The Modified Wöhler Curve Method applied along with the Reference Radius Concept to Design Welded Joints against Multiaxial Fatigue

In the present paper the accuracy of the Modified Wöhler Curve Method (MWCM) in estimating fatigue lifetime of welded joints subjected to multiaxial fatigue loading is investigated when this bi-parametrical critical plane approach is applied in conjunction with the reference radius concept. In more detail, local liner-elastic stress fields in the vicinity of weld toes are suggested as being determined by introducing a reference radius, rref, having length equal to 1mm, while the degree of multiaxiality and non-proportionality of the stress fields determined as above is directly taken into account through the MWCM itself. The accuracy and reliability of the devised multiaxial fatigue assessment technique was checked through several data sets taken from the literature and generated by testing steel and aluminium welded samples under in-phase and out-of-phase biaxial loading. Such a validation exercise seems to support the idea that the methodology formalised in the present paper can be considered as a reliable alternative to other existing approaches suitable for performing the fatigue assessment of welded connections subjected to in-field multiaxial loading paths. The level of accuracy obtained is promising also because, thanks to its nature, the MWCM can be used to design welded components against multiaxial fatigue not only by applying it along with the rref=1mm concept, but also, as proven elsewhere, in terms of both nominal and hot-spot stresses: this implies that the same multiaxial fatigue damage parameter can successfully be employed to address problems of practical interest by taking full advantage of any of the three different methods suggested by the Fatigue Design Recommendations of the International Institute of Welding (IIW) to perform the stress analysis in the absence of cracks