Anisotropic Stiffened Panel Buckling and Bending Analyses Using Rayleigh–Ritz Method

Abstract

A Rayleigh–Ritz energy method application is proposed to calculate the buckling onset and bending behavior of flat rectangular anisotropic composite stiffened panels submitted to any combination of in-plane loads (biaxial compression and shear) and pressure. Panels may consist in any kind of anisotropic laminate. Thickness, lay-up and material property changes are allowed along both longitudinal and transverse directions and transverse shear effects are considered using a first order theory. Stiffeners, idealized as offset beams, can also be placed in both directions. Simply supported edges are the assumed boundary conditions for the panel. Nevertheless, additional restrictions can be added by means of the definition of certain torsional or flexural stiffness at the edges. Therefore, clamped conditions or any other condition between clamped and simply supported can be analyzed. The consideration of all these features, together with the potentially high computational performances of the Rayleigh–Ritz method compared with the classical finite elements analyses, enables a wide application in real aircraft structures, such as CFRP (composite fiber reinforced plastic) torque box covers and spars with elevated performances and accuracy. Comparisons with finite element methods and tests in real structures are shown.