Fatigue Behaviour of Al 6082-T6 Friction Stir Welded Tubular Joints under Torsional Loading

The aim of the present research is to investigate the fatigue behaviour of friction stir (FS) welded tubular joints in aluminium alloy subjected to torsional fatigue loading. To manufacture the samples which were tested, an MTS I-STIR process development system was equipped with a retracting tool specifically designed for these tubular welds. Al 6082-T6 FS welded samples were tested under cyclic torsion with a nominal shear stress ratio equal to -1 and 0. The test data show that, strictly speaking, the presence of non-zero mean shear stresses has a detrimental effect on the overall torsional fatigue strength of the FS welded joints. However, the reanalysis discussed in the present paper suggests that, from a statistical point of view, any detrimental effect is small. This means that fatigue assessment under torsional fatigue loading of these FS welded tubular connections can be performed with little loss of accuracy by neglecting the presence of non-zero mean shear stresses.