In the modern world more and more time and resources are being spent on alternative ‘green’ energy sources to replace the environmentally harmful fossil fuels that are more commonly used. One such method of creating energy in a clean, environmentally friendly way is through the use of wind turbines. These enormous windmills generate electrical energy by harnessing the power of the wind to spin the turbine blades which in turn drives a dynamo that generates the electricity.
As these wind turbines are constantly exposed to the elements, they’re commonly found on exposed hilltops or even out at sea as this is where the strongest winds are, they need to be well constructed and resilient enough to be able to generate power efficiently for a long period of time. A common material that the monopile type foundation structure for these offshore wind turbines is made out of is S355 Steel.
The welding process used in the construction of wind turbines attributes to fatigue and stress behaviours felt by the turbine in the future. A study conducted by Romali Biswal and Ali Mehmanparast of Cranfield University alongside Joe Kelleher of the ISIS Neutron and Muon Source aimed to investigate the influence of the welding process on the lattice formation as well as its effects on fatigue behaviour of the S355 welded joints. In-situ neutron diffraction measurements were undertaken on the cross weld specimens at room temperature under static and cyclic loading conditions to observe the progression of internal stress in different crystallographic planes located within the weld. Further tests relating to the hardness, microstructure and texture strength of the weld were undertaken to correlate the link between the material’s microstructure at the weld metal, heat affected zone and base metal with the mechanical response observed.
They found that lattice strains present were dependent on the orientation of the lattice plane of the crystal. Both the static and cyclic testing resulted in the {200} lattice orientation being the least load carrying capacity and the {211} lattice orientation was found to have maximum stiffness. The tensile test produced data that showed that the {110} and {200} lattice orientations result in 40-50% lower stiffness which means that joining of the weld metal and heat affected area could be prone to cracking.
These results are useful as they aid the understanding of what role the lattice deformation plays on the fatigue and fracture behaviour of the weldments present in the offshore wind turbine monopile foundations.
https://doi.org/10.1007/s11665-021-06104-5
