Mechanical Engineering Commons^™

Photonic Crystal Design And Fabrication Assisted By Tunable Femtosecond Oscillator Laser, Kristofer B. Ohlinger

Theses and Dissertations - UTB/UTPA

Photonic Crystals have the potential for engineered light interaction as directed by the photonic bandgap, a property that details the prohibited propagation region and ultimately the ability to guide light. A so called, photonics-on-chip, would incorporate arbitrary light guiding with functional elements in one package. The realization of such a device is subject to the fabrication paradigms implemented and this thesis is concerned with holographic lithography as a means for creating polymer photonics crystal templates and two-photon polymerization for incorporating light guiding pathways.

In this thesis, the design of the to-be-fabricated structures has been co-opted by computational exploration of the …

A Study Of The Effect Of Vibration On Railroad Bearing Temperature, Bertha Alicia Gonzalez

Theses and Dissertations - UTB/UTPA

An on-track collaborative field test and laboratory experiments were conducted in order to determine the relationship between abrupt rises in surface temperature of a railroad bearing and vibration signatures captured during the experiments. The collaborative field test was conducted in order to investigate the root cause for this abrupt temperature change known as bearing temperature trending. The research presented in this thesis will show that temperature trending is correlated to an increase in the magnitude of vibration within the bearing and the fundamental frequencies that are generated by the internal components of a rotating bearing assembly. Distinct vibration mechanisms are …

Surface Optimization Of High Density Polyethylene And Carbon Nanofiber Composites For The Improvement Of Electromagnetic Shielding Effectiveness, Brandon C. Jarvis

Theses and Dissertations - UTB/UTPA

Nanoreinforced composites of High Density Polyethylene (HDPE) and Carbon Nanofibers (CNF) of varying nanofiber concentration were fabricated via melt mixing. Following fabrication, various metal and metal-nitride thin films were sputter deposited upon the substrates. Volume resistivity measurements of the composite substrates, as well as four point probe analysis of the composites and the deposited films were performed and are reported. Electromagnetic Interference (EMI) Shielding Effectiveness (SE) measurements were performed upon all samples in order to gauge the effects of percolation and the presence of the deposited film(s) upon overall SE. Comparisons of experimental measurements with analytical models available in the …

Design And Implementation Of An Actively Adjustable Spring Mechanism Via Redundant Actuation, Eleazar Marquez

Theses and Dissertations - UTB/UTPA

This study presents the theoretical results and experimental validation of an adjustable stiffness mechanism. The use of redundant actuation is emphasized in the design of a one-degree-of-freedom Watt II mechanism capable of independently controlling the effective stiffness without a change in equilibrium position. This approach is in contrast to previous spring mechanism designs unable to actively control the spring rate independent of deflection, and has potential applications in various types of suspension and assembly systems. Results indicate that driving the redundantly actuated, unidirectional, spring mechanism requires attaching two direct brush-type direct current motors on each of the two grounded revolute …

An Analytic Hierarchy Process Approach To Assess Health Service Quality, Yan Li

Theses and Dissertations - UTB/UTPA

While improving quality in health care is currently at the forefront of professional, political, and managerial attention, the key dimensions constituting health-care quality have not been fully understood. Also, few valid approaches have been proposed to the measurement of health-care quality. In this research, the Analytic Hierarchy Process (AHP) approach is applied to study the structure of health-care quality and deducted relative importance weights for each of the quality elements. A statistical quality model is derived to assess medical equipment quality which is an important part constituting the general health-care quality. Finally, the application of the AHP model to assess …

On Nonlinear Response Of Micro And Nano Capacitive Resonators, Martin William Knecht

Theses and Dissertations - UTB/UTPA

The nonlinear response of an electrostatically actuated micro/nano-resonator is investigated. The resonator is parametrically actuated using an electrostatic force with a first order fringe correction. Viscous damping and the Casimir effect are included. The resonator is studied using the Method of Multiple Scales in a direct approach of the problem and then compared numerically using a Reduced Order Model based on the application of a Galerkin procedure. In addition to primary resonance (ω0), parametric resonances are found at half (½ω0), twice (2ω 0), and three-halves ([special characters omitted]ω0) natural frequency. The frequency response is investigated for excitations near primary and …

A Stochastic Product Priority Optimization Method For Remanufacturing System Based On Genetic Algorithm, Xiong Xiong

