Formulation and Evaluation of an Analytical Model for Composite Box‐Beams

A direct analytical beam formulation is developed for predicting the effective elastic stiffnesses 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 exprimental 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.