A. James Clark School of Engineering
Permanent URI for this communityhttp://hdl.handle.net/1903/1654
The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item Formation and Characterization of Transversely Modulated Nanostructures in Metallic Thin Films using Epitaxial Control(2013) Boyerinas, Brad Michael; Bruck, Hugh A; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis describes a fundamental investigation into the formation, characterization, and modeling of epitaxially-controlled self-assembly at the nanoscale. The presence of coherent nanophases and the clamping effect from an epitaxial substrate enables the formation of transversely modulated nanostructures (TMNS) resulting in improved functionality, which was previously observed through increased piezoelectric response in BiFeO3. The ability to fabricate high quality epitaxial films presents opportunity to investigate coherent phase decomposition in other material systems with multifunctional response. The research herein aims to extend the concept of nanoscale self assembly in metallic systems, including Ag-Si and Pd-PdH. First, the effect of annealing a Ag-Si couple was examined, and ordered, nanoscale Ag crystallites were observed along the interface with the epitaxial Si wafer. It is demonstrated that Ag foil can be used in place of doped Ag paste (commonly used in solar cell metallization) to achieve TMNS at the interface. It was proved that annealing the Ag-Si couple in air is necessary for the self-assembly reaction to take place, as doing so prevents bulk diffusion and eutectic melting. Electron backscatter diffraction was used to verify the epitaxial relation between the Ag nanostructures and Si crystal. A method to fabricate ordered, nanoscale PdH precipitates in epitaxial Pd thin films via high temperate gas phase hydrogenation was established. Epitaxial Pd films were deposited via e-beam deposition and a V buffer layer was necessary to induce epitaxy. This novel self-assembled nanostructure may enable hysteresis-less absorption and desorption, thus improving functionality with regard to hydrogen sensing and storage. The epitaxial Pd film was characterized before and after hydrogenation with x-ray diffraction and atomic force microscopy to determine composition and nanostructure of the film. A thermodynamic model was developed to demonstrate the possibility to control or eliminate thermodynamic hysteresis via balance of elastic interaction between the coherent interfaces of metal and metal-hydride phases and the film-substrate interface. This model can be extended to other metal-hydride systems which demonstrate coherent phase decomposition.Item Analysis of Nonlinear Behavior in Novel Pneumatic Artificial Muscles(2012) Hocking, Erica Grace; Wereley, Norman M; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Motivated by the excellent actuator characteristics of pneumatic artificial muscles (PAMs), two novel actuators based on this technology were developed for applications where traditional PAMs are not suitable. The first of these actuators is a miniature PAM that possesses the same operating principle as a full-scale contractile PAM, but with a diameter an order of magnitude smaller. The second actuator, a push-PAM, harnesses the operational characteristics of a contractile PAM, but changes the direction of motion and force with a simple conversion package. Testing on these actuators revealed each PAM's evolution of force with displacement for a range of operating pressures. To address the analysis of the nonlinear response of these PAMs, a nonlinear stress vs. strain model, a hysteresis model, and a pressure deadband were introduced into a previously developed force balance analysis. The refined nonlinear model was shown to reconstruct PAM response with higher accuracy than previously possible.