STABILITY OF COMPOSITE AND SANDWICH STRUTS BY MIXED FORMULATION

A unified mixed, higher-order analytical formulation is presented to evaluate the buckling of laminated composite struts. The formulation can also be used to evaluate the overall buckling and wrinkling loads of a general multilayer, multicore sandwich strut having any arbitrary sequence of stiff layers and cores. The usual assumptions of thin stiff layers and antiplane core are advantageously eliminated. Displacements as well as transverse stress continuities are enforced in the formulation by incorporating them as the degrees of freedom, thus avoiding separate calculations of the modal transverse stresses. Two sets of mixed models are proposed, based on individual layer and equivalent single layer theories, by selectively incorporating nonlinear components of Green's strain tensor. Limitations of the equivalent single-layer theories and typical simplifying assumptions are highlighted. A parametric investigation is presented, concerning the influence of the material and geometric properties on the buckling behavior of a sandwich strut. A few recommendations are also made for the stability analysis of laminated composite struts.