Buckling of Discretely Stringer-Stiffened Composite Cylindrical Shells under Combined Axial Compression and External Pressure

In this paper, the static buckling of especially orthotropic stringer-stiffened composite cylindrical shells subjected to combined axial compression and external pressure is investigated, based on geometrical non-linear analysis with considering pre-buckling deformations. The kinematic relation of shells is based on the Donnell non-linear theory and First Order Shear Deformation (FOSD) is adopted for both shell and stiffeners. Displacements, rotations and interacting forces are expressed in terms of Fourier series expansions as independent approximate solution functions. Unknown coefficients of shell and stringers are related by satisfying continuity conditions of displacements at their contact areas using Lagrange multipliers. The non-linear equilibrium equations are obtained using the Ritz method. The effects of sensitivity parameters, e.g., shell lay-ups, different numbers of stringers in the circumference, location of stiffeners (outside vs. inside) and the discrete versus smeared approach on interaction buckling curves are considered. Results indicate remarkable differences between outside and inside stringer-stiffened cylinder buckling loads and also illustrate the fundamental role of shell stacking sequences and stiffened shell geometry on the applicability range of the smeared stiffener approach.