Thursday, April 5, 2012
Mechanical and Civil Engineering Seminar
Controlling Adaptive Materials and Structures with Electrons and Photons
William Oates, Assistant Professor, Department of Mechanical Engineering, Florida State University
Research in adaptive materials and structures has seen exponential growth in the past couple of decades due to interest in multi-functional materials and bio-inspired structures. In this talk, the material and structural behavior of electroactive dielectric elastomers will be compared to photomechanical liquid crystal polymer networks. First, it will be demonstrated how dielectric elastomers provide unique capabilities for controlling flow in low Reynolds number environments. Up to 20% lift enhancement on a small scale (micro air vehicle) wing has been achieved by applying an electric field to the dielectric elastomer membrane wing. Furthermore, lift can be recovered poststall by applying a field. Wind tunnel experiments conducted at the Air Force Research Laboratory at Eglin Air Force Base will be presented. While dielectric elastomers have achieved success in this application and others such as robotic manipulators, they require electrodes and on-board power supplies to deform the material with an applied voltage. In contrast, a relatively new class of glassy polymers functionalized with azobenzene liquid crystals has been under investigation. This class of materials convert light directly into mechanical work. Blue-green polarized light induces a complex photon induced molecular structure change (photoisomer- ization) which leads to macroscopic deformation of the host polymer network. This provides a unique capability for spatial and temporal control of smart materials that can be directly controlled with a laser or light emitting diode (LED). A comparison of the performance of these materials will be given using nonlinear continuum mechanics, phase field microstructure modeling, and coupling with electromagnetics of light waves. Comparisons with experiments will also be given to illustrate important photomechanical molecular coupling to the host polymer network.