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Simulation Based Modeling Of The Elastic Properties Of Structural Wood Based Composite Lumber, Laszlo Bejo
Simulation Based Modeling Of The Elastic Properties Of Structural Wood Based Composite Lumber, Laszlo Bejo
Graduate Theses, Dissertations, and Problem Reports
The importance of wood-based composite lumber is increasing in the US market for construction materials. Manufacturers of such composites strive to make their products more competitive by increasing their value. This dissertation describes the development of simulation models that can aid these efforts by estimating the elastic characteristics of composite lumber products. The study included the assessment of the orthotropic mechanical properties of the raw material, the effect of densification it experiences during the hot-pressing procedure, and the geometric structure of the composites. Using the results of these investigations, computer models were created based on principles of deterministic and stochastic …
Design And Analysis Of A Hybrid Steel/Composite Pipe For High-Pressure Applications, William Jennings Briers Iii
Design And Analysis Of A Hybrid Steel/Composite Pipe For High-Pressure Applications, William Jennings Briers Iii
Graduate Theses, Dissertations, and Problem Reports
Once limited almost exclusively to aerospace applications, the use of composite materials has become widespread among many high performance industries. Today's petroleum industry is requiring piping systems to sustain high pressures, impact, rugged handling, and harsh environmental conditions such as corrosion and temperature. Advances in the last decade of engineered materials have opened the way for more conversions from metal to composites.;The objective of this research is to develop a lightweight composite pipe that meets the performance requirements of an existing high-pressure steel pipe. This development is crucial to the petroleum industry where hydraulic-fracturing services are demanding lighter weight materials …
Studies Of The Initial Stage Of Silicon Carbide Growth On Silicon, Katherine Stewart Ziemer
Studies Of The Initial Stage Of Silicon Carbide Growth On Silicon, Katherine Stewart Ziemer
Graduate Theses, Dissertations, and Problem Reports
The lack of understanding concerning the initial stage of silicon carbide (SiC) growth on silicon (Si) substrates gives rise to heated debates on the growth mechanisms, the characteristics of the "optimal" initial layers, and the processing parameters necessary to produce high-quality cubic or beta silicon carbide (beta-SiC) on these initial layers. If the potential of beta-SiC as a semiconductor for electronic devices is to be realized, the growth of the initial layers (i.e. the initial stage of growth) must be understood and then controlled.;This dissertation presents results from the comparison of the initial stages of beta-SiC growth by gas source …
Computational Modeling Of Hydrogen Embrittlement Of Iron Aluminides, Roxana Cisloiu
Computational Modeling Of Hydrogen Embrittlement Of Iron Aluminides, Roxana Cisloiu
Graduate Theses, Dissertations, and Problem Reports
Comparative fracture tests of two Fe-28%Al iron aluminides revealed that alloys with B, Zr, and C addition (FA189) are extrinsically more susceptible to environmental embrittlement than the base ternary alloy (FA186) under constant tensile loading condition. This may due to the effect of smaller grain sizes caused by alloy addition. To further investigate the grain boundary size effect as related to the susceptibility of hydrogen embrittlement, comparative finite element modeling simulations of intergranular fracture of two iron aluminides (FA186 and FA189) were carried out. The computational simulations involved sequentially coupled stress and hydrogen diffusion analyses to determine crack-tip stress state …
Photoluminescence Study Of Cadmium Zinc Telluride, Swati Jain
Photoluminescence Study Of Cadmium Zinc Telluride, Swati Jain
Graduate Theses, Dissertations, and Problem Reports
In this thesis, I present a detailed study of Cd1-xZn xTe crystals with 0 ≤ x ≤ 0.14 using photoluminescence (PL) spectroscopy in the temperature range from 5 K to 300 K with the purpose of: (1) identifying various radiative transitions that are signatures of various point defects in bulk CdZnTe, (2) determining the zinc concentration in these crystals, and (3) identifying the nature of room-temperature PL. PL spectra at 5 K was used to determine the bandgap and hence the zinc concentrations. In the current state-of-the-art CZT grown for radiation detectors, it is common to observe 5-K PL spectra …
Growth Kinetics And Doping Of Gallium Nitride Grown By Rf-Plasma Assisted Molecular Beam Epitaxy, Aaron Joseph Ptak
Growth Kinetics And Doping Of Gallium Nitride Grown By Rf-Plasma Assisted Molecular Beam Epitaxy, Aaron Joseph Ptak
Graduate Theses, Dissertations, and Problem Reports
A reduced rate for growth of GaN by plasma-assisted molecular beam epitaxy often limits growth to temperatures less than 750°C, with the reduction significantly larger than thermal decomposition rates. Conditions producing a flux consisting predominantly of either atomic nitrogen or nitrogen metastables have been established using various rf-sources. Atomic nitrogen, possibly coupled with the presence of low energy ions, is associated with the premature decrease in growth rate. An active nitrogen flux consisting primarily of nitrogen metastables produces a temperature dependence more consistent with decomposition rates. Growth with molecular nitrogen metastables results in significantly improved electrical properties.;Magnesium incorporation was studied …
High-Temperature Stress-Accerated Grain Boundary Oxidation Mechanism On Inconel 783 Superalloy, Cezar Cisloiu
High-Temperature Stress-Accerated Grain Boundary Oxidation Mechanism On Inconel 783 Superalloy, Cezar Cisloiu
Graduate Theses, Dissertations, and Problem Reports
Under high temperature and stress (as in the front of the crack tip) oxygen can diffuse to the grain boundaries and react with the constitutive elements of the alloy producing brittle oxide layers, which cause the embrittlement of the material, and a brittle elastic, intergranular failure. Crack growth tests were performed on INCONEL 783 three-point-bend specimens in air and controlled oxygen atmosphere at 650°C and 538°C on two types of specimens, with and without beta-phase. Initial elastic crack growth was observed at test specimens without beta-phase. The specimens with beta-phase didn't reveal elastic crack growth. Based on the results of …
Processing And Characterization Of Contacts On Mbe-Grown Gallium Nitride, Carlo Requiao Da Cunha
Processing And Characterization Of Contacts On Mbe-Grown Gallium Nitride, Carlo Requiao Da Cunha
Graduate Theses, Dissertations, and Problem Reports
Gallium nitride, a III-V compound semiconductor, is a good candidate for applications such as blue laser diodes and power devices due to its wide bandgap. One of the main challenges related to this compound is the growth of high quality crystals. If crystals with high level of purity are grown, the carrier concentration is therefore low, and the resulting high resistivity of the bulk imposes some difficulties for capacitance-related measurements. This thesis deals with the problem of processing and characterization of contacts on highly resistive materials such as unintentionally doped n-type gallium nitride. The ideal electrical model of a depletion …