Effect of Water and Mechanical Stress on Durability

Abstract

Adhesive joints with structural adhesives are weakened significantly in air at high humidity, and the rate of decline is controlled by water diffusion into the adhesive. There appears, however, to be a critical relative humidity, and only if this is exceeded are joints significantly weakened; evidence is that this is about 65%. The most harmful effect of water is potentially at the interface between the adhesive and adherend; however, surface treatment of metallic adherends can greatly improve water durability. Accelerated aging using elevated temperatures and humidities can provide information on the environmental resistance of different systems but does not easily correlate to aging in natural conditions. The entry of water into the adhesive layer can conform to the simple Fickian model, which just depends on two parameters (diffusion coefficient and solubility coefficient), but in some cases it is non-Fickian. Current state-of-the-art