Flexural-twist coupling of anisotropic beams

Flexural-twist coupling is significant in many aerospace structures. This paper investigates the flexural-twist coupling of CFRP beams of varying lay-up from experimental, simple analytical, and finite element approaches. Although the computational capability now exists to undertake dynamic analyses of large composite structures using detailed 3-dimensional finite element models, such analyses are still too time consuming for use in design optimisation. The behaviour of slender structures (such as wind turbine or helicopter rotor blades) is therefore often idealised by 1-dimensional beams with associated cross sectional stiffness (and mass) properties, in which the beam strains are related to the applied forces via a 6×6 cross sectional stiffness matrix. Flexural-twist coupling is specified by the K₄₅ term from the cross sectional stiffness matrix. This paper clarifies the physical interpretation of K₄₅; describes an experimental technique used to derive the flap torsion coupling of composite beams, and compares experimental results with analytical and finite element predictions.