Global ETD Search

281	The Pore Structure of Indiana Limestone and Pink Dolomite for the Modeling of Carbon Dioxide in Geologic Carbonate Rock Formations Freire-Gormaly, Marina 22 November 2013 (has links) The primary objective was to predict the relative storage capacity of carbonate rocks relevant for carbon dioxide sequestration. To achieve this, a detailed pore scale characterization of model carbonate rocks, Indiana Limestone and Pink Dolomite, was conducted utilizing micro-computed tomography (microCT) data using pore network modeling and invasion percolation simulations. For the first time in literature, Pink Dolomite’s pore space characteristics were analyzed. A secondary objective was to compare thresholding techniques as applied to carbonates which exhibit dual porosity (porosity at multiple length scales). The analysis showed the sensitivity of existing methods to the thresholding technique, imaging method and material. Overall, the contributions of this work provide an assessment of two carbonates relevant for carbon capture and storage at the pore scale; and a preliminary assessment into thresholding dual porosity carbonates. carbon capture and storage microsctructure Indiana Limestone Pink Dolomite pore network modeling carbonate rocks micro-computed tomography microCT scanning electron microscopy SEM thresholding microporosity dual porosity saline aquifer 0548 0372 0775 0794 0765
282	Evolution and Environmental Degradation of Superhydrophobic Aspen and Black Locust Leaf Surfaces Tranquada, George Christopher 17 July 2013 (has links) The current study is focused on the characterization of four natural leaf species (quaking, bigtooth and columnar european aspen as well as black locust) possessing a unique dual-scale cuticle structure composed of micro- and nano-scale asperities, which are able to effectively resist wetting (superhydrophobic), characteristic of The Lotus Effect. Scanning Electron Microscopy (SEM) was used to track the growth and evolution of their distinctive nano-scale epicuticular wax (ECW) morphologies over one full growing season. In addition, the stability of their superhydrophobic property was tested in various environments. It was determined that the long-term stability of these surfaces is tentatively linked to various environmental stress factors. Specifically, a combination of high temperature and humidity caused the degradation of nano-scale asperities and loss of the superhydrophobic property. The dual-scale surface structure was found to provide a suitable template for the design of future superhydrophobic engineering materials. Superhydrophobic surfaces environmental degradation evolution of superhydrophobic leaves dual-scale roughness wear and erosion of leaf surfaces aspen and black locust leaf surfaces evolution of leaf surfaces superhydrophobic leaf surfaces cuticular damage micro and nano-scale roughness biomimetics nanomaterials epicuticular wax morphologies sensitivity to environmental stresses micro-structured materials nano-structured materials nano-scale platelets materials science nanotechnology materials engineering 0794
283	Evolution and Environmental Degradation of Superhydrophobic Aspen and Black Locust Leaf Surfaces Tranquada, George Christopher 17 July 2013 (has links) The current study is focused on the characterization of four natural leaf species (quaking, bigtooth and columnar european aspen as well as black locust) possessing a unique dual-scale cuticle structure composed of micro- and nano-scale asperities, which are able to effectively resist wetting (superhydrophobic), characteristic of The Lotus Effect. Scanning Electron Microscopy (SEM) was used to track the growth and evolution of their distinctive nano-scale epicuticular wax (ECW) morphologies over one full growing season. In addition, the stability of their superhydrophobic property was tested in various environments. It was determined that the long-term stability of these surfaces is tentatively linked to various environmental stress factors. Specifically, a combination of high temperature and humidity caused the degradation of nano-scale asperities and loss of the superhydrophobic property. The dual-scale surface structure was found to provide a suitable template for the design of future superhydrophobic engineering materials. Superhydrophobic surfaces environmental degradation evolution of superhydrophobic leaves dual-scale roughness wear and erosion of leaf surfaces aspen and black locust leaf surfaces evolution of leaf surfaces superhydrophobic leaf surfaces cuticular damage micro and nano-scale roughness biomimetics nanomaterials epicuticular wax morphologies sensitivity to environmental stresses micro-structured materials nano-structured materials nano-scale platelets materials science nanotechnology materials engineering 0794
