General instability and face wrinkling of sandwich plates - Unified theory and applications.

The governing equations and applicable boundary conditions for sandwich plates with ideally orthotropic cores (honeycomb) are presented. The equations and boundary conditions are the first to be derived variationally with both transverse shear and normal strain effects included. The variational development, based on potential energy and the use of Lagrange multipliers to introduce face-core continuity requirements, leads to the desired results. It is noted that for symmetric buckling there are two multiple-choice boundary conditions per plate edge, and for antisymmetric buckling there are five multiple-choice boundary conditions per plate edge. The theory presented lends itself to certain exact solutions of the governing equations, where boundary conditions permit, and approximate solutions via the Rayleigh-Ritz procedure for more general problems. Buckling criteria are presented in the form of design charts, including both general instability and face wrinkling, for plates with one type of simple support, and for plates with one type of clamped loaded edges and simply supported unloaded edges. The ramifications of the present work relative to existing highly restricted solutions are examined and discussed.

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