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2.3 MECHANICAL ENGINEERING
Dielectric elastomers (DEs) possess many useful properties including the capability of achieving large deformation, quietness of operation, high energy density and coupling efficiency. However, DEs generally require very high actuation electric field strength (> 100 V/μm) which can limit their useful lives. A DE with low Young‟s modulus, large elongation at break and high dielectric constant has the ability to exhibit high deformation under a relatively low electric field. Much research has been conducted to overcome the need for high actuation electric fields. One popular approach to achieve this goal is to fabricate silicone rubber (SR) based DE composites combined with high dielectric fillers. The primary aim of this work was to design and fabricate DEs which exhibited the capability of large voltage-induced deformations at relatively low electric field strengths whilst eliminating electromechanical instability (EMI) though the application of equi-biaxial pre-stretching. Barium titanate (BT) possessing a high dielectric constant, was chosen as the filler to enhance the overall dielectric constant of SR based DEs. The morphological features of all materials used in this work were observed using a Scanning Electron Microscope (SEM). The elemental analysis of these particles was carried out using an Energy Dispersive X-Ray Spectrometer (EDS) which was coupled to the SEM and Fourier Transform Infrared Spectroscopy (FTIR). Dielectric measurements of DE films were conducted on a Turnkey broadband dielectric spectrometer. Their equi-biaxial mechanical properties were studied using a bubble inflation test method.
It was found that SR/BT films exhibited large actuated strains of 57% after being subjected to equi-biaxial pre-stretch ratios which coincided with the minimum secant moduli of the test samples. Using a coating method to modify BT particles with dopamine (DP) not only enhanced the compatibility between the SR and the particles, but also tuned the cross-link density of the SR matrices. One of the resulting DE films of SR/20 wt% DP-BT, possessed a dielectric constant of 7.5, a Young‟s modulus of 0.2 MPa and achieved a large voltage induced strain of approximately 80% at a relatively low electric field strength of 53 V/μm when pre-stretched to a ratio of 1.6. Moreover, it was found that the occurrence of EMI in the SR/20 wt% DP-BT composite was eliminated by applying equi-biaxial pre-stretch ratios above 1.6. By comparison, the EMI in a commercial DE, 1 mm thick acrylate film, VHB 4910, was eliminated by equi-biaxially pre-stretching to a ratio above 2.0.
It is recommended that future work should focus on the dynamic performance of an SR/DP-BT DE fabricated in-house when subject to an electric field. Further, fatigue life of the material should be investigated both with and without the application of an electric field. Thereafter, an approach to fabricating DEs having the capability of achieving large voltage-induced strains without the requirement for equi-biaxially pre-stretching is also proposed in order to prolong test sample and component life. Finally, an application for the novel DE material, a rotary motor, is proposed. An in-house designed and fabricated DE with suitably tailored electromechanical properties will be used.
Jiang, L. (2016) Design and development of dielectric elastomers and elimination of electromechanical instability under equi-biaxial loading.Doctoral Thesis, Technological University Dublin. doi:10.21427/D7J88Z