Notch stress intensity factors and fatigue strength of aluminium and steel welded joints

According to a recent and appropriate definition, stress field parameters, namely notch stress intensity factors (N-SIFs), can be used to predict the fatigue behaviour of mechanical components weakened by V-shaped re-entrant corners, where the singularity in the stress distribution makes any failure criterion based on elastic peak stress no longer applicable. Commonly thought of as parameters able to control the fatigue crack initiation life, N-SIFs are, under certain circumstances, also useful for predicting the component total fatigue life. The fatigue strength of aluminium welded joints with different geometries and thicknesses are summarised in a single scatter band by using an N-SIF-based approach. The statistical analysis is carried out taking into account experimental data already reported in the literature, referring to welded joints with a thickness ranging from 3 to 24 mm. Results of steel and aluminium welded joints are then compared: at high number fatigue life, the relative fatigue strength is slightly greater than 2, in agreement with the value previously reported in the literature for butt spliced bolted joints. The value of the theoretical exponent quantifying the scale effect (0.326 against 0.25 suggested by Eurocodes) is discussed.