A study of the buckling behavior of stiffened composite shells
Moradi, Behrooz
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Permalink
https://hdl.handle.net/2142/21624
Description
Title
A study of the buckling behavior of stiffened composite shells
Author(s)
Moradi, Behrooz
Issue Date
1992
Doctoral Committee Chair(s)
Parsons, I. Dennis
Department of Study
Civil and Environmental Engineering
Discipline
Civil Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Civil
Language
eng
Abstract
Studies are reported that examine the buckling behavior of stiffened composite shells. First, dimensional analysis is applied to a simple model of stiffened laminated cylindrical shells to determine the dimensionless parameters that characterize the buckling of these structures. Donnell shell theory is used to describe the kinematic deformation of the shells. The axial and ring stiffeners are modeled using the smeared technique. A nondimensional load is defined as a function of nine nondimensional parameters which are a combination of the material and geometric properties of the shell. Additional assumptions regarding the construction of the shell walls can be used to reduce the number of nondimensional parameters. Some simply-supported shells subjected to hydrostatic pressure are examined to demonstrate the use of the dimensionless parameters. Estimates of the imperfection sensitivity of these shells are made using Koiter's asymptotic theory. The dimensional analysis provides a framework for the systematic investigation of the effect changes in material and geometry have on the buckling loads of stiffened composite shells. The results of this analysis are intended to provide information that can be used in the preliminary stages of a shell design.
Second, an investigation is made into the accuracy of different methods that are commonly used to numerically compute the buckling loads of stiffened shells. Three different methods are employed to estimate the buckling loads of several ring stiffened cylindrical shells and shells made of orthotropic material. These methods are a nonlinear bifurcation analysis and two linearized buckling analyses, one that ignores the initial displacement stiffness matrix, and one that includes it. Large differences are observed between the predictions made by the two linearized buckling analyses for a range of shell geometries. Detailed studies of a shell with six ring stiffeners demonstrate that these differences are caused by the different versions of the linearized eigenvalue problem, rather than by the use of different numerical formulations. Investigations of the prebuckling behavior of this cylinder show that significant nonlinear deformations occur. This means that a nonlinear bifurcation analysis must be used to accurately estimate the buckling load of this geometrically perfect shell.
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