Experimental Measurement of Sectional Stiffness Properties of Composite Rotor Blades

This paper describes an experimental-numerical technique for evaluating the full 6 × 6 stiffness matrices for beams based on measured strains using digital image correlation (DIC). The general formulation makes the method well suited for isotropic beams with simple cross-sectional configurations or beams made of anisotropic materials with complex geometries, as typically exhibited in composite rotor blades. A 2-D finite element code, SectionBuilder, is used to generate a finite element mesh of the cross-section and evaluate the warping field, which is then combined with the experimental strain data to calculate the stiffness matrix. A detailed error analysis is performed to allow for the propagation of the experimental errors into the stiffness calculation and provide an uncertainty quantification for use in comprehensive analysis codes. Experimental results are presented for an isotropic beam and two composite rotor blades. Overall, the stiffness properties from the experimental measurements and numerical models showed good agreement and the experimental measurements were able to capture all the expected non-zero stiffness components.