Similitude Analysis of Composite I-Beams with Application to Subcomponent Testing of Wind Turbine Blades

The mechanical behavior of new materials for wind turbine blades is initially characterized by using coupon testing. If the results of the coupon testing look promising, then the materials are incorporated into a blade and certified through a full-scale blade test. The coupon testing is not always representative of performance of the new materials, and full-scale-blade testing is time consuming and very expensive—on the order of several hundred thousand dollars. To bridge the large gap between coupon testing and a full-scale test, subcomponent testing is proposed as a cost-effective alternative. To design a meaningful scaled-down subcomponent emulating the structural conditions experienced in the full-scale component, it is proposed that similitude theory can be applied to a scaled replica of the I-beam structure of a wind turbine blade involving spar caps and the shear web. In the current research, the governing equations for the bending of a simply-supported shear deformable thin-walled composite I-beam are analyzed to derive the scaling laws. Fidelity of the derived scaling laws is then examined as a model-validation criterion by mapping the maximum deflection of variant subcomponents to the full-scale composite I-beam. The combined effects of the size of the subcomponents and the ply stack-up schemes on the fidelity of the scaling laws are then investigated through complete and partial similarity conditions. According to the results, preserving the aspect ratio plays a critical role in successful prediction of the maximum bending of the full-scale I-beam. Also, subcomponents with a modified ply stack-up could be found with good accuracy in maximum bending prediction using the derived scaling laws.