Theoretical and Experimental Investigation of the Nonlinear Behavior of Composite Beams

As part of the research on the aeroelasticity of helicopter blades, a nonlinear kinematic model has been developed for an initially twisted composite beam. The beam undergoes large rotations but small strains. Some non-classical effects such as transverse shear deformations and elastic couplings that arise from the anisotropic behavior of composite materials are included in the formulation. The effects of differential warping, such as that which arises when warping is constrained, are ignored; whereas warping effects, both in- and out-of-plane are retained. A finite element program has been developed on the basis of the theoretical model. This can predict static behavior as well as calculate natural frequencies and mode shapes of a rotating beam subjected to external loads. The sectional stiffnesses required for the calculations are determined using an extension of NABSA which is a two-dimensional finite element program. For validation of both the theoretical model and numerical code, calculations are compared with experimental data from published work and from the present investigation on a non-uniform torsionally soft model blade. Parametric studies are also carried out to show transverse shear effects