Multiaxial fatigue of welded joints under constant and variable amplitude loadings

Abstract

Flange-tube joints from fine grained steel StE 460 with unmachined welds were investigated under biaxial constant and variable amplitude loading (bending and torsion) in the range of 10(3) to 5 x 10(6) cycles to crack initiation and break-through, respectively. In order not to interfere with residual stresses they were relieved by a heat treatment. In-phase loading can be treated fairly well using the conventional hypotheses (von Mises or Tresca) on the basis of nominal, structural or local strains or stresses. But the influence of out-of-phase loading on fatigue life is severely overestimated if conventional hypotheses are used. However, the hypothesis of the effective equivalent stress that is introduced leads to fairly good predictions for constant as well as for random variable amplitude loads. Therefore, the knowledge of local strains or stresses is necessary. They are determined by boundary element analyses that are dependent on weld geometry. This hypothesis considers the fatigue-life-reducing influence of out-of-phase loading by taking into account the interaction of local shear stresses acting in different surface planes of the material. Further, size effects resulting from weld geometry and loading mode were included. Damage accumulation under a Gaussian spectrum can be assessed for in- and out-of-phase combined bending and torsion using an allowable damage sum of 0.35

Fatigue damage criteria classification, modelling developments and trends for welded joints in marine structures

“…Adopting an effective equivalent stress hypothesis, only endurance is considered (e.g. Sonsino and Kueppers 2001;Sonsino and Lagoda 2004). Using a modified resistance (i.e.…”

Influence of Pitting Corrosion on Fatigue and Corrosion Fatigue of Ship and Offshore Structures, Part II: Load - Pit - Crack Interaction

“…However the condition da p /dt <da/dt is to be fulfilled during the whole crack propagation period. If it is not satisfied then pits will be formed on the crack path in the early phase of crack propagation, that was observed in some tests [8,36].…”

Mechanical characterization of yachts and pleasure crafts fillers

“…Most of the stressbased fatigue approaches were based on the assumption that load sequence effects are neglected and require the prescription of fatigue loadings, the availability of existing S-N curve database and the determination of stress concentration factor. The fatigue life of a structure under multi-axial loading has been estimated by methods based on principal stress ranges, effective stresses or stress states at different crack planes (Li et al, 2001;Sonsino and Kueppers, 2001;Van Dang et al, 2001;Yousefi et al, 2001). Different from the CFD method, the FCP approach is based on fracture mechanics and can take into account load sequence effects.…”