Transactions of Nanjing University of Aeronautics & Astronautics
Special Issue for Wind Turbine
A Fatigue Assessment Method for Composite Wind Turbine Blade
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Abstract:
Fatigue strength assessment of a horizontal axis wind turbine(HAWT) composite blade is considered. Fatigue load cases are identified and loads are calculated by GH Bladed software which are specified at the IEC61400 international specification and GL(Germanisher Lloyd) regulations for the wind energy conversion system. Stress analysis is performed with a 3-D finite element method(FEM). Take Saint-Venant’s principle into consideration, uniform cross section FEM models are built at each critical zone. Stress transformation matrix(STM) are set up by applied six unit load components on these models in the linear elastic range, and STM can be used to convert the load into stress components. The main material of composite wind turbine blade is fiber reinforced plastics(FRP). In order to evaluate the degree of fatigue damage of FRP, the well known strength criterion—Puck theory is used and the stresses of fiber direction are extracted. The total fatigue damage of each laminate on the critical point are counted by rain-flow counting method and Miner’s damage law based on general S-N curves. Several sections of a 45.3m blade were studied using the new fatigue evaluation method. A comparison of the performance of this method is made with a far more costly business software FOCUS. The fatigue damage of multi-axis FRP could be assessed conveniently by this FEM_STM method. This proposed method gives a reliable and efficient method to analyze the fatigue damage of slender composite structure with variable cross-sections.
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