Fatigue performance of tubular X-joints with PJP+ welds: II — Numerical investigation

•Fatigue cracks in tubular joints propagate in a mode I dominant direction.•The crack front for realistic fatigue cracks differs from a semi-elliptical shape.•Typical fatigue cracks in tubular joints experience high crack-front constraints.•Multiple cracks with overlapping crack faces delay the fatigue crack propagations.

This paper summarizes the numerical investigation on the fatigue crack propagation in CHS X-joints under constant amplitude brace in-plane bending, in parallel with the experimental investigation reported in the companion paper. The finite element procedure examines the effects of the crack propagation angle, the crack-front profile and the interaction between adjacent fatigue cracks on the fatigue driving force, measured by the stress-intensity factors. The Paris type estimation provides a close prediction on the propagation life of weld toe cracks observed in the experiment. The initiation of the root crack, based on the Paris prediction, occurs much later than that of the toe crack.