Thermo-oxidative and hydrothermal ageing of epoxy-dicyandiamide adhesive in bonded stainless steel joints

Abstract

The ageing behaviour of stainless steel joints bonded with hot-curing adhesives is crucial for their reliability and durability in engineering applications. In industry, accelerated artificial ageing regimes are combined with short-term mechanical tests to simulate the in-service long-term behaviour and to predict the life time of the adhesive joints. With such a focus on mechanical bond strength, chemical changes in the adhesive are widely disregarded. Hence, neither the very causes for the decreasing performance of the joint nor their relevance for application can be revealed. Reasoning this study, lap shear samples of the stainless steel alloy 1.4376 are bonded with an epoxy-dicyandiamide adhesive and aged artificially under moderate thermo-oxidative (60 °C, dried air) or hydrothermal (60 °C, distilled water) condition. After testing (shear stress-strain analysis), chemical modifications of this adhesive due to ageing are detected on the fracture faces by μ-ATR-FTIR-spectroscopy as function of ageing time and position in the adhesive joint. The results attest high thermo-oxidative stability to these adhesive joints. For hydrothermal ageing, permeating water deteriorates the EP network from the edges towards the centre of the joint via hydrolysis of imine groups to ammonia, amine species and carbonyls. © 2009 IOP Publishing Ltd.