Simple model to estimate adhesion of structural bonding during humid ageing

A structural epoxy adhesive has been studied under humid ageing conditions, both as a bulk polymer and as an adhesive, in torsional and cleavage (wedge) tests. Diffusion of water within the polymer, as measured by gravimetry, was found to be in good agreement with the Carter and Kibler model. Physical properties decreased with increasing water content. A correlation was found between the decrease of bulk and adhesive joint properties. Fracture surfaces have also been explained using the Carter and Kibler model. Given the various types of failure, the extent of each depending on time of immersion, a simple model is proposed to estimate overall energy of adhesion, G* (an effective average linked to three distinct types of failure), as a function of ageing time.