284	Strengthening Mechanisms in Microtruss Metals Ng, Evelyn 18 December 2012 (has links) Microtrusses are hybrid materials composed of a three-dimensional array of struts capable of efficiently transmitting an externally applied load. The strut connectivity of microtrusses enables them to behave in a stretch-dominated fashion, allowing higher specific strength and stiffness values to be reached than conventional metal foams. While much attention has been given to the optimization of microtruss architectures, little attention has been given to the strengthening mechanisms inside the materials that make up this architecture. This thesis examines strengthening mechanisms in aluminum alloy and copper alloy microtruss systems with and without a reinforcing structural coating. C11000 microtrusses were stretch-bend fabricated for the first time; varying internal truss angles were selected in order to study the accumulating effects of plastic deformation and it was found that the mechanical performance was significantly enhanced in the presence of work hardening with the peak strength increasing by a factor of three. The C11000 microtrusses could also be significantly reinforced with sleeves of electrodeposited nanocrystalline Ni-53wt%Fe. It was found that the strength increase from work hardening and electrodeposition were additive over the range of structures considered. The AA2024 system allowed the contribution of work hardening, precipitation hardening, and hard anodizing to be considered as interacting strengthening mechanisms. Because of the lower formability of AA2024 compared to C11000, several different perforation geometries in the starting sheet were considered in order to more effectively distribute the plastic strain during stretch-bend fabrication. A T8 condition was selected over a T6 condition because it was shown that the plastic deformation induced during the final step was sufficient to enhance precipitation kinetics allowing higher strengths to be reached, while at the same time eliminating one annealing treatment. When hard anodizing treatments were conducted on O-temper and T8 temper AA2024 truss cores, the strength increase was different for different architectures, but was nearly the same for the two parent material tempers. Finally, the question of how much microtruss strengthening can be obtained for a given amount of parent metal strengthening was addressed by examining the interaction of material and geometric parameters in a model system. microtruss strengthening copper C11000 aluminum AA2024 cellular metal mechanical properties compressive strength densification energy modulus work hardening precipitation hardening heat treatment nanocrystalline coating aluminum oxide coating coating anodizing electrodeposition strengthening mechanisms geometry pyramidal compression buckling architecture truss uniaxial compression perforation Ramberg-Osgood Holloman nickel-iron annealing relative density periodic cellular hybrid composite microhardness stretch bend peak strength scanning electron microscopy stress strain bending stretching failure yielding column critical buckling strength critical buckling stress yield strength forming 0794
285	Strengthening Mechanisms in Microtruss Metals Ng, Evelyn 18 December 2012 (has links) Microtrusses are hybrid materials composed of a three-dimensional array of struts capable of efficiently transmitting an externally applied load. The strut connectivity of microtrusses enables them to behave in a stretch-dominated fashion, allowing higher specific strength and stiffness values to be reached than conventional metal foams. While much attention has been given to the optimization of microtruss architectures, little attention has been given to the strengthening mechanisms inside the materials that make up this architecture. This thesis examines strengthening mechanisms in aluminum alloy and copper alloy microtruss systems with and without a reinforcing structural coating. C11000 microtrusses were stretch-bend fabricated for the first time; varying internal truss angles were selected in order to study the accumulating effects of plastic deformation and it was found that the mechanical performance was significantly enhanced in the presence of work hardening with the peak strength increasing by a factor of three. The C11000 microtrusses could also be significantly reinforced with sleeves of electrodeposited nanocrystalline Ni-53wt%Fe. It was found that the strength increase from work hardening and electrodeposition were additive over the range of structures considered. The AA2024 system allowed the contribution of work hardening, precipitation hardening, and hard anodizing to be considered as interacting strengthening mechanisms. Because of the lower formability of AA2024 compared to C11000, several different perforation geometries in the starting sheet were considered in order to more effectively distribute the plastic strain during stretch-bend fabrication. A T8 condition was selected over a T6 condition because it was shown that the plastic deformation induced during the final step was sufficient to enhance precipitation kinetics allowing higher strengths to be reached, while at the same time eliminating one annealing treatment. When hard anodizing treatments were conducted on O-temper and T8 temper AA2024 truss cores, the strength increase was different for different architectures, but was nearly the same for the two parent material tempers. Finally, the question of how much microtruss strengthening can be obtained for a given amount of parent metal strengthening was addressed by examining the interaction of material and geometric parameters in a model system. microtruss strengthening copper C11000 aluminum AA2024 cellular metal mechanical properties compressive strength densification energy modulus work hardening precipitation hardening heat treatment nanocrystalline coating aluminum oxide coating coating anodizing electrodeposition strengthening mechanisms geometry pyramidal compression buckling architecture truss uniaxial compression perforation Ramberg-Osgood Holloman nickel-iron annealing relative density periodic cellular hybrid composite microhardness stretch bend peak strength scanning electron microscopy stress strain bending stretching failure yielding column critical buckling strength critical buckling stress yield strength forming 0794

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