Master of Sciences (Engineering), Case Western Reserve University, 2010, EMC - Mechanical Engineering

High Strength Low Alloy steel, grade 65 (HSLA-65) plates used by the US Navy for ship building are to be joined by Friction Stir Welding (FSW) which subjects the work-piece material to high strain rates at high temperatures. The strength of materials varies with the strain-rate and temperature to which they are subjected. Development of constitutive models to get the optimum FSW weld parameters requires experimental determination of the dynamic behaviour of a material at different strain-rates and temperatures. In the current study, experiments using the Split Hopkinson Pressure Bar (SHPB) were conducted on HSLA-65 at high temperatures to generate the true stress-strain curves in compression. In addition, two other materials, which are used in practical applications where high strain rate loading occurs at high temperatures, namely Inconel-718 superalloy (precipitation hardened and annealed) and Aluminum alloy 7075-T6 were also tested using the SHPB.

Committee: Vikas Prakash (Advisor); John Lewandowski (Advisor); Joseph Mansour (Committee Member) Subjects: Engineering; Experiments; Mechanical Engineering; Mechanics; Metallurgy

Doctor of Philosophy, Case Western Reserve University, 2006, Electrical Engineering

In this research, a monolithic, high-temperature bulk CMOS data acquisition system for Wheatstone-bridge sensors has been developed. The main design challenges were 1) excess leakage current, 2) decreased carrier mobility, and 3) unstable threshold voltage. Design techniques were developed to overcome these high-temperature effects and allow the bulk CMOS IC to operate at temperatures > 250 degree C. Two generations of data acquisition ICs have been designed and characterized: an instrumentation amplifier and a sigma-delta modulator. Both were fabricated using the AMI 1.5-µm bulk CMOS process. The Instrumentation Amplifier IC features a fully-differential, adjustable-gain amplifier with digitally programmable offset cancellation, and features a constant-gm biasing circuit, a fully monolithic oscillator, internal thermometer circuit and RTD sensor interface. The thermometer and RTD sensor interface perform well at temperatures for T < 225 degree C. The oscillator demonstrates a temperature stability of ~97 ppm/degree C for T < 290 degree C at the fast clock setting. The instrumentation amplifier shows excellent stability for T < 300 degree C. With GA = 6 and GD = 8, gain stability is 128 ppm/degree C for 25 degree C < T < 300 degree C. The Sigma-Delta IC includes a sigma-delta modulator with correlated double-sampling (CDS) pre-amplifier, a stand-alone sigma-delta modulator, constant-gm biasing circuit, oscillator and internal thermometer circuit. The CDS pre-amplifier has an adjustable gain and digitally programmable offset cancellation. The stand-alone sigma-delta modulator has a peak SNR and SNDR of 94 dB and 90 dB, respectively, at 25 degree C, and 94 dB and 87 dB at 300 degree C. The gain stability of the CDS pre-amplifier for GA = 6, 12 and 24 is 62, 66 and 95 ppm/degree C, respectively, for 25 degree C < T < 300 degree C. At 300 degree C, the modulator with CDS pre-amplifier achieves a dynamic range of 110 dB including the stand-alone modulator range.

Committee: Steven Garverick (Advisor); Mehran Mehregany (Other); Christian Zoraman (Other); Darrin Young (Other); Chung-Chiun Liu (Other) Subjects:

