Effect of non-proportional stress states caused by varying phase shifts on the fatigue life of welded joints

In this paper, the effect of multiaxial non-proportional stress states on the fatigue life of welded joints is investigated. The non-proportional stress states are caused by various phase shifts between the normal and shear stresses. In total 45, welded tube-to-tube specimens are tested under multiaxial proportional and non-proportional loading. The increase in fatigue damage caused by non-proportional stresses, compared to proportional stresses, is quantified by penalty factors. A set of penalty factors are derived from the fatigue experiments for use with the governing multiaxial fatigue criteria by the International Institute of Welding (IIW) and Det Norske Veritas (DNV). The experimental results show that phase shifts decrease the fatigue life. However, this reduction is not to the extend proposed by the governing guidelines. Furthermore, the results indicate that different degrees of phase shift do not induce varying levels of fatigue life degradation.