Structural behavior of thin- and thick-walled composite blades with multicell sections

A mixed beam approach that combines both the stiffness and the flexibility formulation in a unified manner has been performed to model and analyze coupled composite blades with closed, multiple-celled cross sections. The analysis model includes the effects of elastic couplings, shell wall thickness, transverse shear deformation, torsion warping, and constrained warping. Reissner's semicomplementary energy functional is used to derive the beam force-displacement relations. The influence of the shell bending strain measures as well as the membrane strain measures are incorporated in the formulation. For completeness required in a rigorous beam theory, four separate continuity conditions are imposed on each cell of the closed, multicelled sections. The theory is validated against experimental test data, detailed finite element analysis results, and other analytical results found in the literature for coupled composite beams and blades with various cross sections. These include two-cell box beams with bending-torsion and/or extension-torsion couplings and bending-torsion coupled composite blades with two-cell airfoils. The correlation between the present theory and other methods is found to be good, dependent on the geometries and material distributions adopted in the blades. Numerical results showing the effects of including the shell bending strain measures are examined. The effects of inappropriate treatment of the direction of integration for two-celled composite beams are also investigated in the current framework of the analysis.