Master of Science, University of Akron, 2007, Mechanical Engineering

Shape memory alloys (SMAs) have been used as actuators in many different industries since the discovery of the shape memory effect. These include, but are not limited to, applications in the automobile industry, medical devices, commercial plumbing, and robotics. The use of SMAs as actuation devices in aeronautics has been limited due to the temperature constraints of commercially available materials. Consequently, work is being done at NASA's Glenn Research Center to develop new SMAs capable of being used in high temperature environments. One of the more promising high-temperature shape memory alloys (HTSMAs) is Ni19.5Ti50.5Pd25Pt5. Recent work has shown that this material is capable of being used in operating environments of up to 250°C. This material has also been shown to have very useful actuation capabilities, demonstrating repeatable strain recoveries up to 2.5% in the presence of an externally applied load. Based on these findings, further work has been initiated to explore potential applications and alternative forms of this alloy, such as springs. Thus, characterization of Ni19.5Ti50.5Pd25Pt5 springs, including their mechanical response (e.g. stroke capabilities, load carrying capabilities, and work outputs) and how variations in this response correlate to changes in geometric parameters (e. g. wire diameter, coil diameter, wire-to-coil diameter ratio, and number of coils) are discussed. The effects of loading history, or training, on spring behavior were also investigated. A comparison of the springs with wire actuators is made and the benefits of using one actuator form as opposed to the other discussed. These findings are used to discuss design considerations for a surge-control mechanism used in the centrifugal compressor of a T-700 helicopter engine. The mechanical response observed during testing is then compared with responses predicted using current SMA spring design methodology. The deficiencies in predictions using this current design methodology (open full item for complete abstract)

Committee: D. Quinn (Advisor) Subjects: Engineering, Aerospace

Doctor of Philosophy, Case Western Reserve University, 2024, Geological Sciences

Little is understood about the chemical evolution of banded iron formations (BIFs) subducted into the mantle during the Precambrian era. In general, the mantle becomes more reducing with increasing depth, with much of the deep mantle thought to be below the iron-wustite (IW) buffer. At equilibrium, under shallower mantle conditions, the hematite and magnetite in subducted BIFs would reduce wustite. In more deeply subducted BIFs, where the oxygen fugacity buffer is below IW, the wustite would reduce to iron metal. A key question is how rapidly iron oxide reduction reactions proceed at mantle pressures and temperatures. Fast reaction rate would imply that large amounts of wustite and/or metal may have precipitated in the deep mantle. BIFs that reduced to wustite and resisted further reduction could exist in the form of ULVZs (ulta-low velocity zones), as suggested by Dobson and Brodholt (2005). BIFs that fully reduced to iron metal could have produced large volume iron diapirs which would have been capable of sinking into the core and providing an inner core nucleation substrate, as suggested by Huguet et al. (2018). The studies reported here seek to answer these questions by determining the high-pressure, high-temperature reduction rates of iron oxides under mantle conditions. Chapter one describes the various approaches used to recreate banded iron formation subduction at high-pressures and high temperatures. Experiments explore temperatures from 600-1200 oC and pressures from 1.5-15 GPa. Chapter two addresses the first step of BIF reduction—the reduction of hematite and magnetite to wustite in the upper mantle. Experiments explore 14 temperatures from 600-1400 oC and pressures between 2-14 GPa. Chapter three addresses the final step in BIF reduction—the reduction of wustite to iron metal in the lower mantle.

Committee: James Van Orman (Advisor); Steven Hauck II (Committee Member); Alp Sehirlioglu (Committee Member); Beverly Saylor (Committee Member); Nathan Jacobson (Committee Member) Subjects: Experiments; Geochemistry; Geological; Geology

Doctor of Philosophy, Case Western Reserve University, 2024, EECS - Electrical Engineering

Next generation gas turbine engines will incorporate integrated microelectronic sensors designed to enhance aircraft functionality, engine efficiency, and safety by direct measurement of temperature, pressure, air flow and other parameters. Monitoring these parameters requires positioning sensors in the hot zone of the engine with temperatures in excess of 400°C. At these temperatures, small signal amplification is needed at the transducer to distinguish the desired signal from significant electronic noise generated by the engine. The most demanding applications are associated with locations that can only be accessed by wireless connections, necessitating the need for on-board amplifiers, oscillators, mixers and other radio frequency circuits that exhibit stable operation at high temperatures. To address this technology gap, a 50 MHz Class-A amplifier based on a high power silicon carbide static induction transistor (SiC SIT) and designed to operate at 400°C was 18 developed. The Class-A architecture was selected for its simple design and the SiC SIT was selected due to its potential for low power operation at high frequencies and high temperatures. The development of the amplifier involved: (1) characterization of a 4H-SiC SIT at temperatures up to 400°C, (2) development of a small signal model that emulates the performance of a 4H-SiC SIT for temperatures up to 400οC, (3) modeling-based design of a SiC SIT-based Class-A amplifier using the small-signal SiC SIT model, (4) development of capacitors, resistors and inductors for operation at 400°C and (5) fabrication of the Class-A amplifier and testing at 400°C. For an Ids of 40 mA, the SiC SIT exhibited a S21 gain of 9.35 dB at 400°C, only a ~ 40% reduction from room temperature. The transconductance was 60 mS at 400°C, which corresponds to a transition frequency of 270 MHz, well above the design frequency. For the amplifier, the S11 and S22 parameters showed desired ope (open full item for complete abstract)

