Structural design and experimental investigation of a medium scale composite wind turbine blade considering fatigue life

The aim of this study was to make a structural design for development of a medium scale E-glass/epoxy composite wind turbine blade for a 750KW class horizontal axis wind turbine system. In this study, the various load cases specified by international specification IEC61400-1 and GL Regulations for the wind energy conversion system were considered, and a specific composite structure configuration which can effectively endure aerodynamic, centrifugal, hygro-thermal and mechanical loads and loads due to accumulation of ice was proposed. In order to evaluate the structure, a structural analysis for the composite wind turbine blade was performed using the finite element method (FEM). In the structural design, the acceptable blade structural configuration was determined through parametric studies, and the most dominant design parameters were confirmed. In the stress analysis using the FEM, it was confirmed that the blade structure was safe and stable in any of the various load cases. Moreover, the safety of the blade root joint with insert bolts, newly devised in this study, was checked against the design load and the fatigue. The fatigue life time over 20 years was estimated by using the well-known S-N linear damage equation, the load spectrum and Spera's empirical equations. With the results obtained from the structural design and analysis, the prototype composite blades were manufactured. The construction process and lay-up molding method developed in this study were employed to manufacture the prototype blades. Finally, a full-scale static structural test was performed with the simulated aerodynamic loads. From the experimental results, it was found that the designed blade had structural integrity. Furthermore, the measured results were in good agreement with the analytical results such as deflections, strains, the mass and the radial center of gravity.