Nonlinear analysis of graphite epoxy/wing boxes under pure bending including lateral pressure

Abstract

Additional loads are created on wing-box panels when bending loads are applied to the box beam. Bending curvature, associated with longitudinal load, causes a distributed load perpendicular to both upper and lower wing-box panels resulting in a lateral pressure. The nonlinear analysis of anisotropic panels with initial imperfections has been developed for symmetric panels under combined biaxial compression, shear loads, and lateral pressure in order to obtain the out-of-plane panel deflection in the pre- and postbuckling range. The nonlinear differential equations are expressed in terms of the out-of-plane displacement and the Airy function. They are solved with the Galerkin method for various boundary conditions. Only by taking into account the nonlinear effects of the lateral pressure on the skin panels is it possible to obtain a good correlation between theoretical and experimental behavior. Experimental results on graphite/epoxy wing-box beams under pure bending showed remarkable deformations of the panels (particularly the compressed panel) in a direction normal to their centroidal surface, affecting both local strain values and the failure load value of the structures. Due to the effect of the lateral pressure, the blade-stiffened panel wing box showed a remarkable deformation also in the prebuckling Held.