Committee: Dr. Christian Zorman (Advisor) Subjects: Engineering

Master of Science, University of Akron, 2022, Geology

Stresses in the upper crust are redistributed to the lower crust after earthquakes. Stresses released by seismic slip induce crystal-plastic deformation in the mid to lower crust, which is composed of foliated, heterogeneous feldspathic rocks that deform and transfer stress back to the upper crust. Current models for the strength of the crust are primarily based on flow laws determined from experimentally deformed homogeneous quartzites or other monophase rocks. However, heterogeneities such as foliation orientations and foliation intensities, which are known to cause anisotropy of rock strength under brittle conditions, may cause viscous anisotropy at high temperatures and pressures where crystal-plastic mechanisms are dominant. To investigate if heterogeneities like foliation orientation and foliation intensity cause viscous anisotropy, I deformed weakly foliated Westerly Granite and strongly foliated Gneiss Minuti in different orientations that maximize (foliation at 45 degrees to the compression direction) and minimize (foliation parallel and foliation perpendicular to the compression direction) the shear stresses on the dispersed, elongate biotite grains in the quartz-feldspar framework, which should be the weakest and strongest orientations, respectively. These rocks were chosen because they both have similar low biotite contents (7%) and compositions: Westerly Granite is composed of 22 vol% quartz, 26 vol% K-feldspar, 45 vol% albite, and 7 vol% biotite and Gneiss Minuti is composed of 29 vol% quartz, 10 vol% K-feldspar, 53 vol% plagioclase and 7 vol% biotite. Experiments were performed using a Griggs apparatus at a temperature (T) of 800°C, confining pressure (Pc) of 1.5 GPa, and strain rate of 1.6 x 10-6/s. Westerly Granite and Gneiss Minuti reached peak stresses of 920 (+/- 50 MPa) and 670 (+/- 75 MPa), respectively, and viscous anisotropy was minor with anisotropy coefficients of 1.1x and 1.2x, respectively. Westerly Granite contained microstructures like (open full item for complete abstract)

Committee: Caleb Holyoke (Advisor); Molly Witter-Shelleman (Committee Member); John Peck (Committee Member) Subjects: Geology

Doctor of Philosophy, The Ohio State University, 2022, Welding Engineering

The automotive industry wants to advance integrated computational materials engineering (ICME) approaches that combine models of joining processes and microstructural evolution for prediction of material property gradients and ultimately the mechanical performance of multi-sheet lap joints. Despite the increasing demand for computational optimization within vehicle structures and the increased use of low-density materials, modern integrated modeling frameworks of automotive lap joining are often limited to the resistance spot welding (RSW) of conventional steels. Moreover, important phenomena in steel weldments, like decomposition of austenite on-cooling, tempering of martensite, and microstructure-dependent flow stress and damage properties are too material-specific for universal application. In this research, generalized metallurgical and mechanical modeling strategies are investigated for increased applicability to a wider range of steels and joining processes. The study evaluates: the reliability of heat transfer predictions within state-of-the-art numerical models of RSW, the accuracy of existing austenite decomposition models, the readiness of steel time-temperature-transformation (TTT) diagram tools containing CALPHAD-calculated parameters, the generality of a recently developed martensite tempering model, and the determination of RSW fusion and heat-affected zone flow stress and fracture behavior. Results show that state-of-the art finite element models of RSW that are validated using experimental weld nugget dimensions have a propensity to underpredict cooling rates. A JMAK and additivity rule approach calibrated with experimental TTT diagram data exhibited the greatest accuracy when predicting AHSS austenite decomposition; however, calibrations using calculated TTT diagrams better facilitated material optimization. Generalized parameters within a JMAK-type model of martensite tempering successfully predicted HAZ softening within martensitic and dual-phase (open full item for complete abstract)

