Abstract
The aim of this research was to develop a reliable predictive fatigue damage model for adhesively bonded structures. It was necessary for such a numerical model to be independent of geometry of the structure and capable of considering different fatigue damage phases, of simulating the experimentally measured damage evolution and of predicting the effect of main fatigue loading characteristics. Three different adhesively bonded joints, namely the single lap joint, the laminated doubler in bending and the mixed-mode flexure specimen manufactured with the same adhesive system were considered for experimental and numerical investigations. The bonded joints were tested under quasi-static and fatigue loading and the failure responses of the bonded joints were studied experimentally and modelled numerically. To assess static and fatigue progressive damage in the bonded joints, experimental approaches, including backface strain and video microscopy techniques were employed. The effect of important fatigue loading parameters including the maximum fatigue load level and the load ratio on the failure behaviour of the bonded joints was examined experimentally. A cohesive zone model with a bi-linear traction-separation response was used to simulate the progressive damage in the adhesively bonded joints. This cohesive zone model was integrated with a damage mechanics based fatigue model to simulate the deleterious influence of fatigue loading. The proposed fatigue damage model was able to account for the effects of fatigue loading characteristics including the maximum fatigue load and fatigue load ratio. The static and fatigue damage models were calibrated, validated and optimised against the experimental results obtained and other published experimental data. The fatigue damage model was applied to adhesively bonded joints subjected to constant and variable amplitude fatigue loading. The model was able to successfully predict the detrimental effect of the variable amplitude fatigue loading as well as the constant amplitude fatigue loading. The proposed fatigue damage model was generally found to be a significant improvement on other damage models available for adhesively bonded structures.