Fatigue behaviour of butt-lap friction stir welded joints used with aluminum bridge decks

This paper presents the results of experimental tests and a numerical investigation of the fatigue behavior of buttlap friction stir welded (FSW) joints used in highway bridge decks made from aluminum extrusions. A large-scale fatigue experiment was designed to initiate fatigue failure in the butt-lap FS welds joining two full-scale aluminum extrusions used for highway bridge decks. Ten fatigue tests were carried out on an MTS servohydraulic press. Test results were used to analyze the fatigue failure mode of this unique joint type and to derive the S-N curve useful for the characterization and design of fatigue-sensitive details. The fatigue data was assessed using the effective notch stress (ENS) approach as recommended by the International Institute of Welding (IIW). Results show that the IIW design ENS IIW FAT-71 curve derived from fatigue tests on fusionwelded joints is conservative in assessing the fatigue behavior of butt-lap friction stir welded (FSW) joints, especially in the high cycle regime.