eff ects of water on the cohesive properties of the adhesives were also as sessed by tension tests. It was found that, for the two-part epoxy adh esive, which plasticized to a large extent, the Feel testing should be carried out in a dry state to assess the interfacial weakening. It wa s also observed that the two-part adhesive was much stiffer in the dry , degraded state, and it was important to take account of such permane nt changes in the cohesive properties associated with water uptake whe n determining the fracture energy from the peel data. In contrast, the one-part epoxy system did not suffer from appreciable cohesive change s, either reversible or permanent. In this case, both wet and dry fail ure loci were interfacial, and some of the interfacial damage was foun d to be reversible. Finally, surface analyses of the peel failure surf aces were carried out, and the formation of micro-debonds was identifi ed as a possible mechanism of degradation for the two-part system.