The Potential of Electroactive Polymers For Shape Shifting Structures

Abstract

Due to a global increase in energy consumption from an expanding population, research into ways to reduce energy use in buildings is increasing in importance. Proper daylighting strategies, when correctly integrated into building design, can have a major impact in the building energy balance. Proper daylighting can result in the decrease of artificial light energy use as well as lower heating due to solar radiation. In most structures, however, sun shading, an integral part of every building, still relies on ine cient shading methods and can be vastly improved. Alternate methods of sun shading employing adaptive structures can be used for improvement. This thesis explores how large strain characteristics of Dielectric Electroactive Polymers (Dielectric EAPs) could be exploited for adaptive shading structures through the experimental and numerical study of an elementary Dielectric Elastomer Minimum Energy Structure (DEMES). A DEMES is composed of a pre-stretched dielectric elastomer adhered to an inextensible compliant frame. In the DEMES studied in this thesis, the tension in the stretched membrane causes the frame to curl up, and when the structure is activated (voltage application), the frame returns to its initial planar state, forming a useful bending actuator. For the experimental study, a series of physical models were fabricated and successfully tested through a range of applied voltages. Experimental tests were also validated through a comparison with O'Brian et al. (2009). In addition, further investigation was conducted into the behavior of isotropically stretched DEMES. The isotropic behavior was identified to act similarly to different stretch ratios and produce similar effects. Physical models were also employed as a reference for the numerical study. For the numerical study, a modified dynamic relaxation algorithm was employed to model the DEMES. Dynamic relaxation is an iterative numerical method used to find a static equilibrium of a structure. The modified algorithm is an improvement upon existing dynamic relaxation formulations incorporating novel bending and clustering elements. It allowed for the study of key parameters such as the stiffness ratio between the frame and the membrane. Moreover, comparison with the physical models showed that the dynamic relaxation model correctly reflects the behavior of the studied DEMES. Finally, although the dynamic relaxation model is limited by approximated input values and mesh issues, the model is found suitable for future use in the design of adaptive DEMES shading systems.