On the accuracy of nominal, structural, and local stress based approaches in designing aluminium welded joints against fatigue

This paper investigates the accuracy and reliability of nominal stresses, hot-spot stresses, effective notch stresses, notch-stress intensity factors (N-SIFs) and material length scale parameters in estimating fatigue lifetime of aluminium welded joints. This comparative assessment was based on a large number of experimental data taken from the literature and generated by testing, under either cyclic axial loading or cyclic bending, a variety of aluminium welded structural details. Whenever it was required, stress analyses were performed by solving bi-dimensional linear-elastic finite element models. The obtained results demonstrate that the effective notch stress method, the N-SIF approach, and the Theory of Critical Distances (TCD) provide a more accurate fatigue life estimation in comparison with the other methodologies. In this context, the TCD was seen to be easier to adopt, requiring less computational effort than the effective notch stress method and the N-SIF approach. Finally, based on the experimental results being re-analysed, a unifying value of 0.5 mm is proposed for the TCD critical distance, with this value allowing aluminium welded connections to be designed accurately irrespective of joint geometry's complexity.