Analysis of the thickness effect in thin steel welded structures under uniaxial fatigue loading

This paper investigates the scale effect in relatively thin welded joints subjected to fatigue loading made of steel. In the scientific literature, the fatigue behaviour of arc-welded joints is usually divided into two groups: thick and thin joints. A cut-off thickness, typically in the range of 13-22 mm, was introduced; under such cut-off value, the design fatigue strength does not increase when the thickness is decreased. Despite this common approach, in this paper, the concept of cut-off thickness is revised and a numerical procedure is proposed, regardless of the thickness of the joint, by means of the implicit gradient method. Classical non-load-carrying and load-carrying cruciform joints made of steel are considered in the three-dimensional numerical analysis. Finally, the fatigue behaviour of joints two millimetres thick with a longitudinal or transversal stiffener was also analysed by means of the implicit gradient approach. The Woehler curve was evaluated in terms of the nominal stress of such a series and a good correlation was found with experimental data by using the numerical procedure optimised for thick welded joints.