The strength of bonded carbon fibre composite joints exposed to high humidity

Abstract Carbon fibre reinforced epoxy composite joints bonded with epoxy adhesives were exposed to 50°C/96% RH for up to 3 years. Strength reductions were measured which depended on both exposure time and test temperature. Adhesives cured at 175°C gave better retention than those cured at 120°C. Strength changes were dependent on changes in the adhesives rather than in the composite adherends. There was no evidence of disbonds between adhesive and composite developing as a result to exposure: after failure of the adhesive through the fillet, the crack propagated in the adhesive, or in the composite, or both, depending on the adhesive.