Master of Science, University of Akron, 2024, Geology

Partial melting of hydrous phases such as amphibole, biotite, and muscovite occurs in orogens where distributed ductile thinning is causing exhumation of mid- to lower-crustal rocks. The partial melting of these hydrous phases contributes significantly to the physical and chemical evolution of the crust, as well as affecting the crust's strength. The Si-rich melts generated from partial melting reactions of mid- to lower-crustal assemblages migrate toward the upper crust leaving a more mafic restite. Previous laboratory experiments conducted on amphibole-, biotite-, or muscovite-bearing rocks performed at rapid strain rates (10-4/s to 10-5/s) result in brittle deformation due to high local pore pressures. These rapid experiments suggest this brittle behavior is the likely mechanism causing melt segregation in the crust. However, field evidence and slower strain rate experiments (10-6/s to 10-7/s) suggest that crystal plastic processes may be dominant during syndeformational partial melting. To investigate grain-scale melt segregation mechanisms in a common lower crustal protolith, I performed a suite of axial compression and general shear experiments on an amphibole-bearing source rock during syndeformational partial melting at T = 800-975°C, Pc = 1.5 GPa, at a strain rate (ε) of 1.6 x 10-6/s. I also performed axial compression experiments on a biotite-bearing gneiss and a muscovite-bearing quartzite at T = 950°C, Pc = 1.5 GPa, at a strain rate (ε) of 1.6 x 10-6/s to compare the differences in melt development depending on which hydrous phase is partially melting. The Nemo Amphibolite (d = 140 ± 85 μm) is composed of 62 vol% amphibole (Fe-hornblende), 27 vol% plagioclase (andesine; An30Ab69Or1), 8 vol% quartz, and 3 vol% titanite. The biotite-bearing gneiss (d = 80 +/- 40 microns) consists of quartz (43 vol%), plagioclase (andesine (An22Ab77Or1); 40 vol%), biotite (16 vol%), and ~1 vol% muscovite/Fe-Ti oxides. The muscovite-bearing quartzite is composed of 90 vol% q (open full item for complete abstract)

Committee: Caleb Holyoke (Advisor); Molly Witter-Shelleman (Committee Member); David Steer (Committee Member) Subjects: Earth; Experiments; Geochemistry; Geological; Geology; Mineralogy; Petrology; Plate Tectonics

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, Case Western Reserve University, 2021, Macromolecular Science and Engineering

This study focused on the investigation of electromechanical deformation and failure of monolithic and multilayered polymeric films when subjected to an instantaneous voltage using a needle-plane electrode setup. The first and the second chapters concentrated on the electromechanical deformation on monolithic films, including polycarbonate (PC), poly (vinylidene fluoride (PVDF), polystyrene (PS), polypropylene (PP) and high-density polyethylene (HDPE). The third chapter focused on the effect of layer thickness on the electromechanical deformation of PC/PVDF multilayered films. The strong effect of scaling, layer thickness, was elucidated on the complex damage mechanisms. In Chapter One, electrically induced mechanical stress was applied on monolithic PC films. Three different experimental methods were used to investigate the electrically induced mechanical deformation on the glassy PC film, namely, morphological observation, energy loss analysis, and dielectric hysteresis. The PC film exhibited reversible elastic behavior at electric field below 200 MV/m, showing no indentation on the film surface. When the field was above 200 MV/m, an irreversible spherical indentation was created at the needle tip. Subsequent thermal annealing of the deformed film revealed a recoverable “delayed elastic” and an irreversible “plastic” deformation. A three-stage mechanism was proposed based on these experimental results, which includes the correlation between the energy loss and the deformed volume. Chapter Two investigated the electromechanical deformation on other polymers and compared with PC. The additional amorphous materials, PS, and two semi-crystalline materials, HDPE and PP, having dielectric constants all around 2.5, exhibited a similar onset of observable deformation. However, PVDF, having a dielectric constant of 12.0, showed an onset at very low electric field. The depth and diameter of the deformation for all polymers increased with increasing electric field. Th (open full item for complete abstract)

Committee: Eric Baer (Committee Chair); Lei Zhu (Committee Member); Gary Wnek (Committee Member); Ya-Ting Liao (Committee Member) Subjects: Materials Science; Plastics; Polymers

Doctor of Philosophy, University of Akron, 0, Biomedical Engineering

The tricuspid valve, which is located on the right side of the heart, prevents blood backflow from the right ventricle to the right atrium. Regurgitation in this valve occurs when its leaflets do not close normally. Tricuspid valve regurgitation is one of the most common tricuspid valve dysfunctions, often requiring valve repair or replacement. The long-term success rate of the repair surgeries has not been promising; in many cases, reoperations are required within a few years after the first surgery. A limiting factor in understanding the etiology of tricuspid valve repair failure is our lack of knowledge regarding tricuspid valve biomechanics. In particular, tricuspid valve mechanical behavior has not been accurately studied. In addition, there is no precise analytical and/or computerized model to predict the mechanical responses of the valve under normal and pathological conditions. In the current study, we have used biaxial tensile testing, small angle light scattering, ex-vivo passive heart beating simulation, and sonomicrometry techniques to quantify the mechanical characteristics, microstructure, dynamic deformations, and geometric parameters of the tricuspid valve. We aimed to develop a more accurate computerized model of the tricuspid valve for simulation purposes. Our studies are important both for understanding the normal valvular function as well as for development/improvement of surgical procedures and medical devices.

