Comportamento a fatica multiassiale di unioni saldate in acciaio e lega leggera in funzione dell'energia di deformazione locale

The local criterion based on the Notch Stress Intensity Factors (NSIF) set equal to zero the weld toe radius and allow us to summarise a large body of experimental data related to cruciform and T-shaped welded joints (with main plate and transverse plate thickness ranging from 6 to 100 mm and from 3 to 220 mm, respectively) in a single scatter band when plotted as a function of the Mode I NSIF. The synthesis needs the constancy of the opening angle at the weld toe. In order to overcome this limitation and make it possible a synthesis varying the opening angle as well as the position of fatigue crack initiation points (at the weld toe or the weld root), the mean value of the strain energy density AW can be used. This energy is evaluated in a structural volume having a radius equal to 0.28 mm or 0.12 mm for welded joints made of structural steel or aluminium, respectively. The paper extends the strain energy density criterion to the welded joints under multiaxial loading conditions (Mode I, traction or bending, plus mode III, torsion). The values for ΔW are found to be in agreement with those already reported in the literature for welded joints under traction or bending loading conditions.