Committee: Antonio Ramirez (Advisor); Avraham Benatar (Committee Member); Boian Alexandrov (Committee Member) Subjects: Materials Science

Master of Science in Mechanical Engineering (MSME), Wright State University, 2019, Mechanical Engineering

Current hypersonic vehicles tend to be incapable of producing onboard power with traditional generators due to their use of supersonic combusting ramjets (scramjets). Because of this, they seek additional energy sources for supporting advanced electronics or other auxiliary power-dependent devices while requiring elaborate thermal management systems to combat temperatures exceeding 700ºC. The incorporation of Solid Oxide Fuel Cell (SOFCs) stacks is an efficient solution, capable of generating large quantities of power through the use of natural fuel sources at high temperatures. Developments in this thesis include the design, construction, and support of a system operating at hypersonic-environment conditions with a usable micro-fuel cell. The capability of testing a stack of SOFCs at both elevated temperature and pressure conditions with various natural fuel sources has become a sought-after experiment by many energy production affiliates. Experimentation for this thesis focuses on the optimization of fluid and thermal inputs to work towards supporting successful testing of SOFCs in both single and stacked formations with variable input conditions. Evaluation of the system's operational parameters were defined and recommendations for continual enhancement of primary components are given. This research acts as a transition into future fuel-cell testing development by the Air Force Research Labs (AFRL) and all supporting parties. APPROVED FOR PUBLIC RELEASE, CASE NUMBER 88ABW-2019-3904.

Committee: Rory A. Roberts Ph.D. (Advisor); Mitch Wolff Ph.D. (Committee Member); Scott K. Thomas Ph.D. (Committee Member) Subjects: Aerospace Engineering; Engineering; Mechanical Engineering

PhD, University of Cincinnati, 2019, Engineering and Applied Science: Chemical Engineering

The water gas shift (WGS) reaction of syngas (mainly containing CO, CO2, and H2) and subsequent H2/CO2 separation are key operations for H2 production from fossil fuels, agricultural and forestry biomass, and municipal wastes with pre-combustion CO2 capture in thermal electric power production by the emerging integrated gasification-combined cycle (IGCC) power plants. Hydrogen permselective membrane reactors (MR) are capable of achieving near complete CO conversion (?CO) with simultaneous H2/CO2 separation that can substantially simplify and intensify the process to lower the overall operation cost. However, up to date, there is a lack of WGS MRs, which are practically viable either due to membrane instability in the WGS reaction of real syngas or insufficient ?CO and H2 recovery (RH2). This dissertation reports the development and scale up of thermally and chemically stable tubular zeolite membranes for future industrial high temperature and high pressure WGS MR to achieve nearly complete ?CO when nearly total RH2 is achieved in the permeate stream. An effective in-situ crystallization method has been established for synthesizing MFI-type zeolite membranes on industrially meaningful low-cost commercial porous a-alumina tube supports. The zeolite membranes with a length of 35 cm exhibited a H2/CO2 selectivity (aH2/CO2) ranging from 10 to 45 and hydrogen permeance (Pm,H2), of 1 – 2*10-7 mol/m2·Pa·s at 500oC. The WGS reaction in the single tube zeolite MR has been studied at high temperature (500oC) and high pressure (20bar) using nanocrystalline Fe-based catalysts under practically meaningful space velocities and steam-to-CO ratios. The zeolite membranes with moderate aH2/CO2 and Pm,H2, exceeded the equilibrium conversion at >500oC and achieved ?CO >99.9%. Realization of near-complete ?CO must rely on the prevention of excessive permeation of CO when the membrane has imperfect H2/CO selectivity. For the porous membranes with imperfect H2/CO permeation selecti (open full item for complete abstract)

Committee: Junhang Dong Ph.D. (Committee Chair); Joo-Youp Lee Ph.D. (Committee Member); Peter Panagiotis Smirniotis Ph.D. (Committee Member); Maobing Tu Ph.D. (Committee Member) Subjects: Chemical Engineering

