Failure of epoxies bonded assemblies: comparison of thermal and humid ageing

This paper deals with the effect of Ti/epoxy/Ti bonded assemblies submitted either to wet (70 degrees C, 85% HR) or thermal (120 degrees C in oven) ageing. It was observed that humid ageing leads to an adhesive failure whereas thermal ageing leads to a cohesive one with the appearance of cracks at the edges of samples. The mechanical failures were shown to be mainly driven by the degradation of the epoxy adhesive. The thermal and water ageing of epoxy was thus studied and some relevant parameters (water diffusion coefficient for humid ageing, oxidation rate and thickness of oxidized layer for thermal ageing) were estimated so as to discuss on the predominance of thermal or humid ageing depending to the exposure conditions.