Characterization of Cured Composite Materials for Wind Turbine Blades

Abstract

NCFs (Non-Crimp Fabrics) infused with epoxy resin are popular in the design of wind turbine blades and other complex systems due to their ability to conform to complex shapes. Past work in the development of a combination beam-shell modeling approach to simulate the forming of NCF composites has been demonstrated to capture the change in the orientations of the yarns during a forming process. The structural performance of these manufactured blades is often analyzed using finite element simulations that consider the material properties of the fibers and of the resin based on the rule of mixtures and orthotropic shells where the model is sectioned into zones that account for changes in the material properties due to variations in the orientations of the lamina and number of layers. With the availability of the beam-shell model, the use of zones can be removed if the individual contributions of the yarns (beam elements) and resin (shell elements) can be characterized and the orientations of the yarns resulting from a forming simulation can be used to account for the variations in the material properties of the composite throughout the blade. This research uses a combination of static flexure tests and impact modal tests to ascertain the material properties of the fibers and resin in a unidirectional and biaxial non-crimp fabric laminate plates. The material properties are used in a finite element model of the plate and the model is analyzed in flexure and in a free-free modal configuration to compare to experimental results. Two different approaches are used in the commercially available software Abaqus to model the plate. One approach uses a combination of beam and shell elements to represent the fibers and the resin, respectively. The other approach uses orthotropic shell elements to capture the unbalanced behavior of the fiber/resin composite. The beam/shell modeling approach better represents the overall behavior of a single-layer plate and can be extended to consider multiple plies.