Fatigue life assessment of fillet welded joint using the local strain approach accounting for microscale notch effect

The study aims to develop a local strain-based approach to consider the effect of microscale notches around the weld toe on the fatigue life of welded joints. The strain-life curve of the local strain approach was modified according to a roughness parameter, and the modified strain-life curve was validated using existing fatigue test data of specimens with rough surfaces. 3D scans with two levels of resolutions, microhardness measurements and residual stress simulations of a series of fillet welded joints were carried out to determine the inputs of the local strain-based approach. The 3D finite element method and the equivalent strain energy density approach were used to determine the elastic and elastic-plastic local stress-strain at various locations along the weld seam. The fatigue crack initiation life of the fillet welded joints is estimated considering the effects of the weld geometry with the microscale notch, residual stress, and material property and compared with experimental data. The results indicate that the fatigue life estimation of the welded joints was satisfactory. The microscale notch around the weld toe is evident, and its effect on the fatigue life is significant. • An explicit model of the microscale notch effect on the fatigue strength of welded joints is presented. • The strain-life curve is adjusted based on the state of surface roughness. • Two 3D scans captured macroscale and microscale weld toe characteristics. • The suggested methodology was validated.