Abstract. Thin-walled composite shells are used as main structural components in various branches of engineering. Buckling is the key design criterion for these ...
Buckling Load Estimates for Composite Cylindrical Shells Based on Koiter’s Initial-Postbuckling Theory Using Representative Imperfection Patterns Eelco Jansen1, Tanvir Rahman2, Raimund Rolfes1 1
Leibniz Universitaet Hannover, Institute of Structural Analysis, Appelstrasse 9A, 30167 Hannover, Germany 2 TNO DIANA BV, Delftechpark 19a, 2624 XJ Delft, the Netherlands
Abstract Thin-walled composite shells are used as main structural components in various branches of engineering. Buckling is the key design criterion for these thin-walled structures. Cylindrical shells typically exhibit unstable post-buckling behavior and their behavior is correspondingly very sensitive to small geometric or load imperfections. In recent years extensive research has been carried out in order to develop design approaches that lead to appropriate, not overly conservative, design loads, e.g. [1]. A deterministic approach to define knockdown factors in the design of cylindrical shells is based on Koiter’s initial post-buckling theory. Initial post-buckling analysis provides a well-established framework to obtain buckling load estimates for imperfection sensitive structures. In the literature, Koiter’s approach has often been used with a limited number of buckling modes using a small set of affine or for other reasons relevant imperfection modes. In earlier work of the present authors, a multi-mode finite element implementation of Koiter’s theory, including a nonlinear prebuckling state, was presented, and the capability to predict the limit-point buckling load of a specific composite cylindrical shell for a small set of buckling modes and corresponding imperfection modes was shown [2]. The multi-mode capability provides the possibility to use representative imperfection patterns in the analysis. In the present contribution, two approaches to obtain buckling load estimates are presented. In the first approach, a realistic (e.g. measured) imperfection pattern is decomposed in the vector space spanned by the buckling modes. Alternatively, for a given appropriate set of buckling modes and corresponding imperfection modes, the amplitudes of the imperfection modes are chosen such, that the most imperfection sensitive case for this given set is considered. The two approaches can be used as the basis of a design procedure accounting for the degrading effect of geometric imperfections and they are illustrated for specific, characteristic cases of composite cylindrical shells under axial loading. References [1] W.T. Haynie and M.W. Hilburger (2012), Comparison of methods to predict lower
bound buckling loads of cylinders under axial compression. In Proceedings of 51st AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference, Orlando, Florida, pages 1–10. [2] T. Rahman and E.L. Jansen (2010), Finite element based coupled mode initial postbuckling analysis of a composite cylindrical shell. Thin-Walled Structures, 25, 1939– 1946.
