Torsional buckling analysis of composite cylinders

A buckling analysis of composite cylinders under torsion is performed by us ing the geometrically nonlinear finite element analysis. A nine-node assume d strain shell-element model with six degrees of freedom per node is used f or the analysis. The buckling load of a composite cylinder is found by sear ching for a bifurcation point on the geometrically nonlinear deformation pa th. The corresponding buckling mode is obtained from the eigenvalue analysi s at the bifurcation point. Numerical results show good agreement with line ar solutions for isotropic and most composite cylinders, but large discrepa ncies in some cases. This discussion focuses on the pinpoint of the bifurca tion point on the nonlinear path and the differences of torsional buckling loads between the nonlinear and linear solutions for various types of compo site cylinders.