Mechanical Engineering Commons^™

Assessment Of Abaqus Capabilities For Crack Growth And Calculation Of Energy Release Rate, Luis Alonso Hernandez

Open Access Theses & Dissertations

The purpose of this study was to benchmark ABAQUS modeling capabilities for crack propagation and calculation of energy release rate against closed-form analytical solutions. The crack growth capability for this study was evaluated using the following techniques: virtual crack closure technique (VCCT), X-FEM coupled with VCCT, and X-FEM coupled with cohesive segments. The capability of calculating the energy release rate was assessed by using the J-integral routine. A Double Cantilever Beam (DCB) specimen was used to conduct the study for mode I propagation, and a mixed mode bending (MMB) specimen was used to study the propagation for mixed mode I/II …

Experimental Study On The Fabrication Of Advanced Materials For Energy Applications Using High Energy Mechanical Milling, Ashvin Kumar Narayana Swamy

Open Access Theses & Dissertations

The reaction of aluminum (Al) powder with water has the potential for on demand hydrogen generation. Conventional Al powders, however, react with water slowly due to a highly protective oxide layer on the particle surface. Current methods for Al activation involve harmful and expensive materials. The nano-scale Al powders also remain very expensive and have problems such as a large amount of oxide on the surface. The use of aluminum in an energy generation cycle is also hindered by the fact that, although Al is the most abundant metal in the Earth's crust, its recovery from ore consumes a lot …

Effect Of Hafnium-Incorporation On The Microstructure And Dielectric Properties Of Cobalt Ferrite Ceramics, Stephen Josiah Wells

Open Access Theses & Dissertations

The effect of hafnium ion (Hf⁴⁺) incorporation in cobalt ferrite (CFO) was studied. Samples of Hf substituted CFO ceramic (CoFe_2-xHf_xO₄), were synthesized in the laboratory with hafnium concentrations ranging from x=0.000 to x=0.200. X-ray diffraction scans show that the Hafnium CFO crystalizes in the inverse spinel phase. Inclusion of hafnium causes lattice expansion, increasing the lattice parameter from 8.374 í? for pure CoFe2O4 to 8.391 í? for the highest concentration of hafnium tested (x=0.020). The dielectric properties of CFO are greatly enhanced by inclusion of hafnium. The enhancement is due to the …

Thermal Barrier Coatings (Tbc's) For High Heat Flux Thrust Chambers, Christopher Michael Bradley

Open Access Theses & Dissertations

The last 30 years materials engineers have been under continual pressure to develop materials with a greater temperature potential or to produce configurations that can be effectively cooled or otherwise protected at elevated temperature conditions. Turbines and thrust chambers produce some of the harshest service conditions for materials which lead to the challenges engineers face in order to increase the efficiencies of current technologies due to the energy crisis that the world is facing. The key tasks for the future of gas turbines are to increase overall efficiencies to meet energy demands of a growing world population and reduce the …

A Block Operator Splitting Method For Heterogeneous Multiscale Poroelasticity, Paul M. Delgado

Open Access Theses & Dissertations

Traditional models of poroelastic deformation in porous media assume relatively homogeneous material properties such that macroscopic constitutive relations lead to accurate results. Many realistic applications involve heterogeneous material properties whose oscillatory nature require multiscale methods to balance accuracy and efficiency in computation.

The current study develops a multiscale method for poroelastic deformation based on a fixed point iteration based operator splitting method and a heterogeneous multiscale method using finite volume and direct stiffness methods. To characterize the convergence

of the operator splitting method, we use a numerical root finding algorithm to determine a threshold surface in a non-dimensional parameter space …

Nanocomposite And Mechanically Alloyed Reactive Materials As Energetic Additives In Chemical Oxygen Generators, Marco Antonio Machado

Open Access Theses & Dissertations

Chemical oxygen generators are widely used for aircraft, spacecraft, submarines, and mine rescue. Oxygen-generating compositions typically include alkali metal chlorate or perchlorate that decomposes at increased temperatures, a transition-metal oxide as a decomposition catalyst, and a metal fuel that reacts with part of the produced oxygen to provide heat for a self-sustained propagation of the decomposition/combustion wave. To increase the oxygen yield per unit mass, it is of interest to minimize the amount of metal fuel, but decreasing its content leads to pulsating combustion and undesired fluctuations of the oxygen flow rate. This work explores the feasibility of replacing iron …

Development Of A Thermal Imaging Feedback Control System In Electron Beam Melting, Emmanuel Rodriguez

