Comparison of Fatigue Life of K Joints with and Without Overlap Using 3D Fatigue FEM Analysis

Tubular members are extensively nowadays used in the construction of many vehicles due to their excellent properties like high torsional rigidity, high strength to weight ratio, and less surface area. Also, it helps in reducing expenditure during the fabrication and installation of the big effective designs. The tubular members are subjected to different cyclic forces leading to plastic deformation of chords, material degradation, fatigue cracks due to which tubular members undergo severe damage, and finally, will lead to the failure of the whole structure. The overlapped tubular joints and simple gap joints can be used as the joint type in tubular members. In this study, the fatigue analysis of overlapped and non-overlapped K-type tubular joints was carried out using the 3D fatigue FE analysis method to investigate the fatigue performance. The 3D fatigue FE analysis based on continuum mechanics and elastoplastic cyclic hysteresis constitutive equations was carried out in 3 steps. Firstly, thermal load i.e., temperature histories, were calculated using thermal analysis secondly welding residual stress and welding deformation were estimated using thermal load as initial data in the mechanical analysis. In the 3rd step, the residual welding stresses and welding deformation were utilized as initial data to determine the fatigue life The S-N curve was drawn from 3D fatigue FEM analysis results.