Prediction of hot spot stress distribution for tubular K-joints under basic loadings

Abstract

In the fatigue life assessment of tubular joints subjected to cyclic loading, the hot spot stress at the weld toe is critical for determining the number of cycles that the tubular joints can sustain before fatigue failure. Although there are many reported parametric equations of the stress concentration factor (SCF) for predicting tubular joints subjected to basic loadings, i.e. axial loading (AX), in-plane bending loading (IPB) and out-of-plane bending loading (OPB), it is not accurate for estimating the hot spot stress value of a tubular joint subjected to complex loading only from a superposed stress result from a combination of two or three basic loadings because the peak stresses at the weld toe for a tubular joint subjected to different basic loadings are not located at a fixed position. To calculate an accurate peak stress value along the weld toe for a tubular joint subjected to complex loading, it is necessary to know accurate stress distributions of the tubular joint under three basic loadings. Then the stress distribution of the tubular joint subjected to combined loading can be obtained from a superposition of stress distributions of two or three basic loadings. Then the peak stress is easily located from such a stress distribution. The stress distributions of uni-planar tubular K -joints under three basic loadings are analyzed using a finite element method in this study, and the influence of geometrical parameters on the stress distributions is also investigated. Based on the numerical results of 287 K -joint finite element models, a set of parametric equations for calculating the stress distribution of a K -joint under AX, IPB and OPB respectively are presented using a curve fitting technique. The accuracy of the proposed parametric equations is evaluated by comparing the predicted stress distribution results with the analyzed finite element results, and it is found that the parametric equations are reliable and accurate for calculating the stress distributions along the weld toe for K -joints under basic loadings.