Master of Science, The Ohio State University, 2014, Welding Engineering

High strength alloys, such as titanium alloys and steels have been widely used for armor applications. However, high strength materials have poor formability at room temperature and are prone to cracking during welding. It is necessary to develop alternative manufacturing methods that can replace conventional welding technologies. The main objectives of this project are: 1) development of a testing procedure for evaluation of the response of high strength alloys to hot induction bending, and 2) development of optimal process control windows for hot induction bending of three high strength materials: alloy Ti-6Al-4V and armor steels Armox 440 and ARL XXX. A testing procedure has been developed that combines hot ductility testing, high temperature straining using a GleebleTM thermo-mechanical simulator, high temperature straining followed by room temperature tensile testing, evaluation of response to tempering, phase transformation analysis, thermodynamic simulations, and metallurgical characterization. Hot ductility testing indicates a gradual increase in ductility of the three tested alloys as temperature increases. Strain rate has no significant effect on hot ductility of alloy Ti-6Al-4V and ARL XXX steel. During hot ductility testing, extensive void formation is observed in alloy Ti-6Al-4V between the starting temperatures of alpha and beta transformation and the recrystallization temperature, and in Armox 440 steel between the A1 and A3 temperatures. No voids were found above beta solvus temperature in Ti-6Al-4V and above the A3 temperature in Armox 440. Limited void formation occurs below the start of alpha and beta transformation in Ti-6Al-4V and below the A1 temperature in Armox 440. High temperature straining tests show that strain-induced porosity in Ti-6Al-4V can be avoided if strain is limited below 24% at 430 degrees Celsius and below 7% at 650 degrees Celsius. In Armox 440 and ARL XXX steels, voids were only observed in samples strained to failure. High (open full item for complete abstract)

Committee: John Lippold (Advisor); Boian Alexandrov (Committee Member); David Phillips (Committee Member) Subjects: Engineering; Metallurgy

Master of Science in Engineering, Youngstown State University, 2007, Department of Electrical and Computer Engineering

This research demonstrates several methods to produce high voltage Schottky contact diodes. How contact construction and process temperatures affect turn-on voltage Schottky barrier height, on-resistance, and reverse breakdown voltage are studied. The performance of varied contact terminal construction types and temperature processes used to fabricate Schottky diodes were evaluated. The diodes are constructed of nickel metal mechanical (pressure) contacts and plasma sputter deposited nickel metal contacts on silicon carbide (SiC). Current-voltage characterizations were used to study the differences in performance verses geometric construction types, sputter deposition temperature, and annealing temperatures. The configurations studied were needle points, spheres, and planar metal-semiconductor contacts varying in interface areas that ranged from 0.58*10-4 to 6.2*10-4 cm2. Planar Schottky contacts 500 μm in diameter sputter deposited at 27C and 600C are exposed to a range of temperatures in ultra pure nitrogen atmosphere. These Schottky contacts were studied to gain insight into mechanical contacts, plasma sputter deposited contacts, and temperature processes.

Committee: Frank Li (Advisor) Subjects:

MS, University of Cincinnati, 2011, Engineering and Applied Science: Mechanical Engineering

High density polyethylene (HDPE) is a common polymer material that is widely used in industrial applications. While significant amount of efforts have been devoted to understanding the constitutive behavior of HDPE, very little work has been performed to investigate the material response of HDPE at high strain rate and high temperature. The main objective of this research is to develop a constitutive model to bridge this gap by focusing on the non-linear stress-strain behavior in the high strain rate and high temperature range. A series of monotonic uniaxial compressive tests have been conducted at high temperature (100°C) and high strain rate (1/s) to characterize the HDPE behavior. Based on the experimental results, existing hyperelastic material models such as Mooney-Rivlin, Ogden, Arruda-Boyce, are assessed with the use of ABAQUS (a finite element software). Based on extensive comparisons, a new three-dimensional constitutive model for HDPE has been proposed. The constitutive equation integrates the basic mechanisms proposed by Boyce et al. [6] and Shepherd et al. [8]. The total stress is decomposed into an elastic-viscoplastic representation of the intermolecular resistance acting in parallel with a time and temperature dependent network resistance of polymer chains. Material constants involved in the model were calculated by fitting the compressive test results to the proposed constitutive equations. A constitutive solver for the proposed model has been developed. The stress-strain relation resolved from the constitutive model closely matches the corresponding ones from the experiments.

