Fatigue behaviour of Al2024-T3 friction stir welded lap joints

The aim of this work is the characterization of the fatigue behaviour of AA2024-T3 friction stir welded overlap joints produced at German Aerospace Center (DLR) of Cologne (D). In these joints, two crack-like unwelded zones are present at overlap ends. The stress intensity factor at the crack tip and the fatigue crack path have been studied using the FE code Franc2d and the lifetime has been estimated by integrating the material propagation law with the software AFgrow, in which the stress intensity factor calculated with Franc2d was introduced. The numerical results predict lifetimes shorter than the experiments. This fact is attributed to an initial propagation in shear mode for a short distance, which was indeed observed with an optical microscope and it is predicted by mixed mode “failure mechanism map”.