A numerical framework for determination of stress concentration factor distributions in tubular joints

Fatigue design of welded tubular joints implies the calculation of stress concentration factors at distinct weld toe locations using parametric formulas for basic loading cases. A Python based framework for automated calculation of hot spot stress and stress concentration factor distributions along the entire weld is presented. Hot spot stresses are calculated based on extrapolation of surface stresses extracted from a finite element analysis output database. For each node of the weld toes, the extrapolation direction and location dependent distances are first determined. Next the complete stress tensor in each read-out point is extrapolated towards the weld toe. The hot spot stress is determined as the maximum value of three critical stress values following the guidelines of DNV. A validation study is carried out in which the framework results are compared to both experimental data and parametric equations from literature for three different load cases: axial loading, in-plane bending and out-of-plane bending. The results obtained from the developed framework show good agreement with the experimental results and capture the shape of the stress concentration factor distribution much better than reference parametric equations. Finally, the framework is used to demonstrate the importance of including the weld geometry in the finite element model of the tubular joint. The results show that using a model without a weld can result in overly conservative estimations of stress concentration factors.

Publication year:2020

Accessibility:Open