Formulation and evaluation of an analytical model for composite box-beams

A direct analytical beam formulation is developed for predicting the effective elastic stiffneses and corresponding load deformation behavior of tailored composite box-beams. Deformation of the beam is described by extension, bending, torsion, transverse shearing, and torsion-related warping. Evaluation and validation of the analysis are conducted by correlation with both experimental results and detailed finite element solutions. The analysis is evaluated for thin-walled composite beams with no elastic coupling, designs with varying degrees of extension-torsion and bending-shear couplings, and designs with bending-torsion and extension-shear coupling. The analysis is performed well over a wide range of test cases, generally predicting beam deformations within 10 percent of detailed finite element solutions. The importance of three non-classical structural phenomena is systematically investigated for coupled composite beams. Torsion-related warping can substantially influence torsion and coupled torsion deformations; twist of a symmetric layup box-beam under a tip bending load can increase up to 200 percent due to warping. Couplings associated with transverse shear deformations can significantly alter the elastic response of tailored composite box-beams; effective bending stiffness of highly coupled anti-symmetric layup beams can be reduced more than 30 percent. Two-dimensional elasticity of the plies is also very important to the accuracy of composite box-beam analysis; load deflection results for anti-symmetric layup beams can be altered by 30-100 percent by not accounting for this elastic behavior.