This paper compares the performance of commercially available membranes made of styrenic rubber, natural rubber and acrylic elastomer for dielectric elastomer transducers operating in the large strain regime. Following a detailed description of the adopted experimental set-up and procedures, the results of a comprehensive electro-mechanical characterization of the three materials are reported to highlight the following dependencies: dielectric strength versus stretch, electrical conductivity versus electric field, dielectric constant versus stretch, stress versus stretch and strain rate. This includes the fitting of the experimental data with constitutive equations which provide material property values that can be used for model-based analysis, design and control of dielectric elastomer actuators and generators operating at large levels of strain amplitudes (like, for instance, transducer featuring actuation and generator strains over 100%) or in the presence of large pre-strains (over 100 %). Performance metrics relying on the identified constitutive parameters are introduced in order to discuss the specific pros and cons of the considered elastomers for the development of practical dielectric elastomer transducers.
Dielectric elastomer (DE) membrane transducers allow to achieve large strain, low energy consumption, low-noise, and highly compact mechatronic devices. To optimize the design of membrane DEs via numerically efficient software tools, as well as to develop accurate control and self-sensing algorithms, a lumped parameter model is required. In the case of rectangular DE strips clamped at both ends and subject to a uniaxial in-plane load, the resulting necking and inhomogeneous deformation turn out to be challenging to be described via standard lumped models, thus making it necessary to rely on numerically involved finite element (FE) tools. In this paper, we present a novel modeling framework that permits to accurately describe clamped DE membranes with generic aspect ratio in a control-oriented fashion. The model is grounded on an anisotropic free-energy function, which maps the inhomogeneities due to clamping within the constitutive membrane behavior. In this way, a lumped description of the DE can be obtained in terms of average stress and stretch quantities. After presenting the model, an extensive validation is performed by means of comparative studies with FE simulations as well as experimental results. It is observed how the proposed model permits to accurately describe the electro-mechanical response of clamped DE membranes for a wide range of aspect ratios, including nearly-uniaxial, nearly-pure shear, as well as intermediate configurations.
Dielectric Elastomer Transducers (DETs) are a promising technology for the development of actuators, generators and sensors with high performance and low cost. Practical application and economic viability of DETs is strongly affected by their reliability and lifetime, which depend on the maximum strain and electrical loads that are cyclically applied on such devices. To date, only limited information is available on the fatigue life performances of dielectric elastomer materials and of the transducers made thereof.This paper reports on a first lifetime constant electric-stress test campaign conducted on 38 free-expanding frame-stretched circular DET specimens, made of the silicone elastomer film Elastosil® 2030 250/150 by Wacker with blade-casted carbon-black silicone-elastomer electrodes, that have been subjected to nearly square wave electric field signals with 1 Hz frequency, 50% duty cycle and with amplitudes ranging from 65 MV/m to 80 MV/m.
Up to date, Dielectric Elastomer Actuators (DEA) have been mostly based on either silicone or acrylic elastomers, whereas the potential of DEAs based on inexpensive, wide-spread natural and synthetic rubbers has been scarcely investigated. In this paper, a DEA based on a styrene-based rubber is demonstrated for the first time. Using a Lozenge-Shaped DEA (LS-DEA) layout and following a design procedure previously proposed by the authors, we develop prototypes featuring nearly-zero mechanical stiffness, in spite of the large elastic modulus of styrenic rubber. Stiffness compensation is achieved by simply taking advantage of a biaxial pre-stretching of the rubber DE membrane, with no need for additional stiffness cancellation mechanical elements. In the paper, we present a characterization of the styrene rubber-based LS-DEA in different loading conditions (namely, isopotential, isometric, and isotonic), and we prove that actuation strokes of at least 18% the actuator side length can be achieved, thanks to the proposed stiffness-compensated design.
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