Robust Mesh Insensitive Structural Stress Method for Fatigue Analysis of Welded Structures

Abstract

The design of welded structures and careful fatigue design evaluation is especially important in structural design since the stress concentrations at the welds have significant impact on the overall fatigue lives of the structures. Currently, the nominal stress or hot spot stress methods are widely used in the field for fatigue design evaluation. However, design based on these methods requires constructing separate S-N curves from the fatigue testing based on the joint geometry, loading, thickness, etc. It is also difficult to evaluate the fatigue performance using finite element analysis, where the calculated stress can vary according to element size, type, etc. To overcome these challenges, Battelle has developed a novel, mesh insensitive structural stress method (Verity ® ). The stresses are calculated using the balanced nodal forces and moments obtained at the weld toe location from the finite element solutions. Working with industry partners, Battelle has also developed a unified master S-N curve that combines the effects of joint geometry, loading modes and thicknesses. Battelle's structural stress procedure has been adopted as design weld fatigue codes by ASME Sec. VIII Div. 2 (ASME Boiler and Pressure Vessel Code) and API 579/ASME FFS-1 (Fitness-for-Service Evaluation). As a case study, the fatigue life prediction of a rectangular hollow section joint using a new structural stress method is presented in this paper.