Prediction of Fatigue Crack Propagation in Friction Stir Welds

摘要

"Inspections or other procedures must be established as necessary to prevent catastrophic failure, and must be included in the Airworthiness Limitations Sections" [1]. The recent FAR regulations for damage tolerance and fatigue evaluations of aircraft structure require fatigue crack growth predictions. If friction stir welding is considered for primary aircraft structures, the prediction methodologies have to be adopted for this specific joint type. In this paper the predicted crack length versus cycles curves obtained from two widely used software packages, ESACRACK and AFGROW, are compared to experimental results. Fatigue experiments were performed in order to characterize the fatigue crack growth behavior of AL2024A-T3 and AL6013-T6 aluminum alloys and to have a comparison with the simulation results. Following joint configurations and loading types are considered: crack growth parallel to the weld, crack in the nugget, constant amplitude loading/crack growth parallel to the weld, crack in the nugget, periodic tensile overloads/crack perpendicular to the weld, constant amplitude loading. It is shown, that good predictions are obtained, if the residual stresses are added to the external loads.