Overall description of main R&D challenges

• A prerequisite for a knowledge based reduction of wall thickness in cast components for wind turbines is a new prediction tool for fatigue design. The NTNU model “P•FAT” which predicts the probability of fatigue failures in components is still under development. A main R&D challenge is to further develop and adapt the model to be used in design of wind turbine cast iron components. In addition the lack of knowledge about the connection between casting defects and fatigue properties is an obstacle for cost reduction in the iron foundries. It is probable that todays requirements and specifications are unnecessary strict, but any reduction of these cannot be done without satisfactory documentation.
• This includes a number of R&D challenges:
• Further development and implementation of different models for crack growth, especially directed towards cast iron for wind turbine components.
• Demanding mechanical testing of samples from wind turbine components (including samples from disassembled wind turbines) with crack growth monitoring.
• Coupling of software for foundry technology simulations and fatigue design simulations.
• Handling of measured defect data and statistical variations.
• Handling of very large and complicated 3D geometries.
• Fatigue testing, including establishment of Wöhlerdata (S-N curve, fatigure limit) and crack growth data (da/dn vs. DK, DKth) for existing and future material grades.
  - Study crack growth associated with different types of defects in industrially cast samples where the defect distribution is known.
  - Study crack growth associated with unique and artificially introduced defects.
• Modelling of crack growth and comparison with measured data.
• Work out new design and quality criteria for wind turbine components.

Main goals

• Further development of the generic simulation tool P•FAT such that probability of fatigue failure of cast wind turbine components can be predicted based on defect distribution and crack growth calculations (probability calculations).
• Quantification of how different casting defects affect fatigue properties based on casting trials, fatigue testing and simulations in order to work out quality- and design criteria for cast iron wind turbine components