DTU Mechanical Engineering has a strong tradition of professional collaboration enabling world-class research into materials modelling on every level—ranging from the atomic level to full-scale tests test beds. The collaboration offers multiple future opportunities, among other things concerning research in hard materials, where 3D modelling and 3D materials characterization are combined in connection with new facilities such as ESS, European Spallation Source, and MAX IV in Lund.
REWIND Center: Integrated materials modelling of wind turbine components
Three sections at the department—the Section of Manufacturing Engineering, the Section of Materials and Surface Engineering, and the Section of Solid Mechanics—already have a strong collaboration within materials modelling, among other things in connection with the REWIND Center, which was established in early 2011 and is funded by the former Danish Council for Strategic Research, currently Innovation Fund Denmark
Research at REWIND has focused on identifying the link between the materials selection, process selection, and what happens to the metallic wind turbine components in the nacelle during the very heavy mechanical loads to which they are exposed when the wind turbine is in use. A wind turbine is exposed to loads imposed by wind and gravitation—and both in combination with the rotor’s revolutions and in interaction with the generator in the nacelle. Heavy loads can lead to early fracture of the individual components, or major breakdowns of the entire wind turbine.
Photo: Colourbox.
The reason for the problems is often to be found in the way the components were originally designed and manufactured, as this significantly affects material behaviour during operation. This could, for example, be the casting of the rotor hub and main shaft, and the forging of main bearings and gear parts. Casting and forging are processes which inherently cause unhomogeneous internal structures in the materials, and the resulting stress concentrations may impact components negatively during subsequent use. The research conducted at the centre is thus based on the entire chain—materials, processes, components, loads, and performance—to ensure the entire wind turbine’s increased long-term reliability and durability.
Newly developed materials models provide insight into component performance and service life
Since the REWIND Center was established in 2011, the different research projects have provided new insight into and better understanding of the interaction between materials, manufacturing processes, and subsequent loads. Specifically, this means, for example, that numerical models have been developed for simulation of the manufacturing processes as well as materials behaviour for the metal parts of the wind turbine’s hub and drivetrain which are subjected to heavy loads. Models have also been developed for the reliability and expected service life of the materials on the basis of mechanical tests and examinations of micro-mechanical defects.
Finally, models have been developed to describe the relationship between different surface treatments and the microstructure of the material and their influence on the mechanical properties. Through numerical modelling and experimental observations, improved understanding has also been obtained of how a fatigue fracture occurs. This has been done by means of utilizing results from the models developed for the casting and forging processes, which have provided new input to the fatigue analysis thereby enabling more resalistic prediction of the mechanical properties of the final components.
The many new models constitute tools which will help ensure a much better understanding of the performance and service life to be expected in relation to the various components of the wind turbine.
“The development of the models is based on a wish to describe the underlying multi-physical conditions, i.e. heat transfer and thermodynamical, solid, fluid, and material-mechanical issues, and this requires strong collaboration between the different sections here at the department,” says Jesper Hattel, Professor, leader of the REWIND centre and Head of Section of Manufacturing Engineering.
Modelling and new test facilities
To ensure that models for material behaviour are as accurate as possible under different conditions and loads, it is essential that they are adjusted according to the information gathered from experiments and test set-ups. DTU has established a unique facility for this purpose, i.e. the CASMaT, Villum Center for Advanced Structural and Material Testing, at DTU, where materials and components can be studied—ranging from full-scale level tests on, for example, wind turbine blades, to tests at micro-scale and nano-scale level in connection with electron microscopy.
“The Villum Center is an important element in the overall picture,” says Christian Niordson, Professor and Head of Section of Solid Mechanics. “Here we can carry out full-scale tests of the components and subject them to heavy loads to get insight into fracture mechanisms and mechanical properties.”
CASMaT: Test setup with a wing from a windturbine. Photo: Flemming Jørgensen.
As part of the collaboration, the researchers will also have access to the new facilities in Lund, ESS, and MAX IV, which will increase the possibilities of adapting the materials models developed at DTU based on validation of all scales from atomic to micro-level.
“The large international wave within materials research is integrated computational materials engineering, which means that you increase the use of materials modelling for designing materials from atomic level to macro-scale level to reduce the use of the trial and error methods, which was previously the standard procedure for development of new materials and processing into new products,” says Marcel Somers, Professor and Head of Section for Materials and Surface Engineering.
“This requires that we have reliable materials models, which is why theyare in focus; experimental test facilities such as CASMaT, ESS, and MAX IV are indispensable for the validation and optimization of the numerical models.”
Digitalization and modelling
Once the materials models have been developed, they can be used to predict how a material will behave under certain manufacturing conditions, and later how the manufactured component behaves under different loads when it has been taken into use. This chain constitutes a key part of what is known as the component’s digital twin.
“The three sections MPP, MTU, and FAM look at the physical product and the digital representation of it using the numerical models,” says Jesper Hattel. “The manufacturing at system level with the description of product flow and the associated planning, on the other hand, is handled by P&K as well as DTU Management Engineering. We look at the production chain, i.e. from manufacturing where design, materials, and production methods are chosen, to the actual manufacturing and use of the product or the component.”
llustration of the physical and digital twin part, illustration by Professor Jesper Hattel.
When talking about the digital twin, it is not only in relation to the component or product itself, but the entire context of which it forms part. Therefore, there is wide scope for materials modelling in connection with digitalization of the manufacturing industry. An overview of the manufacturing process in real time can be provided by incorporating new designs on a regular basis and testing designs and components virtually before they are manufactured and put into service, and the manufacturing itself can be adjusted as faults are detected.
Facts about CASMaT
CASMaT, Villum Center for Advanced Structural and Material Testing, is a partnership between DTU Mechanical Engineering, DTU Wind Energy, and DTU Civil Engineering. The establishment of the test centre was funded by a DKK 76 million donation from VILLUM FONDEN. The centre equipment partly consists of equipment donated by VILLUM FONDEN and partly of existing DTU equipment. DTU and the Danish Building and Property Agency provide funding for the two new buildings constructed at Lyngby and Risø campuses. Read more about CASMaT.