Prediction of service fatigue strength of a welded tubular joint on the basis of the notch strain approach

The applicability of the notch strain approach to the assessment of the fatigue strength and service life of a K-shaped tubular joint is investigated. The structural stresses in the hot spot area are calculated by the finite element method and compared with the results of relevant parametric formulae as well as of strain gauge measurements. The stress concentration factor at the weld toe is determined on the basis of a plane cross-sectional model of the weld at the hot spot. The elastic-plastic notch strains are derived therefrom using the cyclic stress strain curve of the material (finite element results and approximations according to Neuber and Sonsino). The fatigue strength of the tubular joint under constant-amplitude loading is predicted on the basis of the strain S-N curve. The service life under variable-amplitude loading in seawater is derived using the Miner rule. The notch strain approach for welded joints results in unacceptably large differences in the predicted strength and life values under similarly acceptable assumptions in respect of material state, local hardness and residual stress. The inhomogeneity of material and hardness at the weld toe seems to be the main reason for the discrepancies. (C) 1998 Elsevier Science Ltd.