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When a composite laminate is subjected to humidity, moisture diffusion occurs depending on the number and thickness of the lamina. Water diffusion changes the mechanical response of laminates and usually causes a significant reduction of the mechanical properties of the composite specimens in ocean structures. One of the most important mechanical properties of laminates is flexural stiffness which should be considered in the design procedure. Despite the extensive research on single cycle aging of composites, cyclic aging of these materials is less explored. The aim of the current research is to investigate the variation of mechanical properties of carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP) composites as a substrate in adhesive joints with the same initial flexural stiffness values subjected to cyclic wet/dry aging conditions for long-term structural applications. The matrix used in the CFRP and GFRP composites are based on epoxy and vinyl ester, respectively. Both unaged and cyclically aged samples were characterized by tensile and three-point bending tests. In order to simulate the moisture absorption condition of composites in adhesive joints, one side of the composite laminates was sealed with aluminum foils and three sides were exposed to humidity. The interaction between the composite thickness and the number of aging cycles was also investigated. The experimental results show that in cyclic aging condition, the reduction of flexural stiffness in CFRP is more than GFRP laminates and GFRP laminates is more suitable for ocean applications., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public, Structural Integrity & Composites

Adhesive joints are frequently exposed to cyclic ageing conditions during their service life, which can have a substantial impact on the mechanical properties of both the adhesive and the substrates. The safe life philosophy, commonly employed in the design of bonded joints, underscores the importance of obtaining an accurate estimate of the adhesive's durability. Therefore, it is essential to enhance the predictive capabilities of the adhesive's mechanical behavior under cyclic ageing conditions. This research aims to expand the use of quasi-static cohesive zone modelling (CZM) for damage and fracture analysis of dissimilar adhesive joints subjected to cyclic ageing environments. The first step involved measuring the mechanical properties of the adhesive through tensile tests on unaged and cyclically aged dogbone specimens, considering their moisture content and ageing cycles. Based on the results, a degradable CZM was developed. To validate the numerical model, dissimilar double cantilever beam specimens (DCBs) of glass fibre reinforced polymer (GFRP) and aluminium were manufactured and tested before and after ageing. The load-displacement curves of the bi-materials bonded joints were successfully predicted using the developed model where the properties of the material are defined as a function of the moisture uptake and ageing cycles at each material element. The obtained results showed that after 4 ageing cycles, the maximum load of DCB specimens decrease considerably., Structural Integrity & Composites

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., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Structural Integrity & Composites, Adhesion Institute