Open Access Theses & Dissertations

The Electron Beam Melting (EBM) process is a promising technology in the rapid manufacturing of metal components. EBM has the potential to reduce the cost of metal parts by minimizing the use of raw materials and machining time. The EBM technology has several advantages over other additive manufacturing (AM) technologies of metal, such as manufacturing speed and mechanical properties of the finished parts. For the process to be accepted in the aerospace industry as a flight-ready manufacturing technology, however, improved control and feedback must be implemented in the building process for better part quality and uniform production in manufacturing. As …

Modeling, Numerical Analysis, And Predictions For The Detonation Of Multi-Component Energetic Solids, Michael Wayne Crochet

LSU Doctoral Dissertations

Metal powders are often used as an additive to conventional high explosives to enhance the post-detonation blast wave. Piston-impact simulations are commonly utilized to predict performance metrics such as detonation speed and strength, as well as assessing the impact and shock sensitivity of these materials. The system response is strongly influenced by the initial particle size distribution and material composition. Multiphase continuum models have been routinely applied at the macroscale to characterize the detonation of solid high explosives over engineering length scales. Current models lack a description of the physically permissible constitutive relations for mass transfer due to general chemical …

Polymer-Based Fluidic Devices Integrated With Perforated Micro- And Nanopore Membrane For Study Of Ionic And Dna Transport, Junseo Choi

LSU Doctoral Dissertations

This study aims to develop a process, allowing a low-cost and high-throughput fabrication technique to produce freestanding polymer membranes having perforated micro- and nanopores, and also to design 3D micro/nanofluidic devices with the membrane, enabling a study of ions and DNA transport through nanopores. Technically, we have designed and fabricated high quality silicon stamp. Then, they have been used as molds for modified nanoimprint lithography that takes advantages of a sacrificial layer to obtain freestanding polymer membrane. This technique allows easy fabrication of large area, fully released polymer membranes containing perforated micro- and sub-micropores. The membrane with perforated micropores has …

Analysis And Optimization Of Film Cooling Effectiveness, Hessam Babaee

LSU Doctoral Dissertations

In the first part, an optimization strategy is described that combines high-fidelity simu- lations with response surface construction, and is applied to pulsed film cooling for turbine blades. The response surface is constructed for the film cooling effectiveness as a function of duty cycle, in the range of DC between 0.05 and 1, and pulsation frequency St in the range of 0.2-2, using a pseudo-spectral projection method. The jet is fully modulated and the blowing ratio, when the jet is on, is 1.5 in all cases. Overall 73 direct numerical sim- ulations (DNS) using spectral element method were performed to …

Nanotube Film-Enhanced 3-D Photoanode For Application In Microsystems Technology, Fareed Dawan

LSU Doctoral Dissertations

Surface area plays an important factor in the energy conversion performance of solar cells. It has also emerged as a critical factor in the evolution of high-performance micro-electro-mechanical systems (MEMS) and multifunctional microstructures most of which will benefit from integrated on-chip solar power. Presented here is the hierarchical fabrication and characterization of TiO2 nanotubes on non-planar 3-dimensional microstructures for enhanced performance of the photoanode in dye-sensitized solar cells (DSSCs). The objective is to increase photoanode performance within a 1 cm2 lateral footprint area by increasing the vertical surface area through the formation of TiO2 nanotubes on 3-D microstructures. In the …

Steady And Unsteady Thermo-Strucural Simulation Of Thermally Actuated Micro- And Nano-Structures, Elham Maghsoudi

LSU Doctoral Dissertations

This dissertation provides a thermo-structural simulation for nano-scale and micro-scale structures with pinned and fixed boundary conditions which are either thermally positioned, buckled, or actuated. The study begins with simulating a pinned-pinned beam in micro-scale and nano-scale. The steady state thermo-structural equation is solved numerically using an implicit Finite Difference method implemented in Matlab to obtain the thermal positioning response, which is the thermally steady state center displacement, by adding a constant, time-independent heat flux to the structure. The results show the steady state thermal displacement of the system is a function of the geometry, pressure, material properties, and constant …

Investigations Of The Effects Of Flame Configuration On The Combustion Of Laminar Diffusion Flame, Li Lu

LSU Doctoral Dissertations

Motivation and objective to study double inverse diffusion flame is introduced, followed by the literature survey on soot formation in inverse diffusion flame (IDF), application of the unique structure of double inverse diffusion flame (DIDF), radiation effects on DIDF, factors that affect the formation of nitric oxide and effects of elevated pressure on diffusion flames. Numerical method is validated by the result of flame height for IDF, which is consistent with result from previous research. In present work, two DIDF burner configurations with different size are used to conduct the simulation. Ethylene is used as the fuel. For each of …

3d Integration Of Micro- And Nanostructures Into Bio-Analytical Devices, Bahador Farshchian

