Effect of cyclic aging on mode I fracture energy of dissimilar metal/composite DCB adhesive joints

In some industrial applications, adhesive joints are cyclically exposed to a moist environment, where cyclic moisture absorption and desorption can significantly alter the fracture energy of the bonded joints. Most previous studies are based on monotonic aging conditions, while the performance of bonded joints under cyclic aging is not well explored The aim of the current study is to investigate the effect of cyclic aging on mode I fracture energy of dissimilar DCB (double cantilever beam) adhesive joints. Accordingly, bulk adhesive plates were manufactured and exposed to 4 aging cycles. After the aging process, at different exposure times, the aged adhesive plates were used to bond dissimilar Al/GFRP substrates using a secondary adhesive. Then the prepared DCBs were tested and subsequently the mode I fracture energy of the adhesive was determined. Meanwhile, using gravimetrical tests and numerical simulation, moisture diffusion of the adhesive layer in different exposure times was analysed. Using experimental and numerical results, the variation of fracture energy as a function of moisture uptake was studied. In addition, glass transition temperature (Tg) and chemical bonding of the aged adhesive were analysed in different aging cycles. The results showed that by increasing the number of aging cycles, the reduction rate of mode I fracture energy between the aging cycles decreases.