Through thickness fatigue strength variation in thick S460 plates
A. Mohabeddine 1, 2, K. Creusen 3, J. Winkes 3, J.A.F.O. Correia 4, M. Veljkovic 1
1 Faculty of Civil Engineering and Geosciences, Delft University of Technology, the Netherlands
2 Faculty of Engineering, University of Porto, Portugal
3 C1 Connections, the Hague, the Netherlands
4 INEGI & CONSTRUCT, Faculty of Engineering, University of Porto, Portugal
Steel thick plates (i.e. thickness > 80 mm) are increasingly used in wind turbine offshore structures. The fracture toughness of thick plates is well addressed in the literature; however, little is known on their fatigue resistance. Thick plates exhibit distinct features that can present additional structural integrity issues compared to conventional thin steel plates, caused by the significant plane strain effects, heterogeneous through-thickness micro structures and mechanical properties, and inherent larger material defects. This paper presents a comparison between the fatigue resistance of two distinct regions in a 100 mm thick steel slab, namely, the surface region and the core region. High cycle fatigue experimental tests are performed under force-controlled condition for both regions using dog-bone small-scale specimens. Large material defects are observed in the core region. The fatigue results of surface specimen show longer fatigue life compared to core specimens. Large scatter of the data is present in core specimens due to the presence of large voids. The fracture patterns of the different specimens are identified through light and scanning microscopy. Statistical analysis of the fatigue data is conducted, and a fatigue S-N curve is derived when applicable.
Key words: Fatigue, high-strength steel, thick steel slabs, defects, statistical evaluation, S-N curves