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Similitude Analysis of the Strain Field for Loaded Composite I-Beams Emulating Wind Turbine Blades



The characterization of new materials for the large wind turbine blades starts with the testing of material coupon and culminates with the full-scale testing of a blade using these materials. Coupon testing is a cost-effective means to characterize a material, but it is not necessarily representative of the structural performance of the blade. Thus, expensive and time consuming full-scale testing is the current means for demonstrating the capabilities of a material system for wind turbine blades. Subcomponent testing has the potential to bridge the gap between the coupon and full-scale tests. To develop a subcomponent test, similitude analysis is utilized to design scaled models that are accurate representations of their parent full-scale component. In this study, a similitude analysis is developed to design the scaled-down models for the I-beam geometry of a utility-scale wind turbine blade. Similarity of the strain field between scaled models and the prototype is investigated to design the scaled-down I-beams for characterization of the structural performance of the new materials. The scaling laws for strain distribution on the flanges of the I-beam are derived and used as a metric to design models with different scales and lamination schemes that withstand the same strain field as the prototype under adjusted loads. The designed models are manufactured and loaded using a three-point bending test. Digital image correlation is used to measure the full-field strain distribution in the flanges of the models. Measured strain distribution for incremental loads is used to verify the analytical and finite element models. The strain distribution of the prototype is predicted with the analytical model and compared to the experimental values to demonstrate the similarity of the strain field between model and prototype.

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