Fatigue assessment of steel tube-to-flange welded joints with reinforcement ribs subjected to multiaxial loads according to the Peak Stress Method

Abstract

In fatigue design of welded structures, the Peak Stress Method (PSM) is a FE-oriented tool to estimate the Notch Stress Intensity Factors (NSIFs). In compliance with proper fatigue design curves validated against more than 1300 experimental data, the PSM allows to estimate the fatigue lifetime of welded structures made of either aluminium alloys or structural steels and subjected to uniaxial and multiaxial loadings. Moreover, an interactive analysis tool has also been developed in Ansys® Mechanical to automate PSM application on welded structures and support the FE analyst. In this work, the fatigue strength of complex steel tube-to-flange welded joints with reinforcement ribs has been experimentally investigated under pure bending, pure torsion and in-phase as well as out-of-phase combined bending-torsion loadings. The tested joint consists of a steel SHS tube having 6.3 mm thickness, which is joined at both ends to a 15-mm-thick flange. In addition, tube and flanges are joined by fillet welding to 6-mm-thick steel reinforcement ribs. A test rig has been designed in order to perform the experimental fatigue tests, taking advantage of two hydraulic actuators. The experimental fatigue results have been compared with fatigue lifetime estimations performed using the automated PSM tool.