Committee: Dong Qian PhD (Committee Chair); Shepherd Shepherd PhD (Committee Member); Yijun Liu PhD (Committee Member) Subjects: Mechanical Engineering

Master of Science, The Ohio State University, 2012, Mechanical Engineering

In this study, gear contact tests were performed using a recently developed test methodology capable of both high-power (pitch-line velocities up to 50 m/s and pinion torques up to 450 N-m) and high-temperature (oil inlet temperatures up to 150C) operating conditions. Test specimens and operating conditions were chosen in order to simulate high-power automotive and aerospace applications. Automotive test specimens were made from a typical automotive transmission gear steel, SAE 4118M, at surface roughnesses typical of hard ground gears. Aerospace test specimens were made out of a high performance (high-temperature) proprietary gear steel. These aerospace specimens were either chemically polished or super-finished following grinding to achieve roughness amplitudes more than 10 times smoother than typical ground surfaces. Throughout each test interim inspections were used to identify and monitor failure modes. Experimental testing for automotive applications is shown to consistently produce contact fatigue failures in the form of micro-pitting and macro-pitting. Tests were suspended when macro-pits exceeded the test methodologies pre-determined failure criteria. Experimental testing for aerospace applications is shown to be absent of any contact fatigue failures due to the extremely smooth contact surfaces. The primary mode of contact failure in aerospace tests is observed to be scuffing.

Committee: Ahmet Kahraman (Advisor); Gary Kinzel (Committee Member) Subjects: Aerospace Engineering; Aerospace Materials; Automotive Engineering; Automotive Materials; Engineering; Mechanical Engineering

Master of Science, The Ohio State University, 2011, Mechanical Engineering

Contact fatigue failures in the form of pitting or micro-pitting have been a perennial problem in power transmission applications. These failures are dictated by a large number of parameters including loading conditions, gear geometry and tooth modifications, kinematics (rolling and sliding velocities), lubricant parameters (viscosity, pressure-viscosity behavior), and material parameters (material type, hardness, case depth, residual stresses). As such, theoretical treatment of contact fatigue failures has been rather challenging, directing the focus to the experimental investigation of the problem. Most of the experimental gear pitting studies to date were limited to low-speed and low-temperature operating conditions. This study aims at developing a methodology for evaluating the contact fatigue lives of gears under high-speed (pitch-line velocities up to 50 m/s), high-stress (contact stresses up to 2 GPa) and high-temperature (oil inlet temperatures up to 150C). Specifications of a test machine concept that meets these requirements are defined and two test machines are designed and procured for this purpose. Gear test specimens that result in pits consistently are developed with the other competing failures (wear, scuffing, tooth breakage), as well as the high vibration conditions, avoided. Preliminary high-speed tests are presented at the end, representing both automotive and aerospace conditions to show that pitting and micro-pitting failures can be produced with the proposed methodology.

Committee: Ahmet Kahraman PhD (Advisor); Carlos Castro PhD (Committee Member) Subjects: Engineering; Mechanical Engineering

Master of Science, The Ohio State University, 2011, Geological Sciences

The viscosity of water is a first-order constraint on the transport of material from a subducting plate to the mantle wedge. The viscosity of fluids that are released during the dehydration of hydrous minerals during subduction can vary by more than 9 orders of magnitude between the limits of pure liquid water and silicate melts. Accurate determination of low viscosities (<1 mPa·s) for liquids at simultaneous high pressures (>1 GPa) and high temperatures (>373 K) is hindered by the geometry and sample size of high-pressure devices. Here the viscosity of water at pressures representative of the deep crust and upper mantle through use of Brownian motion in the hydrothermal diamond anvil cell (HDAC) is reported. By tracking the Brownian motion of 2.8 and 3.1 micron polystyrene spheres suspended in H2O, the viscosity of the water at high pressure and high temperature can be determined in situ using Einstein's relation. Accuracies of 3-10% are achieved and measurements are extended to pressures relevant to fluid release from subducting slabs and temperatures up to 150% of the melting temperature. Unhampered by wall effects of previous methods, the results from this study are consistent with a homologous temperature dependence of water viscosity in which the viscosity is a function of the ratio of the temperature to the melting temperature at a given pressure. Based on the homologous temperature dependence of water, transport times for fluids released from subducted plates inferred from geochemical proxies are too short for transport via porous flow alone, and suggest transport through a combination of channel-flow and porous flow implying hydrofracturing at 50-150 km depth.

