The postbuckling behavior of stringer-stiffened composite cylindrical panels is studied analytically and experimentally. Progressive failure analysis is implemented for the prediction of failure characteristics and postbuckling ultimate load. For the progressive failure analysis, the maximum stress criterion is applied to the average stress in each layer of all the finite elements. The present study utilizes the formulation of geometrically nonlinear finite element procedure based on the updated Lagrangian description with the second Piola-Kirchhoff stress tensor and the Green strain tensor, and the eight node degeneated shell element for finite element for finite element modeling of the laminated shell structure. In modeling stringers, new scheme to analyze the global and the local buckling of the stiffened panel is introduced. Results of the nonlinear finite element method combined with the progressive failure scheme is compared with experimental results. Present finite element results with considering of progressive failure scheme shows good agreement with experiment in the buckling load, postbuckling ultimate load, failure and deformations. As the numerical examples, the postbuckling behavior of stringer-stiffened composite panels under compression is investigated from the initial load, through the buckling and to the final collapse. The buckling load tends to be affected by the bending stiffness in axial direction, but the postbuckling ultimate load has nothing to do with it. The location of Blade-type stringer does not affect the buckling load and the postbuckling ultimate load nearly. The panels with Blade-type stringer shows many shear failure on skin and stringer near the intersection of skin and stringer. The panels with Wide Flange-type stringer shows many shear failure on skin and stringer near the intersection of skin and web, and the intersection of web and flange. Shear failure concentrated on the side stringer by large deformation disables the panels from carrying additional loads, and the structure collapses immediately.
