Fatigue analysis of composite bonded repairs

The present work intends to describe all procedures developed in order to predict the fatigue/fracture behaviour of single-strap repairs of carbon-epoxy composites. The main goal is to validate a mixed-mode I + II cohesive zone model for high-cycle fatigue based on the modified Paris law. A preliminary static fracture characterisation in mode I, mode II and mixed-mode I + II is necessary in order to achieve the static energetic criterion describing fracture of the bonded joint. Subsequently, the same tests were carried out under high-cycle fatigue loading in order to determine the evolution of the modified Paris law parameters as function of mode ratio. These fatigue/fracture characterisation tests were also used to validate the cohesive mixed-mode I + II zone model appropriate for high-cycle fatigue. The model was then used to predict fatigue life of the single-strap repairs and revealed good performance when compared with experimental results. Finally, the model was utilised to assess the influence of specimen geometry on the fatigue life of these structural repairs. It was concluded that such type of models can be considered appealing tools concerning the optimisation of repaired structures fatigue life.