Practical Use of the Peak Stress Method for Fatigue Assessments of Steel and Aluminium Fillet-Welded Joints Subjected to Mode-I Loading

This work addresses the fatigue strength assessments of fillet welded joints made of steel or aluminium alloys and subjected to mode I loading in weld toe region where fatigue cracks nucleate. The proposed approach is based on relatively simple finite element analyses and combines the robustness of the Notch Stress Intensity Factor approach with the simplicity of the so-called ‘Peak Stress Method’. Fatigue strength assessments are performed on the basis of (i) a well defined elastic peak stress evaluated by finite element analyses at the crack initiation point (design stress) and (ii) a unified scatter band (design fatigue curve) dependent on the class of material, i.e. structural steel or aluminium alloys. The elastic peak stress is calculated by using rather coarse meshes with a fixed finite element size. A simple rule in order to calculate the elastic peak stress is also provided if a finite element size different from that used in the present work is adopted. The method can be applied to joints having complex geometry by adopting a two-step analysis procedure, which involves standard FE models like those usually adopted in an industrial context. The proposed approach is validated against a number of fatigue data published in the literature.