Free-standing tubular DEAs for multi-directional bending

Highly anisotropic, fiber-based structures are a successful concept in nature. Usual dielectric elastomer actuators are entirely soft and rely on the integration of stiff carrier frames for the fragile dielectric membranes. Within this work, a completely soft, fiber-reinforced free-standing tubular actuator concept is presented. The circumferentially running carbon fibers are integrated into the inner electrode of the DEA and stabilize the cross-section, while having negligible impact on the mechanical stiffness in the axial direction. Through the segmentation of the outer electrode of the actuator, active bending in the corresponding directions is achieved. Moreover, if all segments are activated simultaneously, the actuator expands axially. The presented manufacturing approach allows for the adjustment of the dimensions over a wide range of diameters and lengths. Furthermore, the local stiffness of actuators can be tailored by varying the amount of fibers incorporated into the electrode. The electroactive deformation of actuators with different diameter-to-length ratios and fiber densities is investigated.