Influence of hydrothermal ageing on the mechanical properties of an adhesively bonded joint with different adherends

Abstract The effect of hydrothermal ageing on the adhesively bonded joints of similar and dissimilar adherends, namely, aluminium alloy (AA7075) and glass fibre reinforced epoxy (GRE) was investigated. The practicality of the adhesively bonded joint technique was demonstrated using single lap joint (SLJ) configuration. The adhesively bonded SLJ specimens were hydrothermally aged in tap water. In order to estimate their long-term performance, an ageing process was performed on adhesively bonded joints at a constant water temperature of 50 °C with variable immersion periods (20, 40, 60, 80, 100, and 120 days). The mechanical strength of the joints was studied using tensile and fatigue testing with three combinations of materials, similar-AA7075/AA7075, similar-GRE/GRE, and dissimilar-AA7075/GRE, with the adhesive layer of two-part Araldite epoxy of 0.2-mm thickness. The tensile tests were performed at room temperature (RT) with a speed rate of 1 mm/min. The fatigue tests were performed at RT for the prolonged 120-days immersion SLJ specimens. Scanning electron microscopy (SEM) images were observed, and the relationship between the ageing period and strength of the adhesively bonded joint was determined. The comparison between unaged and aged specimens was discussed thoroughly. The results showed that as the exposure time increases, the moisture content of joint material increases. However, the joint strength decreases as the exposure time increases, which can be attributed to the effect of failure modes. Different types of failure modes were observed on the damage failure surface, namely, cohesive failure, adhesive failure, structural failure, and intralaminar failure.