Effects of ageing frequency on the interfacial failure and tensile properties of adhesively bonded Arcan joints exposed to cyclic ageing environments

The strength and durability of adhesive joints are significantly influenced by environmental conditions. When working in a humid environment, the adhesive tends to absorb moisture and this phenomenon can drastically reduce the mechanical performance of the adhesive joints. In practise, joints are usually subjected to cyclic ageing due to moisture absorption and desorption. Accordingly, it is necessary to study the ageing behaviour of the adhesives when they are exposed to environments with cyclic humidity conditions. Accordingly, the current study investigates the mechanical properties of adhesive joints with an epoxy-based adhesive subjected to cyclic ageing conditions using Arcan joint specimens. To this aim, static tensile tests were performed for both cyclic aged, dried, and unaged Arcan joints. The effect of cyclic ageing and drying conditions, such as absorption and desorption mechanisms, on the mechanical properties of the joints were studied. In the numerical part, an experimentally obtained diffusion coefficient (D) was used to simulate the water diffusion in Arcan joint. The results showed that key mechanical properties, such as tensile strength and displacement of the joints are reduced by the number of ageing cycles. The maximum strength degradation of the aged joints compared to the unaged condition was 94% for the third ageing cycle. For the dried condition, the strength of the joints was recovered although it was not fully returned to the initial stage. It was also found that the recovery ratio increases with the ageing cycles. It is shown that a short drying process can significantly recover the mechanical response of the cyclically aged adhesive joints, especially at higher ageing cycles.