The present paper addresses the problem of designing aluminium friction stir (FS) weldedudjoints against multiaxial fatigue. After developing a bespoke FS welding technologyudsuitable for joining aluminium tubes, some one hundred welded tubular specimens of Alud6082-T6 were tested under pure axial, pure torsional and biaxial tension-torsion loading.udThe influence was explored of two independent variables, namely the proportional or nonproportionaludnature of the biaxial loading and the effect of axial and torsional non-zeroudmean stresses. The experimental results were re-analysed using the Modified WöhlerudCurve Method (MWCM), with this bi-parametrical critical plane approach being applied inudterms of nominal stresses, notch stresses, and also the Point Method. The validationudexercise carried out using these experimental data demonstrated that the MWCM isudapplicable to prediction of the fatigue lives for these FS welded joints, with its use resultingudin life estimates that fall within the uniaxial and torsional calibration scatter bands. Theudapproach proposed in the present paper offers, for the first time, a complete solution to theudproblem of designing tubular FS welded joints against multiaxial fatigue loading. ud
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