Application of the Cohesive Sequential Static Fatigue algorithm to bonded joints considering the load-ratio effect

Debonding under fatigue loading is a common failure mode in adhesively bonded joints, where the load ratio (R-ratio) can significantly affect crack propagation behaviour. Accurately predicting fatigue crack growth, including the influence of the R-ratio, is crucial to ensure the safety and long-term reliability of these joints in structural applications. The objective of this study is to adapt the Cohesive–Sequential Static Fatigue (C-SSF) method, originally developed for delamination, to adhesively bonded joints under fatigue loading, with a particular focus on assessing its ability to capture the influence of the R-ratio. Published experimental results for Mode I and Mode II loading conditions are used to validate the accuracy of the C-SSF method in modelling fatigue-induced debonding across different R-ratios. The results demonstrate that the C-SSF method consistently captures the influence of the R-ratio on fatigue crack growth in adhesively bonded joints under both Mode I and Mode II loading conditions. Additionally, a numerical exercise is conducted on a non-standard specimen, revealing that when the maximum load is held constant, the crack growth rate decreases with increasing R-ratio. Overall, the C-SSF method exhibits significant potential as a numerical tool for simulating fatigue crack propagation in adhesively bonded joints under various loading conditions, including different R-ratios.