LSU Doctoral Dissertations

This study aims to develop a process which allows 3D integration of micro and nanostructures in microchannels. A fabrication process was established for the large area integration of hierarchical micro and nanostructures in microchannels. This novel process, which is called 3D molding, takes advantage of an intermediate thin flexible stamp such as PDMS from soft lithography and a hard mold such as brass from hot embossing process. However, the use of a thin intermediate polydimethylsiloxane (PDMS) stamp inevitably causes dimensional changes in the 3D molded channel, with respect to those in the brass mold protrusion and the intermediate PDMS stamp …

Developing Defect-Tolerant Demolding Process In Nanoimprint Lithography, Alborz Amirsadeghi

LSU Doctoral Dissertations

Demolding, the process to separate stamp from molded resist, is most critical to the success of ultraviolet nanoimprint lithography (UV-NIL). In the present study we first investigated adhesion and demolding force in UV-NIL for different compositions of a model UV-curable resist containing a base (either tripropyleneglycol diacrylate with shorter chain length or polypropyleneglycol diacrylate with longer chain length), a cross-linking agent (trimethylolpropane triacrylate) and a photoinitiator (Irgacure 651). The demolding force was measured using a tensile test machine after imprinting the UV resist on a silicon stamp. In general, the shorter monomer shows a larger demolding force. Decreasing the cross-linking …

Thermal Cycling And Thermal Radiation Performances Of Novel Thermal Barrier Coatings, Li Wang

LSU Doctoral Dissertations

Thermal barrier coatings (TBCs) play an important role in protecting the superalloy components from the hot gas stream in gas-turbine engines. Driven by the higher inlet temperature of modern gas turbine engines for higher efficiency and less harmful gas emission, exploration of TBC new materials and thermal radiation effects of TBCs have attracted more attentions recently. In this study, thermochemical compatibility of Gd2Zr2O7 (GZ) and yttria-stabilized-zirconia (YSZ) at 1300 ºC was investigated. Single, double and three ceramic-layered GZ based TBCs were prepared and their thermal cycling properties were performed under different thermal conditions. Thermochemical compatibility investigation showed that YSZ tended …

Fabrication And Characterization Of A Polymeric Nanofluidic Device For Dna Analysis, Jiahao Wu

LSU Doctoral Dissertations

The growing needs for cheaper and faster sequencing of long biopolymers such as DNA and RNA have prompted the development of new technologies. Among the novel techniques for analyzing these biopolymers, an approach using nanochannel based fluidic devices is attractive because it is a label-free, amplification-free, single-molecule method that can be scaled for high-throughput analysis. Despite recent demonstrations of nanochannel based fluidic devices for analyzing physical properties of such biopolymers, most of the devices have been fabricated in inorganic materials such as silicon, silicon nitride and glass using expensive high end nanofabrication techniques such as focused ion beam and electron …

Instability Analysis And Suppression Of Instability In Low-Density Gas Jets, Sukanta Bhattacharjee

LSU Master's Theses

A numerical study is conducted to understand the global instability of very low-density jets (as encountered in thermal plasmas). The simulations have been carried out for different parameters of density ratios, S = ƒÏj /ƒÏ‡ ranging from 0.5 to 0.03, different Reynolds numbers ranging from 500 to 4000 and different momentum thickness obtained by different extension tube length ranging from 3 to 6 diameter long. The flow parameters and vortex structures has been visualized to understand the details of the evolution of the flow field. The axisymmetric shear layer rolls up in the near field of the jet forming vortex …

Effect Of Rest Time On Heart Rate, Perceived Exertion, And Strength, Amir Bahador Bahmani Bahman Beiglou

LSU Master's Theses

Finding a proper work/rest schedule is considered an important factor for improved efficiency, safety, and a higher rate of productivity in the workplace. The purpose of this study was to determine the optimum rest period for lifting tasks using heart rate, perceived exertion, and physical strength. First, the maximum acceptable weight of the box to be lifted was determined for each one of 10 participants using a psychophysical approach. Then on separate days, participants were required to repetitively lift the box from knuckle height to shoulder height for 20 minutes. They were then allowed to rest 5, 10, 15, or …

Effect Of Surface Roughness On The Efficiency Of Self-Healing Polymers, Ifeanyi Janarus Okoro

LSU Master's Theses

A shape memory polymer (SMP) is a smart material capable of maintaining two distinct shapes depending on its temperature. A SMP is soft at temperatures above its glass transition temperature but hard below it. When copolyester thermoplastic additives are dispersed in a SMP, it becomes a SMP-based particulate composite capable of self-healing at both the molecular level and the structural level. This makes it very desirable for industrial applications. Upon damage to the composite, the surfaces at the damage interface have to come into contact for efficient healing; the shape memory effect, coupled with a confined recovery (healing) process, ensures …