Abstract Structural adhesives are increasingly being used in the aerospace and automotive industries. They allow for light weight vehicles, fuel savings and reduced emissions. However, the environmental degradation of adhesive joints is a major setback in its wide implementation. Moisture degradation of adhesive joints includes plasticization, attacking of the interface, swelling of the adhesive and consequent creation of residual stresses. This may lead to reversible and irreversible damage. In this work double cantilever beam (DCB) specimens using two different adhesives for the automotive industry were subjected to two different ageing environments. They were tested periodically until the toughness of the adhesives stabilized, which means that they were fully degraded. An association was made between the toughness of the adhesive and the amount of water that it had absorbed. This way it was possible to indirectly measure the water uptake in an adhesive joint taking into account the water uptake properties of the adhesives studied, which had been determined in another study. It was found that diffusion of water into the studied adhesive joints was faster than diffusion through the bulk adhesive alone. A model that takes into account diffusion through the interface between the adhesive and the adherends was proposed.

Abstract Surface treatment of the adherends prior to adhesive bonding plays an important role in the enhancing of strength and durability of bonded joints. In this work, an investigation on effect of adherend surface roughness on adhesive bond strength was performed. Single strap joints with different adherends (mild steel and aluminium) bonded with an epoxy resin (Araldite(r) 2015) were tested. The adherend surface was treated by mechanical abrasion process using an emery paper. Contact angle measurement and SEM analysis to understand the wettability and the failure mechanism of the joints were performed. It was found that an optimum surface roughness exists for a maximum bonding strength and the roughness range depends on the adherend material. The joint strength changes are associated not only simply by the increased bonding area, surface texture or mechanical interlocking, but also by the chemical characteristics of the surface and the chemical bond between them.