Engineering Commons^™

Residual Stress Effects On Fatigue Life Via The Stress Intensity Parameter, K, Jeffrey Lynn Roberts

Doctoral Dissertations

Residual stresses are known to have a significant effect on fatigue crack propagation and thus fatigue life. These effects have generally been quantified through an empirical approach, lending little help in the quantitative prediction of such effects. The weight function method has been used as a quantitative predictor, but its use neglects residual stress redistribution, treating the residual stress as a constant during crack growth. At least three different behaviors contribute to the redistribution of residual stress. First, the residual stress behind the crack tip is reduced to a negligible level as soon as the crack tip passes. Second, the …

Surface Modeling And Analysis Using Range Images: Smoothing, Registration, Integration, And Segmentation, Yiyong Sun

Doctoral Dissertations

This dissertation presents a framework for 3D reconstruction and scene analysis, using a set of range images. The motivation for developing this framework came from the needs to reconstruct the surfaces of small mechanical parts in reverse engineering tasks, build a virtual environment of indoor and outdoor scenes, and understand 3D images.

The input of the framework is a set of range images of an object or a scene captured by range scanners. The output is a triangulated surface that can be segmented into meaningful parts. A textured surface can be reconstructed if color images are provided. The framework consists …

Laser – Induced Nanostructures In Silicon, Jason Fowlkes

Doctoral Dissertations

This dissertation addresses the formation of nanostructures induced by the laser irradiation of silicon. A KrF (248 nm) pulsed excimer laser was used as the irradiation source. Irradiating micro – structured substrates in a reactive O2 atmosphere produced SiO nanostructures. Si nanoparticles were formed by irradiating both flat and micro – structured silicon surfaces in an inert gas ambient. On flat surfaces, low energy density irradiation (Ed < 1 J/cm2) induces the formation and clustering of a thin silicon film pulsed – laser deposited on silicon into nanoparticles that grow to 2 – 80 nm in diameter. Control over the Si nanoparticle diameter to within ± 1 nm could be obtained by optimizing the laser beam energy density, the inert gas pressure, and the number of laser pulses. The nanoparticles in the surface plane will self – organize into periodically spaced lines, if a periodic or quasi – periodic, microstructure is present at the surface.

A film of silicon nanoparticles was formed on the surface of a silicon target following pulsed laser irradiation in an inert, background gas. Silicon species generated during laser ablation were backscattered by the …

Intelligent Fault Tolerant Control For Telerobotic System In Operational Space, Sewoong Kim

Doctoral Dissertations

Telerobotic systems combine conventional teleoperation with industrial automation techniques, such as control, vision, planning, etc, to improve work efficiency, and have been expanding their applications from hazardous and remote areas to unstructured industrial uses. Unstructured environments and uncertainties in task space require human-in-the loop control to ensure and supervise safe operation since present autonomous capabilities cannot handle the vast range of tasks and uncertainties. The inherent characteristics of telerobotic systems make operational faults more likely, and require autonomous fault detection, isolation (FDI) and recovery abilities since the nature of task space makes it difficult for human operators to detect and …

The Effect Of Implantation Temperature And Ionizing Radiation On The Microstructure Of Ion Implanted Sapphire, Lawretta Chineze Leaticia Ononye

Doctoral Dissertations

Single crystalline specimens of aluminum oxide (Al_{2O3) were irradiated with boron, nitrogen and iron ions at room temperature and 1000^{oC to fluences of 1×1017 B+/cm2, 3×1016 N+/cm2 and 1×1017 Fe+/cm2 respectively with 150 keV of energy. Following irradiation, the structures were examined by several experimental techniques: transmission electron microscopy (TEM), Rutherford backscattering - ion channeling (RBS-C) spectroscopy, optical absorption measurements, x-ray diffraction (XRD) technique, and x-ray photoelectron spectroscopy (XPS). The samples implanted at room temperature were then annealed for one hour at 1000oC in a reducing (Ar-4%H2) gas and the microstructures examined.}}

The implantation temperature significantly influenced the …

A Taxonomy Of The Adoption Of Lean Production Tools And Techniques, Bradley Mullins Greene

Doctoral Dissertations

The purpose of this study is to discover if the pattern of lean tool adoption for mature lean enterprises varies by type of value stream. The study empirically tests the effect of types of production processes, production volume, and order fulfillment strategies on lean production tool adoption in mature lean enterprises. The results of the study show that each of these factors does affect the pattern of tool adoption among mature lean enterprises.

Eleven different value stream profiles are identified in the study (ex. Discrete, Low Volume, Build-to-Order, value stream such as a commercial satellite producer). A binary logistical regression …

Development Of A Model To Assess The Effect Of Ozone On Public Health Using Models-3/Cmaq, Pedro Alex Sanhueza H.

