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Analysis of actuation and instabilities in dielectric elastomer devices

Liguori, Pietro 2023. Analysis of actuation and instabilities in dielectric elastomer devices. PhD Thesis, Cardiff University.
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Dielectric elastomer (DE) devices have gained significant interest in fields such as soft robotics, mechanical engineering, biomedical technology, and energy engineering due to their lightweight and fast actuation capabilities. However, these devices have several shortcomings that this thesis aims to address through the analysis of instabilities and actuation in various configurations. The electroelasticity theory is presented, defining the general kinematics and constitutive equations for these hyperelastic materials. Using this theory as a foundation, various configurations are introduced and analysed, with a focus on the novel ‘floating’ device as both a slab and tubular elastomer. These configurations are examined under different boundary conditions, and the deformation paths are analysed as geometrical parameters are varied. The onset of electro-mechanical instability is shown, as well as the introduction of the expansion limit. The theory of incremental deformations is specialised to investigate surface instabilities in three previously introduced elastomer slab configurations. It is shown that the instability is more sensitive to pre-stress in the ‘floating’ configuration, while the configuration deformed by sprayed charges is more stable against surface instabilities compared to the same configuration actuated by voltage. The effects of stiff electrodes on surface instabilities are also studied using surface-coating models, and it is demonstrated that the stability domain is significantly reduced when the device contracts. New bifurcation modes come into play and each one has been studied and characterised. Laminated composite elastomers are then considered, which are of particular interest due to their ability to enhance actuation characteristics. Using a small strain model and various boundary conditions, it is shown how, with specific parameters, an inverse mode of actuation can be achieved in both rank-1 and rank-2 laminated composites. The rank-2 laminate is demonstrated to enhance the rank-1 inverse actuation mode, and a guideline for optimizing composite parameters is provided. Existing materials are also analysed to show how current technology requires a rank-2 laminate to obtain the inverse mode of actuation.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Engineering
Uncontrolled Keywords: 1) Dielectric Elastomers 2) Surface Instabilities 3) Composite Elastomers 4) Electro elasticity 5) Small strain deformation 6) Laminated composites
Date of First Compliant Deposit: 4 July 2023
Last Modified: 04 Jul 2023 15:42

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