The Dimensional Stability of Epoxy Adhesive Joints

Abstract

An interferometric technique which employs Moiré patterns has been used to study the deformation that occurs when an adhesive joint undergoes water uptake. It has been demonstrated that very large swelling stresses can be generated as a result of the inhomogeneous swelling. The magnitude and position of these stresses can be obtained by application of equations developed from beam and elasticity theory. A consequence of this analysis is the prediction of damped normal displacement waves in the cover slip in regions of negligible water concentration. This is observed experimentally. Measurements are reported on the irreversibility of dimensional changes when an adhesive joint is subjected to uptake and subsequent removal of the water responsible for swelling — on the assumption that the epoxy based adhesive is free from shear stresses during the cure — and on the influence of dissolved inorganic salts upon the swelling behaviour.