Doctoral Dissertations

According to the Clean Air Act, the establishment of priorities in air pollution control should be based on benefits to public health and welfare. Given this mandate, EPA has incorporated the health effect evaluation in the regulatory impact analysis of its rulemaking, such as Tier2 sulfur gasoline reduction and HDE diesel emission reduction. The Tennessee Department of Environment and Conservation (TDEC) has identified ozone as the primary pollutant of concern. All these antecedents provided the basis for developing a decision-making tool that helps to evaluate the various regulatory options in controlling the emission of ozone precursors from a health-effects point …

Transient Jet Interaction Force And Moment Reconstruction In Dynamic Wind-Tunnel Testing, Mark Edward Smith

Doctoral Dissertations

In recent years there has been an increased interest in understanding the effect of missile divert jets upon the pressure distribution on the surface of a missile. Missile divert jets are jets located near the missile center of mass and thrusting along a lateral axis of a missile. The firing of a divert jet perturbs the pressure dis- tribution and thus alters the aerodynamic force acting on the missile. This is the aerodynamic jet interaction e®ect. It is essential to characterize and understand this effect when designing robust missile autopilots.

Testing techniques for determining the transient jet interaction effect must …

Molecular Characterization Of The T(4;9)12gso Mutation And Analysis Of The Associated Fitness, Skeletal, And Lymphoproliferative Phenotypes, Laura Ray Chittenden

Doctoral Dissertations

The t(4;9)(B3;E3.2)12Gso reciprocal translocation is an autosomal recessive mouse mutation involving chromosome 4, band B3 (Mmu4B3) and chromosome 9, band E3.2 (Mmu9E3.2). The most striking phenotype of the 12Gso homozygote involves axial skeleton deformities, resulting in significant shortening of body length, scoliosis, displaced hips and kinky tails. Homozygous animals are significantly smaller than normal littermates and frequently exhibit early lethality, as many of the mutants perish by 1 day postnatal, and many others do not survive the three weeks to weaning age. Homozygous 12Gso mice also develop an unusual bone marrow defect that closely resembles leukemia. The penetrance of the …

High-Temperature, High-Resolution A/D Conversion Using 2nd- And 4th-Order Cascaded Σδ Modulation In 3.3-V 0.5Μm Sos-Cmos, M. Nance Ericson

Doctoral Dissertations

Sigma Delta Modulation is an oversampling technique commonly used in high-resolution analog-to-digital conversion. By employing oversampling and quantization noise shaping, the method allows very high-resolution conversion using low-resolution functional blocks. A multitude of architectural variations of this oversampled class of digitizers has been explored and reported in research literature for a wide variety of applications including seismic imaging, general low-bandwidth high-resolution instrumentation, audio conversion, and most recently high-speed communications.

Data conversion associated with seismic imaging has been recently dominated by this class of converters, though all data acquisition systems require environmental control, preventing placement of the digitizing electronics down-hole. The …

An Information Approach To Regularization Parameter Selection For The Solution Of Ill-Posed Inverse Problems Under Model Misspecification, Aleksey M. Urmanov

Doctoral Dissertations

Engineering problems are often ill-posed, i.e. cannot be solved by conventional data-driven methods such as parametric linear and nonlinear regression or neural networks. A method of regularization that is used for the solution of ill-posed problems requires an a priori choice of the regularization parameter. Several regularization parameter selection methods have been proposed in the literature, yet, none is resistant to model misspecification. Since almost all models are incorrectly or approximately specified, misspecification resistance is a valuable option for engineering applications.

Each data-driven method is based on a statistical procedure which can perform well on one data set and can …

System Impact Of Silicon Carbide Power Electronics On Hybrid Electric Vehicle Applications, Burak Ozpineci

Doctoral Dissertations

The emergence of silicon carbide- (SiC-) based power semiconductor switches with their superior features compared with silicon (Si) based switches has resulted in substantial improvements in the performance of power electronics converter systems. These systems with SiC power devices are more compact, lighter, and more efficient, so they are ideal for high-voltage power electronics applications including hybrid electric vehicle (HEV) power converters.

In this dissertation, first, a power supply converter and a traction drive converter of an HEV are selected and then, the impact of SiC-based power devices on these converters is investigated. Reductions in heatsink size and device losses …

Computational Investigation Of The Discharge Coefficient Of Bellmouth Flow Meters In Engine Test Facilities, Charles Lynn Sebourn

Doctoral Dissertations

In this thesis computation of the discharge coefficient of bellmouth flow meters installed in engine test facilities is presented. The discharge coefficient is a critical parameter for accurately calculating flow rate in any flow meter which operates by means of creating a pressure differential. Engine airflow is a critical performance parameter and therefore, it is necessary for engine test facilities to accurately measure airflow.

In this report the author investigates the use of computational fluid dynamics using finite difference methods to calculate the flow in bellmouth flow meters and hence the discharge coefficient at any measurement desired.

Experimental boundary layer …

An Experimental And Numerical Study Of Open Cavity Flows, Sekhar Radhakrishnan

Doctoral Dissertations

This work is part of an ongoing study aimed at understanding of cavity flow oscillations. An experimental setup was designed, constructed, and tested to measure the Sound Pressure Levels (SPL) on the floor of four cavities, and to quantitatively visualize the flow-field inside the cavity. Measurements were made for a fixed cavity width by depth ratio of 3.33, for four length by depth (L/D) ratios of 2.0, 2.5, 3.5 and 4.5. Using Particle Image Velocimetry (PIV), the cavity velocity fields were obtained at subsonic speeds ranging from Mach 0.3 to Mach 0.6. Numerical simulations were performed for cavity geometry configurations …