Nonlinear analysis of anisotropic plates with initial imperfections and various boundary conditions subjected to combined biaxial compression and shear loads

The postbuckling behaviour of anisotropic panels with initial imperfections is investigated. Nonlinear analysis is developed for symmetric panels under combined biaxial compression and shear loads in order to obtain the out-of-plane panel deflection in the postbuckling range. The nonlinear differential equations are obtained by using the principle of the stationary value of the total potential energy and 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. The theoretical results are in good agreement with the few results concerning isotropic plates and the simply supported anisotropic results found in literature. A new and original test facility was built in order to apply simultaneously both biaxial compression and shear loads. An anisotropic panel, clamped along the four edges, has been tested under different combined loads; the correlation between the experimental and analytical results has been quite good. The results demonstrate the influence of initial imperfections on panel deflection in the postbuckling range: the curves obtained experimentally in the presence of imperfections cross those obtained theoretically, where imperfections are ignored (producing lower out-of-plane deflection).