Towards an advanced fatigue assessment of welded steel joints with multiaxial stress states

Advanced fatigue assessment methods, e.g. the Two‐Stage‐Model, are needed for the design of complex constructions or to accurately evaluate the remaining fatigue life of existing structures. The applicability of the Two‐Stage‐Model, including strain‐life approach and linear elastic fracture mechanics, was experimentally validated for uniaxial stress states only. However, typical construction details of steel and composite structures often exhibit a multiaxial non‐proportional stress state, which leads to variable principal stress values and directions. Comprehensive extensions of the Two‐Stage‐Model from uniaxial to multiaxial stress states are missing so far. This paper shows a study on advanced approaches that incorporate multiaxial stress states for both the crack initiation stage and the crack propagation stage, and their application in the Two‐Stage‐Model. For crack initiation, several approaches for the strain‐life approach, including multiaxial non‐proportional hardening and damage assessment based on critical planes are evaluated with respect to an application on the strain‐life approach. For the extension of the crack propagation stage, a computational procedure using XFEM and mixed‐mode approaches is presented.