Committee: Wendy Panero (Advisor); Michael Barton (Committee Member); David Cole (Committee Member) Subjects: Geophysics

Master of Science (MS), Ohio University, 2005, Chemical Engineering (Engineering)

The present study has been conducted to find the corrosion mechanisms and rates of an AISI 1018 steel in the presence of CO 2 and trace amounts of H 2 S using classical electrochemical techniques. The results obtained from experiments using electrochemical impedance spectroscopy measurements were theoretically analyzed by a semi-mechanistic model to reveal the conditions on the surface of the specimen used in the experiment. The experiments were designed to see the effect of different saturation values of iron carbonate and iron sulfide in the bulk solution on the corrosion rate of the sample. The experiments were conducted in a large scale (1000 lit) hastelloy flow loop at a fixed temperature of 60°C and total pressure of 7.9 bar. All experimental conditions were monitored regularly for the duration of the experiment. It was observed that the presence of trace amounts of H 2 S in the system decreased the corrosion rate significantly over time under the specific experimental conditions studied. This was due to the formation of an iron carbonate scale or iron sulfide scale, or both, which acted as a barrier to the diffusion of the corrosive species to the surface of the metal, thus decreasing corrosion rate.

Committee: Srdjan Nesic (Advisor) Subjects:

Master of Sciences, Case Western Reserve University, 2010, EMC - Mechanical Engineering

Acetone tracer-LIF in the gas phase is a widely used laser diagnostic technique in low to intermediate temperature and pressure combustion systems. In this work, we design, characterize, and validate a flexible static and flow system to study the independent and coupled effect of elevated pressure and temperature on the photophysics of acetone more relevant to practical engine like conditions (0.5 atm< P <40atm, 295K< T <700K) for an excitation wavelength of 282nm in nitrogen and air. It is shown that relative fluorescence increases for all pressures at elevated temperatures up to a maximum isotherm of ~425K; for subsequently higher temperatures, acetone fluorescence decreases. Acetone fluorescence is only moderately quenched in the presence of oxygen. The current work offers insight into the competing vibrational energy decay rates at elevated temperature and pressure and proposes a global re-optimization of model parameters from the original photophysical model developed by Thurber (1999).

Committee: Chih-Jen Sung PhD (Committee Chair); Yasuhiro Kamotani PhD (Committee Member); Gaurav Mittal PhD (Committee Member) Subjects: Aerospace Materials; Engineering; Mechanical Engineering

Master of Science (M.S.), University of Dayton, 2024, Mechanical Engineering

Supercritical carbon dioxide (sCO2) power cycles offer significant advantages in thermal efficiency, component flexibility, and adaptability to various heat sources. This study develops computational functions and multi-objective evolutionary optimization tools to enhance the performance of sCO2 power cycles, specifically targeting applications with finite thermal reservoirs. Leveraging the unique properties of sCO2, including its high density and excellent heat transfer capabilities, the research aims to optimize cycle efficiency, reduce component mass, and manage operational constraints. The research focuses on four primary sCO2 Brayton cycle configurations: Direct Heating – Recuperated Cycle (DH-RC), Direct Heating – Non-Recuperated Cycle (DH-NRC), Indirect Heating – Recuperated Cycle (IH-RC), and Indirect Heating – Non-Recuperated Cycle (IH-NRC). Each cycle is analyzed for its thermodynamic performance, component interactions, and potential for efficiency improvements. The simulation functions developed for these cycles incorporate iterative processes to ensure steady-state conditions and accurate energy conservation. Key to the optimization process are machine learning models and genetic algorithms, which handle the high-dimensional data and complex design criteria associated with sCO2 cycles. The NSGA-II algorithm is employed for multi-objective optimization, focusing on maximizing cycle efficiency and minimizing the mass of the turbine and compressor. This approach allows for the generation of Pareto-optimal solutions, providing a diverse set of optimal design configurations. The study also addresses the critical components of sCO2 cycles, including compressors, turbines, and heat exchangers. Detailed simulations and regression models are developed to predict the performance and mass of these components. The optimization framework integrates these models, allowing for comprehensive analysis and design refinement. For example, the heat exchanger models util (open full item for complete abstract)

