Fatigue of welded joints under multiaxial in- and out-of-phase local strains and stresses

The fact that conventional hypotheses are inadequate for evaluating welded joints subject to multiaxial outof-Phase stress/strain states with changing principal stress/strain directions made it necessary to develop a hypothesis on the basis that crack initiation is caused by local shear stresses and their mutual influencing in various directions of a surface element. The hypothesis of the equivalent effective stress (EES), which is based on local coordinate stresses in weld toes and considers the maximum stressed material volume governed by the stress gradient and the phase displacement between the local normal and shear stresses, transferred local multiaxial stress states for different load conditions with constant or changing principal stress directions into particular equivalent stresses. These values fitted fairly well into the particular local S-N curve determined under uniaxial load of the investigated welded flange-tube and tube-tube connections from the structural steel StE 460 .