On nonlinear thermo-electro-mechanics in the context of electro-active polymers

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The ever increasing demand for functional materials while simultaneously assuring low production costs has led to a strong focus on smart materials in the past two decades. Prominent examples of this class of materials are electro-active polymers that can change their form and mechanical properties due to external stimulation by an applied electric field.As a result of the high electric voltages that are needed to induce the electric field but also due to other external influences during the application of electro-active polymers, significant changes in the temperature of the material may occur. Therefore it is crucial to consider these thermal influences on the material behavior as well. Thus in the first phase of this project the basics of the coupled thermo-electro-mechanical problem were developed and solved using both analytical and numerical methods.In the second phase of this project we initially aim to conduct experimental investigations on various (rate-dependent) electro-active materials. To this end we will extend the testing equipment that is available at the Chair of Applied Mechanics of the University Erlangen-Nuremberg. The results of these tests will be used to validate the theoretical framework that was developed in the first phase of this project. In the experiments two types of electro-active materials will be tested. We will use the commercially available material VHB 4910 and a silicone, filled with piezoactive particles, that is custom made and provided for our experiments by the Chair of Polymeric Materials at the University Erlangen-Nuremberg.Subsequently the validated numerical implementation will be used to analyze the influence of a number of internal and external effects on the material. We will investigate for example how the free space surrounding a material sample influences the results of the numerical simulation. Furthermore the role of the microstructure of the material will be investigated in more detail. For this we will introduce two different scales on which the material is observed. This will include the microscale where the exact microscopic structure of the material is depicted and the macroscale where the material is considered to be homogeneous. The formulation of a scale transition between the micro- and the macroscale will eventually lead to a more realistic description of the material behavior. This is especially important for materials for which the internal structure cannot be considered to be homogeneous. This is for example the case for the particle filled silicone composite used in the experiments. Finally a novel formulation for the driving forces at defects in the material will be established. Thereby, with respect to electro-active polymers, the piezoactive particles in the silicone composite can be considered as such defects.