Committee: Andrew Schrader (Advisor); Justin DelMar (Committee Member); Robert Lowe (Committee Member) Subjects: Mechanical Engineering

Master of Science, The Ohio State University, 2024, Welding Engineering

As Additively Manufactured (AM) refractory alloys are developed for extreme temperature environments, new methodologies evaluating their fitness for service must be developed. AM processes alter the properties and behavior versus wrought counterparts, and as much of the refractory alloy development ended decades ago, the adaptation of AM to refractory alloys introduces new challenges. Because refractory alloys are desirable for their high strengths at very high temperatures, they must be tested at these temperatures. A Gleeble 3800 thermomechanical simulator was modified and used to evaluate mechanical properties and oxidation of AM refractory alloys at their expected service temperatures, ranging from room temperature to thousands of degrees Celsius. Both the fixturing and sample's geometry for this new test were designed considering the joule heating utilized by the testing system as well as the potential risk of damaging standard components inside the test chamber. Oxidation during testing was manipulated by controlling the vacuum in the chamber and utilizing argon backfills. AM C103, TZM, and tungsten samples were built based on the designs created for this research and were tensile tested up to ultra-high temperatures. Mechanical properties were evaluated with the measurement of ultimate tensile strengths (UTS), yield strengths (YS), elongation, and strain-hardening coefficient as a function of temperature. C103 was the highest performing material, with an average UTS of ~650 MPa and over 25% elongation at room temperature. Strength at 500 °C - 1000°C showed similar behavior, but the strength from 1200 °C -1400 °C rapidly declined, and YS and UTS values were identical. Fractography analysis of the fracture surface indicated ductile fracture for the C103, while brittle fracture was observed in TZM and tungsten. Electron Backscatter Diffraction (EBSD) maps and pole figures of the C103 samples enabled the evaluation of the microstructures at the transition section (open full item for complete abstract)

Committee: Boian Alexandrov (Committee Member); Antonio Ramirez (Advisor) Subjects: Engineering; Materials Science; Mechanical Engineering

Doctor of Philosophy (PhD), Ohio University, 2024, Chemical Engineering (Engineering and Technology)

Oil refineries must adapt to unfamiliar crude oil chemistries originating from modern unconventional oil resources. Additionally, they face statutory requirements to co-process acidic bio-oils with ordinary crude oils. This results in exotic crude chemistries which can aggravate concerns for naphthenic acid and sulfidation corrosion related failures, amongst other processing challenges. Therefore, a reliable corrosion prediction tool becomes indispensable for oil refineries to ensure the safety and integrity of processing/distillation units while refining these unconventional oils. For the construction of such a corrosion prediction model, the reaction mechanisms of both naphthenic acid and sulfidation corrosion are further deciphered in this dissertation research. Associated kinetic equations are modeled to calculate the rates of the proposed elementary steps. These elementary rate equations are combined using mass conservation principles to obtain equations for overall corrosion rates. The derived corrosion rate equations capture the trends of experimental corrosion rates with respect to time, temperature, and concentrations of corrosive species. The phenomenological coefficients of the kinetic equations are derived from experimental and literature data. A computer program consisting of the derived kinetic equations has been built for the prediction of refinery corrosion. Simulations of the corrosion rates with respect to system parameters have been demonstrated.

Committee: David Young (Advisor); Srdjan Nesic (Committee Member); Eric Stinaff (Committee Member); Gheorghe Bota (Committee Member); David Drabold (Committee Member); Marc Singer (Committee Member) Subjects: Chemical Engineering; Materials Science; Molecular Chemistry; Petroleum Engineering; Physical Chemistry