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Title: Post-buckling of variable-stiffness shell structures
Author: White, Simon C.
ISNI:       0000 0004 5993 6794
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2016
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The cylindrical shell is one of the most efficient structures for resisting axial compression. They are found in many weight-critical engineering applications due to their low mass and large internal volume. Their structural efficiency is derived from surface curvature which results in large buckling loads. Ultimate failure is generally due to local buckling (i.e. loss of stability of the shellwall) which is followed by global collapse. A consequence of this unstable non-linear behaviour is that the structures are sensitive to imperfections and buckle at loads that are a fraction of their linear buckling eigenvalues. In contrast, flat structures (such as plates and stiffened panels) display a relatively well-behaved post-buckling response. In this thesis an investigation into the post-buckling behaviour of variable-stiffness shell structures is presented. Its aim is to determine whether or not cylindrical shells can be designed to have stable post-buckling configurations by adopting non-uniform material properties. In order to create shells with new and novel responses, the design space must be expanded by removing the standard rules for laminate design. Therefore, the present work focuses on laminates in which the reinforcement fibres are not straight but follow curvilinear paths. Such structures are termed variable-stiffness composite structures, due to their smooth variations in anisotropy (i.e. their section stiffnesses and kinematic coupling). Cylinders, curved panels and flat plates are tailored for improved post-buckling performance using numerical methods. In the case of cylindrical shells, dynamic analyses are performed in order to capture the effects of instability, inertia and path switching. Here, tailoring was performed on cylinders with a circumferential fibre-angle variation in a parametric study. The results show that a wide range of responses can be achieved by varying the shell's geometry and fibre-angle distribution. New evidence is presented that cylinders with stable post-buckling responses are possible by using variable-stiffness laminates. Tailoring is also performed on curved panels through an optimisation process. Panels .are modelled using Koiter's asymptotic method and a quadrature-based discretisation of the domain. Optimisation is performed using a genetic algorithm with the objective of increasing the structure's tangent stiffness in the vicinity of the bifurcation. An optimised shell design is presented which is practically unaffected by the increase in radial displacements in terms of axial stiffness.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available