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Title: Time-dependent bistable morphing structures
Author: Brinkmeyer, Alex
ISNI:       0000 0004 5349 9140
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2014
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An investigation into the time-dependent effects of bistable morphing and deployable structures is presented, showing how the stability of these structures is influenced by viscoelastic effects and how these effects can be used as an advantage to engineer novel morphing concepts. In the context of space applications, significant relaxation effects appear in structures that have been stored for a long duration, e.g. in a space vehicle prior to launch. Here, the deployment of an ultra-thin CFRP tape spring is first studied, with the aim of understanding how long-duration stowage causes changes in its stability and how it affects its deployment behaviour. Analytical modelling and experiments show that the deployment time increases predictably with stowage time and temperature, and that analytical predictions compare well with experiments. For cases where stress relaxation become high, the structure is shown to lose its ability to deploy autonomously. Next , structures that exhibit a time-dependent effect called pseudo-bistability are considered. A pseudo-bistable structure is one that is able to gain a new stable state during relaxation and therefore becomes temporarily bist able. This is exploited to yield a novel structure which, once actuated to its second stable state, can return dynamically to its initial state after a certain recovery time without further actuation. The concept of pseudo-bistability is first demonstrated using an analytical spring-and-dashpot model, then is studied in an isotropic spherical dome through numerical modelling and experimental validation. It is shown, in particular, that a well-known geometrical parameter can be used to correlate the geometry of the dome to its recovery time. The pseudo-bistable effect is then demonstrated in a prestressed panel, and the use of composite reinforcement is considered to improve the stiffness of the structure. Results show that a limiting volume fraction exists at which the pseudo-bistable behaviour is lost. Finally, an application is proposed, whereby a pseudo-bist able structure acts as a flow controller in an air duct. Using a fluid- structure simulation, fluctuations in the outlet pressure are shown to be selectively damped by the pseudo-bistable device. In the last chapter, various other conceptual applications using time-dependent bistable devices are also explored, in the hope that this work is taken further.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available