Buckling and vibration of composite folded-plate structures of finite length in combined shear and compression

Abstract

An accurate method is developed for analysing the critical buckling loads of folded-plate structures, notably longitudinally stiffened panels, of finite length, with diaphragm supported ends, when the component plates are loaded in combined biaxial compression and shear and the mode is of an overall type. The plates may be either isotropic or orthotropic; the latter are very nearly representative of most laminated fibre-reinforced composites. A Rayleigh-Ritz energy method is used, with the mode represented by a series of exact buckling modes of the structure subjected to the biaxial compressive loads alone. This results in a standard algebraic eigen-value problem, of order equal to the number of compression modes included in the series. A simple way of ranking the compression modes in order of relative importance is derived. The analysis has been incorporated into a general purpose computer program called casiopeia, which is capable of generating automatically any specified number of compression modes, and thence computing points on the interaction curve relating critical values of the compression and shear for any prismatic folded-plate structure of this type. Its efficiency is enhanced by providing a limited capability for assembling the structure from substructures. The program was applied to six stiffened panels that have previously been analysed by N. A. S. A. using an extremely expensive finite element method, and which provide the only accurate solutions available for comparison. The results were in close agreement. Finally it is explained how small modifications to the analysis enable natural frequencies of vibration to be obtained for folded-plate structures when the component plates carry combined compression and shear.