Effects of variable thickness and imperfection on nonlinear buckling of sigmoid-functionally graded cylindrical panels

The use of variable thickness can help the designers and researches reduce the weight of the functionally graded (FG) panel structures. For cases where reduction of weight is of high importance, such as space structures, ocean engineering, this type of panel is the best choice. Hence, this paper analyzes the effect of the variable thickness on nonlinear buckling of imperfect cylindrical panels made of sigmoid-functionally graded material (S-FGM) under combined axial compression and external pressure. The governing equations are in nonlinear form based on the classical shell theory with the von Karman assumption. By applying Galerkin procedure and the Airy stress function, the resulting equations are solved to obtain closed form expressions for critical buckling load and load-deflection curves. In numerical results, effect of variable thickness, the volume fraction index, imperfection size, loading as well as the geometric parameters on the load-dimensionless deflection curves are discussed in details.