A new higher-order laminate theory is developed for delamination buckling and postbuckling analysis of composite plates and cylindrical shells. The refined displacement field, proposed in the theory, accounts for transverse shear effects through the thickness of the laminate. It is capable of representing displacement discontinuity conditions at the delamination interface and the separation and slipping conditions between the delaminated layer and the sublaminate. It also satisfies the traction-free boundary conditions at all free surfaces including the delamination interface. Delaminated composite plates and shells with various material properties, thicknesses, ply angles and stacking sequences are analyzed. The results show significant transverse shear effects and indicate that delamination plays an important role in the buckling and postbuckling modes thereby governing the failure mechanism. The results of the theory correlate very well with experimental data. The present theory provides an adequate framework for analysis of delaminated composite elements with arbitrary thicknesses.; In addition to the new higher-order theory, both two- and three-dimensional elasticity solutions are developed for buckling of simply supported composite plates. The uniform stress assumption is made for the prebuckling state of laminates. The goal is to use these solutions to assess the accuracy of the existing approximate theories. The two-dimensional elasticity solution procedure is also extended to model delamination buckling of composites. The elasticity solutions accurately account for the transverse shear and the transverse normal deformations which are critical for thick composites. The elasticity-based approach is then used to validate the various plate theories including the developed new higher-order theory. The higher-order theory shows good agreement with the elasticity solution for moderately thick composites while the classical laminate theory performs poorly.; Finally experimental investigations are performed to validation the analytical models. Compression tests are conducted on clamped flat composite specimens with pre-existing delaminations. All test specimens are fabricated using graphite/epoxy material. Delaminations of various sizes and locations are introduced by double sheets of Teflon strips placed at the ply interface through the width. The experimental results validate the new higher-order theory in both delamination buckling and postbuckling analysis.
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