Theses and Dissertations - UTB/UTPA

Increasing number of manufacturers are developing remanufacturing facilities to recover end-of-life products for product/component reuse and material recycling while the high uncertainty pattern of returned products complicates the production planning. In this thesis a stochastic production priority optimization method, considering various priority concerns for remanufacturing systems is developed. Priority ranking and matching algorithm is developed to determine the priority rule, using thirteen weighting factors. Queueing models are developed to formulate the objective function, a genetic algorithm is then developed to search optimal solution under different business configurations. Result of this research will provide insights to priority assignment mechanism, which in …

Design And Testing Of Orifice Valves For Use In Freight Railcars Hydraulic Suspension System, Awni K. Alshakhshir

Theses and Dissertations - UTB/UTPA

The work presented in this thesis describes the specific steps undertaken to design and test two spool type control valves that will be part of Amsted Rail’s innovative vertical hydraulic damper system. The design challenge lies in the requirement that these spool valves must maintain a linear relation between pressure drop, flow rate, and position, during the extension and retraction cycles of the hydraulic damper. To this end, a series of laboratory experiments were conducted on spools having different land geometries in order to acquire the optimum apertures that will produce the desired performance based on simulation data provided by …

Electrorheological Fluid Effect Of Polymer Coated Carbon Nanofibers And/Or Fullerenes In Liquid Crystals, Steven S. French

Theses and Dissertations - UTB/UTPA

An ER fluid is a ‘smart’ visco-elastic material, with flow properties influenced by external electric fields, whereby its viscosity increases within the field and returns to its inherent viscosity without the field present. This unique behavior opens many possibilities for new technologies. The optimization of ER fluid performance depends on the chemical and structural compositions of the particles in suspension and the suspension itself. Recent inclusion of nano-particles within ER fluids has shown a relationship to favorable ER trends. Therefore, this research involved nano-laden ER fluid samples of fullerenes (C60) and/or polymer coated carbon nano-fibers as the dispersed phases. These …

An Information Technology Suitability Index For Mass Customization, Oscar Leonardo Barrenechea

Theses and Dissertations - UTB/UTPA

In today’s manufacturing world, high competitive markets are pushing companies to find better ways to satisfy their customer’s needs using several Mass Customization (MC) approaches. Consequently, new Information Technologies (IT) have taken a very important role in order to manage the increasing amount of data generated from those customers. The purpose of this thesis is to develop an IT suitability index for MC that would help to identify the critical IT factors to be addressed in order to efficiently support MC. A linear programming regression model was utilized to generate index values. Finally, the results of this model could be …

Gas-Assisted Powder Injection Molding: A Comparison Of Residual Wall Thickness Between Metal Cavity Vs. Sla Cavity And Effect Of Mold Temperature On Residual Wall Thickness, Donghan Kim

Theses and Dissertations - UTB/UTPA

The effects of processing variables on gas penetration depth and Residual Wall Thickness (RWT) in an aluminum (Al) cavity of Gas-Assisted Injection Molding (GAIM) were investigated with Polypropylene (PP) and Stainless Steel Powder Feedstock (SSPF). The selected processing variables were melt temperature, shot size, gas pressure, and gas delay time. By using a Taguchi L9 array, the results were compared with previous work. For PP, there were no significant differences on gas penetration depth. However, the significance of gas delay time was relatively higher in an Al cavity as compared to a Stereolithography (SLA) cavity from previous work with SSPF. …

Thermal Analysis Of Railroad Bearings: Effect Of Wheel Heating, Lariza A. Navarro

Theses and Dissertations - UTB/UTPA

Catastrophic bearing failure is a major concern for the railroad industry because it can lead to costly train stoppages. Excessive heat buildup within the bearing is one of the main factors that can warn of impending failure. The work presented in this thesis is motivated by the need to understand the heat transfer paths to the bearing when wheel heating occurs. A series of experiments and finite element analyses were conducted in order to quantify the different heat transfer mechanisms, with emphasis on radiation. The results indicate that the effect of thermal radiation is minimal when the wheel tread temperature …

A Comprehensive Study Of The Extensional Rheology Of Complex Fluids, Manojkumar Chellamuthu

Doctoral Dissertations 1896 - February 2014

Non-Newtonian fluids play an important role in our daily life. The visco-elastic nature of these fluids comprises a class of materials found in variety of items ranging from food, to plastic products, to the cosmetic products. The design and tunability of non-Newtonian fluids is only possible through an understanding of their complex dynamics and rheology. In this thesis, a filament stretching rheometer is used to investigate the extensional rheology of three important classes of complex visco-elastic fluids namely surfactants, suspensions and polymers.

Surfactants with their unique molecular amphiphilic chemistry allow them to form long wormlike micellar structures, which behave like …