On the interaction of axial and bending loads in the weld root fatigue strength assessment of load-carrying cruciform joints

Abstract Current design standards and recommendations incorporate the nominal stress system for assessing the fatigue strength capacity of load-carrying cruciform (LCX) joints with the fillet welds and failing from the weld root. Thus far, bending-loaded joints have not been addressed in these standards. The aim of the present study is to investigate the fatigue performance of LCX joints subjected to cyclic axial and bending loads. Firstly, fatigue test data sets of such joints subjected to axial loading and bending loads in the adjoined plate component are extracted from the literature, and statistical analyses are carried out to evaluate the fatigue strength capacity using the nominal weld stresses (NWSs). Secondly, experimental fatigue tests are carried out on LCX joints made of ultra-high-strength steel (UHSS) grade using constant amplitude loading and subjected to combined axial and bending load to study the load interaction effects on the fatigue strength capacity. The results showed that the FAT36 detail category for the weld root failures is applicable for bending-loaded joints when applying NWSs calculated on the basis of effective throat thickness of weld and assuming linear-elastic stress distribution over the joint section. The effective notch stress analyses showed unconservative results for the tested joints, when applying FAT225 design curve with the reference radius of r ref = 1.0 mm.