|Ph.D Student||Goshkoderia Artemii|
|Subject||Multiscale Instabilities in Active Elastomers|
|Department||Department of Aerospace Engineering||Supervisors||Professor Itzchak Frankel|
|Dr. Stephan Rudykh|
|Full Thesis text|
This thesis presents a study of coupled magneto- and electro-mechanical behavior and instabilities of soft active materials. I specifically focus on electro- and magneto-mechanical instabilities in microstructured dielectric and magnetorheological elastomers (DEs and MREs, respectively) undergoing large deformations. The macroscopic or long-wave instabilities analysis is implemented into finite element code and stable and unstable domains of DE and MRE composites are identified. It is shown that the magnetic field can induce dramatic microstructural transformations in MREs with chain-like microstructures at the microscopic level.
(i) Macroscopic instabilities in dielectric elastomers: I examined the role of microstructure geometrical parameters and material properties on the stability of the DE composites. It is found that the unstable domains can be significantly tuned by an electric field, depending on the electric field direction relative to pre-stretch and microstructure. More specifically, the electric field aligned with the stretch direction, promotes instabilities in the composites, and the electric field applied perpendicularly to the stretch direction, stabilizes the composites. I showed that contrasts in relative permittivity constants and shear moduli of the phases dramatically affects the stability of dielectric elastomers.
(ii) Macroscopic instabilities in magnetorheological elastomers: The effect of microstructure and material parameters on the stability of MRE composites with circular and elliptical particles is studied. The isotropic Langevin model for magnetic behavior, to account for the initial (linear) susceptibility and saturation magnetization of the magnetoactive inclusions is used. I analyzed the influence of the applied magnetic field and finite strains, as well as particle shape and material properties, on the stability of the MRE composites. It is found that the stable and unstable domains can be significantly tuned by the applied magnetic field, depending on deformation, microstructure and magnetic properties of the inclusions such as initial susceptibility and saturation magnetization.
(iii) Instability-induced microstructural transformations: Instability-induced pattern formations in soft MRE composites with chain-like microstructures are investigated. It is shown that identical MRE composites with periodically distributed particles can switch to a variety of new patterns with different periodicity upon developments of instabilities. The newly formed patterns and post-buckling behavior of the MAEs are dictated by the magnitude of the applied magnetic field. The particular levels of magnetic fields that give rise to strictly doubled, or multiplied periodicity upon onset of instabilities in the periodic particulate soft MAE are identified.
This thesis provides the foundation for predicting instabilities in soft active composites. The findings can be useful in further design of active materials with enhanced properties, switchable functionalities, or tunable material microstructures remotely controlled by the external stimuli.