A degradable mode I cohesive zone model developed for damage and fracture analysis of dissimilar composite/metal adhesive joints subjected to cyclic ageing conditions

•Fracture of GFRP-to-Steel dissimilar bonded joints under cyclic ageing.•In cyclic ageing, the tensile strength of the adhesive decrease during the absorption and increase in the desorption process.•The sensitivity of the mechanical properties of the adhesive to the ageing cycles decreases with ageing cycles.•The numerical simulation based on CZM can precisely estimate the strength of cyclically aged adhesive joints.•The strength of DCB adhesive joints decreases significantly after the first absorption cycle. 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.