Design of Scaled-Down Composite I-Beams for Dynamic Characterization in Subcomponent Testing of a Wind Turbine Blade

Blade certification in the wind industry starts with coupon testing of materials and eventually culminates with full-scale blade testing. Coupon testing is not always representative of the materials’ performance and full-scale testing is expensive and time consuming. Subcomponent testing can bridge this gap and increase the assurance of blade manufacturers for introducing new materials and designs into wind industry. In this study, similitude theory is applied to the I-beam structure of a utility-scale wind turbine blade to design scaled down models that emulate the dynamic characteristics of the full-scale I-beam. The governing equations of motion for vibration of a thin walled laminated I-beam are analyzed to derive the scaling laws. Derived scaling laws are used as a design criterion to develop models that can accurately predict the fundamental frequency of the full-scale I-beam. Both complete and partial similarity cases are investigated. The distorted layup scaling technique is introduced as a novel approach to design scaled down composite models with totally different layups than the full-scale component. According to the results, depending on the desired size of the scaled models and ply scheme of the full-scale I-beam, models could be found with very good accuracy in predicting the fundamental frequency of the full-scale I-beam using derived scaling laws.