Global and local buckling analysis of grid-stiffened composite panels

There is a renewed interest in grid-stiffened composite structures; they are not only competitive with conventional stiffened constructions and sandwich shells in terms of weight but also enjoy superior damage tolerance properties. In this paper, both global and local buckling is investigated for orthogrid- and isogrid-stiffened composite panels. Homogenized properties corresponding to classical lamination theory are obtained by matching the strain energy of stiffened and equivalent unstiffened cells, and then used in global buckling analysis. Bloch wave theory is adopted to calculate the local buckling load, where the interaction of adjacent cells is fully taken into account. Instead of considering skin buckling and stiffener crippling separately, the skin and stiffeners are assembled together at the level of a characteristic cell. The critical instabilities can be captured whether they are related to the skin, stiffener or their interaction. The proposed combination of global/local models can also be used to predict the material failure. Numerical examples of isotropic panels show that the local buckling loads predicted by the proposed method match detailed finite element calculations well for eccentric or symmetrically located stiffeners with different torsional stiffness. The proposed method is further validated using typical composite configurations of flat panels and circular cylinders.