Fatigue Reliability Assessment of Fillet Welded Cruciform Joints Based on the Fatigue Notch Factor and Local Strain Approach

The objective of this work is to analyze the fatigue reliability of fillet welded cruciform joints considering the uncertainty of the load and capacity. The weld shape is defined by multivariate normally distributed variables, which represent the position variations of the shape control points on the fillet welds. Finite element analyses are performed to calculate the fatigue notch factors of the weld root and toe, where the fatigue crack is usually initiated. Various weld shapes associated with various correlation conditions and weld quality levels are generated and the corresponding probability distributions of the fatigue notch factors are obtained by using the Monte Carlo simulation method. Sensitivity analyses are carried out to identify which location is more important for the fatigue notch factors. Within the context of the local strain approach, a critical fatigue notch factor that can exactly trigger fatigue failure is proposed. Its statistical descriptors are determined by using the Monte Carlo simulation method, in which the nominal stress range, material properties and fatigue damage at failure are treated as random variables. The limit state functions of the weld root and toe are formulated based on the actual and critical fatigue notch factors. The first order reliability method is applied to evaluate the fatigue reliability. The cruciform joint, composed by two fatigue-prone locations, is evaluated as a series system of components. Two different loading conditions, which make the cruciform joints load-carrying and non-load-carrying respectively, are considered.