Most ship structures consist of plate details, connected to longitudinal and transverse members by welded joints, which are the sites of high stress concentrations, and are subject to severe environmental loading from wave pressure, ship motions and loading/unloading operations, which induce significant fatigue loads. The presence of stress concentrations and fatigue loads leads to cyclic stress that exceeds the yield stress locally and some cracks, related to low cycle fatigue (LCF), have been detected in ship structures.

The complexity of the real ship details and loading conditions creates some problems to the designer in the evaluation of this phenomenon and the fatigue life of the ship structures.

From an engineering point of view, the fatigue data obtained by means of tests are useful only if these values can be extended from the small specimens, generally used in the laboratory experiments, to real structural details subjected to complex loading conditions.

In this study the LCF strength of ship welded structures was analysed on the basis of experimental investigations carried out on large- and small-scale fatigue specimens in order to find a correlation between the obtained results. An experimental set-up was planned and realized for the large-scale fatigue tests on a ship structural detail. This concerns the experimental tests on specimens (base material and welded joints), the thermographic and digital image correlation techniques were applied to detect temperature and displacement patterns during the tests. Moreover extensive finite element analyses of the investigated detail were performed for the analysis of stress pattern at the sites of high stress concentrations.

Aim of this research was the development of a theoretical model, based on the scale effect, for the strength assessment of ship details under LCF loading.