There is an increasing interest to use novel elastomers with inherent or modified advanced dielectric and mechanical properties, as components of dielectric elastomer actuators (DEA). This requires corresponding techniques to assess their electromechanical performance. One performance criterion is the electrically induced deformation of the active electrode area. In this work, a rectangular DEA is used to investigate the influence of the ratio between the active electrode and the passive area on the actuator deformation. For this purpose, a dielectric silicone film is bonded on one surface to a unidirectional carbon fiber fabric. Thereby, highly anisotropic mechanical properties are implemented. When strains are applied perpendicular to the fiber direction, the composite hardly contracts in the fiber direction due to the superior stiffness of the fibers. In addition, the conductive fiber structure also acts as a highly anisotropic compliant electrode. By application of a second paste-like electrode onto the silicone film a DEA is created that operates in a pure shear configuration. This assembly enables the modification of the active-to-passive area ratio and the investigation of its effect on the actuator deformation. Image-based measurements are used to determine the strain of the active electrode area. The experimental results are compared to a lumped-parameter model that considers the electromechanical properties of the fiber-reinforced DEA. In summary, the ratio of the active-to-passive area has a significant influence on the measured deformation. Especially for novel actuator materials that do not exhibit large strains, an active-to-passive ratio of 50 % proves to be particularly advantageous.

Dielectric elastomer actuators (DEAs) have advantageous characteristics and, therefore, their application is widespread in the field of soft robotics. Their properties can be specifically adapted by both the selection of materials and the manufacturing process. Previous research has shown that fiber reinforcement of the structure can significantly enhance the unidirectional motion. In the presented work an actuator consisting of a silicone film as the dielectric, a textile carbon-fiber-reinforced electrode and a carbon black electrode are used. The electrode based on the carbon fibers additionally serves as unidirectional stiffener. Due to this highly anisotropic textile electrode, the DEA barely contracts in fiber direction. However, the active force of the DEA during actuation can be further increased through an initial pre-stretching. The aim of this work is to investigate the influence of the pre-stretching in fiber direction on the actuator performance and the long-term stability of the pre-stretch. The active force of different actuators is recorded with uniaxial tensile tests over several deformation cycles. This enables the investigation of effects deriving both from the manufacturing process and the layer structure of the textile DEA. The acquired data are evaluated and compared to results of an analytical model. To explore the ability of the fibers to maintain the initial pre-stretching of the DEA during activation, digital image correlation as an in-situ imaging technique is applied. It could be shown shown that there is no change in width due to the anisotropy. The results of the investigations are used to control and improve the manufacturing process of the textile DEA.

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