Low-cycle fatigue life prediction of fillet-welded joints in ship details

Welded joints in ship structures are subject to several variable loadings which may lead to fracture after a relatively low number of cycles. This behaviour is not always fully described by high-cycle fatigue predictions, so low-cycle fatigue has also to be assessed, considering plastic deformation. Local approaches are applied in these cases and are mainly based on local displacement and strain measurements by strain gauges. These approaches have physical limitations when high stress concentrations regions have to be analyzed. The aim of the present research activity is to predict the low-cycle fatigue life of fillet welded joints using the notch strain approach. Elastic-plastic finite element analysis (FEA) was performed, using different cyclic stress-strain curves for base material, heat affected zone and weld metal. Three models of the welded specimen were considered in the FEA: the first model refers to nominal dimension, the second one to the measured thicknesses of the plates and the third model to the geometry acquired by means of a 3D scanner. The finite element analyses were validated by the experimental data. Effective notch strain values from fro FEA were used to predict fatigue life. The proposed method gave interesting information about fatigue life of fillet welded joints used in ship structures.