If this era is ever named after a type of material, it may well become the era of smart materials. Compliant structures with integrated sensors and actuators reacting autonomously to changes in the environment via intelligent feedback control loops allow for entirely new solutions, e.g. in light-weight structures. A promising technology meeting the requirements for new actuator systems are the dielectric elastomers (DE). The simple working principle, inexpensive materials and unique features like the scalability, compliance, and light weight make this class of the electro-active polymers (EAP) attractive for many applications. The combination of large active deformations uni- or biaxially and the noiseless expansion, is unique among the available actuator technologies.
The present thesis is divided into three parts: The first part treats the subject of up-scaling planar membrane dielectric elastomer actuators. Designs for large-scale actuators were developed. The verification that the material scales after theory is provided from measurements on a planar agonist-antagonist test-rig. The strain and force difference at activation were predicted with existing material models and parameters and compared to the experimental results. The mechanical behaviour of the large-scale actuators can be predicted with classical non-linear continuum mechanics, considering viscoelasticity. Active deformation as well as blocking force scale with the dimensions of the actuator and with the number of layers respectively. Electrical properties, such as capacity and serial resistance of the electrodes were analysed and found to scale according to theory as well.
The specific material used as dielectric, VHB 4910, is well-known and characterized thoroughly. It has shown the largest active strain and the highest energy density of all the materials used so far in DE actuators. On the other hand it features several disadvantages, such as a high viscosity, and a limited range of temperature due to a high glass transition temperature. Therefore, in a second part of the thesis, two other materials, introduced more recently, were evaluated. The first material consists of pre-stretched VHB 4910 that is modified with an interpenetrating TMPTMA network, resulting in a composite material of two intermingled elastomers, one under tension and one under compression. The second material is a silicone with corrugated silver electrodes. The three materials were characterized under comparable testing conditions and their performance as actuators was evaluated in an isotonic activation test and on an agonist-antagonist hinge configuration.
In the third part, a proof-of-concept for the large-scale VHB 4910 actuators was done on a biomimetic airship with fish-like propulsion. The airship is propelled by the interaction of a wave motion pattern of the body and caudal fin, resulting in a Karman-type vortex street in the wake of the airship. Bending the helium-inflated body and a caudal fin is realized with large planar DE actuators in agonist-antagonist configurations. The focus of the design process was on the DE actuators as artificial muscles. In a first flight test, the transfer of the fish-like movement from water to air was verified. Valuable experimental experience was gathered concerning large-scale DE actuators, which can be used for future large-scale structures in active and adaptive systems.