Strain-based fatigue reliability assessment of welded joints in ship structures

Abstract

A strain-based fatigue reliability assessment of welded ship structural joints is presented. To obtain a complete description of the fatigue stress acting on a butt-welded joint in a ship, a probabilistic distribution for the low cycle fatigue stress range is developed considering the uncertainty in the static and dynamic stresses. A model considering the effect of a secondary notch embedded into the primary notch is developed considering the low and high cycle fatigue regimes. The misalignment, secondary notch, residual stress and fatigue limit effects are incorporated into the notch strain approach on which the fatigue reliability assessment is based in the present study. The efficient Advanced Mean Value method is used to derive the distribution of the fatigue crack initiation life where a detectable crack is formed. The influence of different modelling options is analysed, and the importance of accounting for the misalignment, residual stress and especially the proposed secondary notch effect is discussed. The sensitivity of the reliability estimates to the variables’ uncertainty is investigated based on the First Order Reliability Method, and the dominant ones are identified.