Combined loading effect on high cycle fatigue fracture behaviors of a stainless steel welded structure of elbow and socket

Abstract

In welded structures with complicated geometries and combined loading state, it is crucial to establish the criteria for fatigue failure. High cycle fatigue tests under combined loading states were performed using stainless steel sheets and welded specimens of elbow pipe and socket in this work. The cyclic stress–strain curve of the parent sheet were applied to the characteristics analysis of the welded specimens. Mode I or Mode I + III fatigue fracture occurred at the stress concentration part of the weld, and the crack starting point was different depending on the loading mode. The applied load was divided into bending and torsion for analysis, and the crack initiation was found on the side with the higher equivalent stress converted according to the Gough-Pollard failure criterion. The crack grew almost perpendicularly to the surface of the elbow pipe, and exhibited the appearance of a transgranular fracture. The fatigue limit based on the stress intensity factor (SIF) amplitude calculated by the proposed method using the strain energy release rate remained nearly constant even though the measured surface strain differed greatly. It is possible to predict the fatigue limit and life of similar structures by simplified models.