Effect of elliptical cutouts on buckling and vibration characteristics of stiffened composite panels under non-uniform edge loads

This study is motivated by the need to understand the effect of elliptical cutouts on the buckling and vibration characteristics of stiffened composite panels under the influence of various types of non-uniform in-plane edge loads. The study is carried out by using a Finite Element (FE) formulation wherein the plate, and the stiffener are discretized by employing a 9-noded heterosis plate element and a 3-noded isoparametric beam element, respectively. The contributions of shear deformation and rotary inertia are considered in the FE formulation. Since the stress distribution within the panel is highly non-uniform for a given loading and geometric imperfection, a dynamic approach has been adopted to solve the buckling problem wherein two sets of boundary conditions are used to calculate the pre-buckling stresses and the buckling load of the stiffened panel. A new structured mesh pattern is proposed to house the stiffeners attached to the centrally located elliptical cutout panel in the form of a grid so that the stiffener can be attached anywhere and in any direction as per the requirements. The influences of various parameters, such as ply orientation, cutout size, cutout orientation, boundary conditions and depth to width ratio of the stiffener, are examined in detail. From the analysis, it is noticed that the depth of the stiffener has a significant effect on the buckling and vibration characteristics of the panel.