Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 40 for “"Polycrystals"”.
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Microstructure-informed modeling of hydrogen diffusion in zirconium polycrystals
Zirconium alloys are widely used in the core of various types of nuclear reactors. During service, the hot water coolant reacts with zirconium and releases hydrogen atoms that ingress into the lattice of the metal alloy. With time, hydrogen concentration exceeds its terminal solid solubility limit …
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Scale-Dependent Homogenization and Scaling Laws in Random Polycrystals
… bounds on the response of multifarious random polycrystals. In doing so, one infers the approach to the Representative Volume Element (RVE), the cornerstone of the separation of scales in continuum mechanics. The RVE is approached by setting up and solving stochastic Dirichlet and Neumann …
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Compositional dependence of physical properties in nickel-manganese-gallium polycrystals
Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1997.
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The Competing Effects of Slip and Twinning on the Deformation of Hadfield Manganese Steel Single and Polycrystals
A similar study on the 316L stainless steel single crystals indicated that the addition of nitrogen lead austenitic stainless steel to exhibit deformation mechanisms, orientation and temperature dependence similar to Hadfield steel. Therefore, it is concluded that the mechanical behavior of fcc …
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Dielectric and electromechanical properties of barium and zirconium co-doped sodium bismuth titanate
… properties of single crystals and polycrystals for this new family of relaxor perovskite ferroelectrics are presented. The actuation and polarization characteristics in this system were found to be highly sensitive (within 2 mol%) to cation doping levels, and tailored compositions …
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Computer Modeling and Simulation of Morphotropic Phase Boundary Ferroelectrics
… properties in single crystals and polycrystals of perovskite-type ferroelectrics around the morphotropic phase boundary (MPB). The findings include: (I) Coherent phase decomposition near MPB in PZT is investigated. It reveals characteristic multidomain microstructures, where …
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Multiscale Experimental Study on the Effect of Texture and Anisotropy on the Thermomechanical Response of Zirconium
… appearance of energy storage in basal textured polycrystals is explained by the presence of localized deformation. Experimental and numerical techniques are used to study the microstructural origins of an inhomogeneous response and the multiscale nature of its development. In situ full field …
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A Detailed Investigation of the Strain Hardening Response of Aluminum Alloyed Hadfield Steel
… crystallographic orientations, and finally the polycrystals of the aluminum alloyed Hadfield steel. Meanwhile, the capability of the model to predict texture was also observed through the rotation of the loading axis in single crystals. The ability of the model to capture the polycrystalline …
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Polycrystalline Grain Boundary Solute Segregation at Finite Sizes and Temperatures
… of grain boundary data are still limited for polycrystals that contain a profuse spectrum of grain boundary sites, especially for the effects of grain size and temperature on grain boundary site spectra. This thesis aims to fill the literature gap by providing a framework for studying grain …
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Grain constraint and size effects in shape memory alloy microwires
… microstructure is not as complex as that of polycrystals either: we call this new class of shape memory alloys oligocrystals. This thesis seeks to better understand the relationship between microstructure and properties in these alloys through a combination of mechanical testing, in situ …
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Microstructure-based modeling of damage and healing in salt rock with application to geological storage
… the viscoplastic and damage behavior of halite polycrystals is upscaled from mono-crystal slip mechanisms. The model provides micro-mechanical interpretations to important aspects of salt rock viscoplastic and fatigue behavior. We implemented the micromechanical model in a finite element program …
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The Spectral Model of Grain Boundary Solute Segregation
… disordered and anisotropic nature of GBs in polycrystals, which results in a spectrum of solute segregation tendencies (energies). In this thesis, we aim to address and remove this simplification; the thesis has five major contributions. First, we elucidate computationally the nature of this …
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Phase-and-Defect Diagrams for Polycrystalline Grain Boundary Segregation
… a spectral regular solution model of segregated polycrystals. I use this framework to derive a fully spectral free energy function and demonstrate how it can be used to develop a self-consistent phase-and-defect diagram which considers the bulk regular solution and the segregated polycrystalline …
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Edge-defined film-fed growth of single-crystal piezoelectrics
… and piezoelectric actuation has been observed in polycrystals and flux-grown <100> single-crystals of ... Using seeded, Edgedefined Film-fed Growth (EFG) and the related Stepanov Technique (ST), low-hysteresis, highstrain, <100> and <111> oriented, single-crystals of BNBZT can be grown in rod and …
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The microstructure and properties of hipped powder Ti alloys
… in the PREP powder were either coarse grained polycrystals or single crystals. These differences led to significant differences in the microstructures and properties of HIPped samples. It was found that HIPping of Ti-6Al-4V samples resulted in the formation of equiaxed regions and lath-like …
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On the role of lattice defects interactions on strain hardening: A study from discrete dislocation dynamics to crystal plasticity modelling
… performing DDD simulations in low-symmetry polycrystals. The information extracted from the collective dislocation interactions are then passed to a series of constitutive models, and later used to quantify their effects at the scale of the polycrystal. For such purpose, a constitutive …
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Quantification of Elastic Incompatibilities at Triple Junctions via Physics-Based Surrogate Models
… sources of grain boundary incompatibilities in polycrystals and potential mitigation strategies through microstructure manipulation. Thus, understanding the relationship between grain incompatibility and failure is important for the practical use of polycrystalline materials. Surrogate models …
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BaTiO₃ based materials for piezoelectric and electro-optic applications
… phase. These materials were prepared as bulk polycrystals using a standard solid-state reaction technique in order to test the piezoelectric and dielectric properties. Some compositions were then chosen for thin film deposition. The films were deposited using pulsed laser deposition on MgO and …
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Three Dimensional Characterization of Deformation Twins Using Synchrotron X-Ray Diffraction
… The two main deformation modes in HCP polycrystals are slip and twinning. While deformation by slip is well understood, many fundamental questions about twinning are still remained unanswered. The aim of this research is to employ a novel experimental technique, three-dimensional …
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Fractals in mechanics of materials
… and Mohr-Coulomb models for rocks and soils. Polycrystals and thermo-elasto-plastic materials are also investigated. The fractal character of many porous materials motivates the second part of this dissertation: theoretical modeling of fractally microstructured materials. Using dimensional …
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