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Title: Mechanics of laminated bi-stable tubular structures
Author: Iqbal, K.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2002
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Bi-stable silt tubes made of laminated composites are novel deployable structures with two different stable configurations. In the first configuration the tubes are straight and strain-free. In the second configuration they are tightly rolled-up and subject to high levels of strain. To achieve this configuration, they have to climb up and across an energy barrier until a potential energy well is reached from where they can only jump out with some external help. These tubes can be used for large deployable structures as deployment actuators in a manner similar to a STEM. But, unlike the STEM, they do not need any drum to roll upon. The key to this bi-stable behaviour is a particular type of composite construction, invented by Daton-Lovett (1996), in which stiff fibres are arranged to ±α to the longitudinal axis, where α is about 45o. The fibre layout is anti-symmetric with respect to the mid-surface of the tube, to avoid twisting the tube when it is rolled up. Analytical models are presented to predict the radius of curvature in second stable configuration. These models assume linear-elastic behaviour of the material and derive the total strain energy expression, which includes the bending strain energy, membrane strain energy and coupled strain energy, within the tube. These models clearly show that the strain energy increases as we move away from the zero energy point, which corresponds to the extended, strain free configuration. This increase is particularly sensitive to the variations in the longitudinal curvature of the tube and less so to the variations in the transverse curvature. Another analytical model is presented to predict the edge deformations in coiled configuration using an anisotropic closed cylinder. It is shown that linear shell theory with appropriate adjustments works very well for laminated slit tubes.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available