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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Modeling Texture Evolution in Polycrystalline Materials Using Spherical Harmonics

Unknown Date (has links)
For decades the prime role of metallurgists has been to optimize material microstructure for performance by designing and applying appropriate thermo-mechanical processing steps. Until recently the study of the relationships between processing and microstructure has largely remained within the purview of experimental metallurgists because the mechanisms that contribute to the microstructural changes are very complex, and the changes occur either simultaneously or successively to varying degrees, depending on location within the material. The development of computational models for predicting the overall response of materials to such a complex microstructural changes is extremely difficult. However, recent advances in high-performance computing have led to considerable progress in addressing this challenge. This study addresses this question by focusing on the textural point of view which in this work is represented by the crystallographic texture (also called Orientation Distribution Function or ODF). The textural representation of the material is expanded in terms of spherical harmonics. Developing such approach is a crucial to advances in material-by-design. This model is based on a conservation principle in the orientation space. It links any desired final microstructure of a polycrystalline material to a given initial state. To investigate a typical processing example of deformation in tension, compression and rolling for isotropic copper, an FCC material, a microstructure is numerically simulated using a Taylor type model. Taylor models are known to correctly fit the deformation of cubic microstructures. A first goal is to determine the number of texture coefficients and their values for different expansions of the Fourier series. The second to use the texture coefficients in a processing path model to predict the microstructure evolution. The difference between the experimental and the predicted texture coefficients will be evaluated using the root mean square deviation for various expansions of the Fourier series. Also it is necessary to know how small a step size one needs to use in the numerical discretization of the deformation process. To increase accuracy we introduce Richardson extrapolation. This method allows us to increase the size of the discretization step and result in a small error. For hexagonal close-packed materials, the Taylor model is not applicable. Therefore to verify the processing path model for the example of commercially pure titanium, the texture evolution matrix is modeled using experimental data obtained for cold and warm rolling. The model appears to be of good accuracy. To examine how much of the possible microstructural material properties are achievable using typical deformation processes, the microstructural evolution is visualized within the microstructure hull. The results suggest that vast amounts of possible microstructural configurations are unexplored by those classical deformation methods. / A Dissertation submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Summer Semester, 2006. / June 19, 2006. / Processing Path, Texture Evolution, Spherical Harmonics, Material by Design / Includes bibliographical references. / Hamid Garmestani, Professor Co-Directing Dissertation; Justin Schwartz, Professor Co-Directing Dissertation; Young Park, Outside Committee Member; Leon Van Dommelen, Committee Member.
2

Validation Studies of SC/Tetra Code in 2D and 3D Simulations

Mao, Shuo 13 May 2014 (has links)
No description available.
3

Fatigue Based Structural Design Exploration via Engineering Data Analytics

Li, Hao 19 August 2014 (has links)
No description available.
4

Dynamic Modeling of Thermal Management System with Exergy Based Optimization

Bracey, Marcus J. 01 September 2017 (has links)
No description available.
5

Experimental Studies of Turbulent Boundary Layers Over a Rough Forward-facing Step and its Coarse Scale Resolution Approximations

Ren, Huiying 16 December 2010 (has links)
No description available.
6

Effect of Cooling Rate and Mold Counter Pressure on the Crystallinity and Foaming Control In Microcellular Injection Molded Polypropylene Parts

Cousineau, Jeffrey Scott 09 July 2012 (has links)
No description available.
7

EFFECT OF PROCESS VARIABLES ON SUB-MELT THERMAL BEHAVIORAND SOLID-STATE PHASE TRANSFORMATIONS IN BEAM-BASEDADDITIVE MANUFACTURING OF TI-6AL-4V

Doak, Heather N. 27 August 2013 (has links)
No description available.
8

Vehicle Level Transient Aircraft Thermal Management Modeling and Simulation

Donovan, Adam 30 August 2016 (has links)
No description available.
9

Numerical simulation of effects of cladding and superimposed hydrostatic pressure on fracture in metals under tension.

Chen, Xiaoxian January 2009 (has links)
<p>In this study, detailed numerical works are carried out to investigate cladding<br />and superimposed hydrostatic pressure on fracture in metals under tension by using<br />finite element software ABAQUS/Explicit. It is concluded that both cladding and<br />superimposed hydrostatic pressure delay void nucleation and void growth, which<br />results in increasing fracture strain in metals under tension.<br />The influence of cladding on delaying fracture in metals under tension is<br />numerically studied by employing Gurson-Tvergaard-Needleman (GTN) damage<br />model. It is found that cladding has a significant effect on enhancement in materials'<br />ductility due to the fact that cladding increases necking strain which in tum delays the<br />void nucleation and growth. Topological arrangement of cladding in axisymmetric<br />tensile round bars shows no noticeable effect on necking but significantly affects<br />fracture strain.<br />The influence of superimposed hydrostatic pressure is numerically<br />investigated on sheet metals under plane strain tension by using GTN damage model.<br />It is found that superimposed hydrostatic pressure has no noticeable effect on necking<br />but significantly delays fracture initiation due to the fact that superimposed<br />hydrostatic pressure delays or completely eliminates the nucleation, growth and<br />coalescence of microvoids or microcracks.</p> / Master of Applied Science (MASc)
10

A Numerical and Experimental Study Of Ion-Drag Electrohydrodynamic Micropumps

Hasnain, Mohammed Syed January 2010 (has links)
<p>The objectives of this work are (i) to develop a numerical model for electrohydrodynamic micropumps, (ii) to investigate the effect of using a conductive agent in the working fluid to enhance the pump performance and (iii) to investigate the use of pulse voltage on EHD micropumps.</p> <p>A numerical model was developed that incorporates a charge model at the emitter electrode that is coherent to the electric field. The model results were found to be in good agreement with previous experimental results. A parametric study was performed to investigate the effect of the channel height and multi-stage spacing on the pump performance. Reducing the channel height reduced the flow rate but increased the pressure head, while increasing the multi-stage spacing improved the pump performance.</p> <p>The effect of using conductive agents in the working fluid was investigated using Ferrocene in HFE-7100. The Ferrocene was found to significantly improve the pump performance. However, at high voltages, the pressure could not be sustained for long periods of time. The effect of an applied pulse voltage on the performance of the micropumps was studied. A maximum pressure 3512 Pa was achieved at an applied pulse voltage between 500 V to 800V, pulse repetition rate of 5 Hz, and duty cycle of 60%.</p> / Master of Applied Science (MASc)

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