Hygrothermal Aging of Structural Epoxy Adhesives Used in Wind Turbine Blade Composite Joints

Abstract

Two different epoxy adhesives that are widely used in wind turbine blades were studied. The aim was to investigate the adhesives moisture absorption and desorption behaviors and assess their mechanical performance degradation with the environmental exposure conditions. The cured adhesives were conditioned at 50 ºC and three different relative humidity levels of 43, 75, and 96% for 17 days, followed by vacuum drying at 40 °C for another 17 days. During moisture absorption and desorption tests, periodic gravimetric measurements were conducted to obtain moisture saturation concentrations, diffusion coefficients, and residual moisture concentrations. The results revealed that the moisture saturation concentration increased 3-4 folds as the RH level was changed from 43 to 96%, while the diffusion coefficient was decreased. The permanent damage related to the environmental conditioning was then measured by tensile testing of fully conditioned samples. A significant drop in both the modulus of elasticity and the strength as well as a mild decrease in the strain at break were observed for both adhesive systems.