Wave propagation, instabilities, and pattern transformation in dielectric elastomer composites: Application to tunable soft phononic crystalsJandron, Michael AnthonycreatorHenann, DavidAdvisorBower, AllanReaderSrivastava, VikasReaderBelden, JesseReaderBrown University. Engineering: Mechanics of Solidssponsor201924, 140 p.born digitalThesis (Ph. D.)--Brown University, 2019thesesPhononic crystals are periodic, composite solids that exhibit phononic band gaps – frequency ranges in which elastic waves are prohibited. When made from soft elastomers, phononic band gaps may be reversibly manipulated through large elastic deformation of the periodic structure. By using dielectric elastomers, which undergo large, reversible deformations when subjected to an applied electric field, the frequency ranges of band gaps may be adjusted, and new band gaps may be created. This thesis addresses several problems related to the tunability of phononic crystals comprised of dielectric elastomer composites. First, we present our finite-element-based numerical simulation capability for designing electrically-tunable, soft phononic crystals. Our finite-element tools address both nonlinear quasi-electrostatic processes and the linearized dynamics of electroelastic wave propagation through a pre-deformed state and may be applied to general composite unit-cell geometries subjected to arbitrary far-field electromechanical preloading. We apply our simulation capability to electrically-tunable, soft phononic crystals consisting of periodic lattices of aligned circular-cross-section fibers embedded in a matrix and demonstrate the shifting of band gaps with electrical preloading parallel to the fibers and the opening, closing, and shifting of band gaps with electrical preloading perpendicular to the fibers. Second, we use our numerical simulation capability to detect electromechanical instabilities in dielectric elastomer composites. We consider all known electromechanical instability types: pull-in, microscopic, macroscopic, and interfacial instabilities, while surveying a comprehensive parameter space. The result is an overarching view of the instability landscape in periodic dielectric elastomer composites. Third, using our numerical simulation capability, we show that microscopic electromechanical instabilities may be harnessed to invoke reversible, electric-field-triggered pattern transformations in dielectric elastomer composites. We then assess pattern transformation as a mechanism for enhanced tunability of phononic band gaps. Additionally, we consider composites with conductive elastomer inclusions and conductive voids. Finally, we show that electric-field-triggered pattern transformation and hence band-gap tunability may be achieved in phononic crystals under complete, far-field mechanical constraint.Elastic wave propagationElastomersDielectricsPhononic CrystalsInstabilitiesPattern TransformationDielectric ElastomerEnglishRPB2019060310.26300/n2dm-1v92In CopyrightCollection is open for research.dissertations