Committee: Rouzbeh Amini Dr. (Advisor); Brian Davis Dr. (Committee Member); Ge Zhang Dr. (Committee Member); Francis Loth Dr. (Committee Member); Rolando Ramirez Dr. (Committee Member) Subjects: Anatomy and Physiology; Biomechanics; Biomedical Engineering; Biomedical Research; Engineering; Surgery; Technology

Master of Science (MS), Bowling Green State University, 2017, Geology

The length of a day on Earth (abbreviated LOD) is not exactly 24 hours. There is a small excess LOD that varies on timescales ranging from a few days to thousands of years, generally on the order of milliseconds. One characteristic of LOD variations is a sinusoidal component with a period of ~6 years. The cause of the ~6-year signal is unknown, but is generally suspected to be exchanges of angular momentum between the mantle and the core. This study aimed to test the hypothesis that the ~6-year LOD signal is due to coupling between the mantle and fluid outer core. The flow of the core's fluid deforms the base of the mantle, leading to redistribution of Earth's mass (causing changes in the gravitational field) and deformation of the overlying crust. Surface deformation data from a global network of high-precision Global Positioning System (GPS) stations was analyzed, and the component that acts on the ~6-year timescale was isolated and inverted for the core's flow. Resulting angular momentum changes were computed for the outer core and compared to the LOD signal to search for evidence of core-mantle coupling. Outer core angular momentum changes obtained from GPS deformation data exhibit evidence of the suspected core-mantle coupling, but this result is sensitive to inversion parameters. Changes in the gravitational field were also modeled and found to be smaller than the errors in the currently available data.

Committee: Yuning Fu PhD (Advisor); Richard Gross PhD (Committee Member); Marco Nardone PhD (Committee Member); Margaret Yacobucci PhD (Committee Member) Subjects: Geology; Geophysics

Master of Science, University of Akron, 2017, Geology

A Griggs rig apparatus was used to perform a number of strain rate stepping and pressure stepping experiments of O+ oriented synthetic quartz crystals. These samples were annealed at 1 atm and 900°C for 24 hours to convert the gel type water inclusions to free water inclusions similar to those that are found in natural milky quartz. Strain rate stepping experiments were performed at temperatures from 1000°C to 750°C, and strain rates from 1.6 X 10-4 s-1 to 1.6 X 10-6s-1, while confining pressure was held constant at 1.5 GPa. These samples were observed to yield over a range of <10 to ~300 MPa in many cases, though under some of the conditions tested samples did not yield. Two pressure stepping experiments were performed, one at 800°C and one at 750°C, with a strain rate of 1.6 X 10-6s-1 and confining pressures between 0.6 GPa and 1.5 GPa. The sample strengths measured in the pressure stepping experiments were between ~30 MPa and ~60 MPa. Microstructures observed within deformed samples include undulatory extinction and deformation lamellae. The mechanical data from those experiments that were consistent with dislocation creep fit the flow law: ε′=0.00177*CH2O1.9*fH2O* ςdiff3.29* e(-268.6/(R*T)) Under natural conditions, this suggests plastic yielding of quartz occurs at ~9 km (~225°C) deep in the crust.

Committee: Caleb Holyoke III (Advisor); LaVerne Friberg (Committee Member); John Peck (Committee Member) Subjects: Geology; Geophysical; Geophysics

Master of Science in Engineering (MSEgr), Wright State University, 2015, Mechanical Engineering

The ability to design vehicles capable of reaching hypersonic speeds has become a necessity to satisfy industry requirements, hence requiring the need for better understanding of creep behavior of materials. Although the steady state creep of metals has been analyzed rigorously, there is little known about transient creep of many metals. Understanding transient creep behavior of metals is crucial in analysis and design of short term hypersonic flight applications. Hence, a transient creep analysis of 304SS, Al7075-T6, Al2024-T6, Inconel 625, Inconel 718, and Rene N4 is carried out focusing on the microstructural behavior of these metals undergoing high temperature operating conditions. In doing so, the material properties that were unknown in literature were determined by parameter fitting techniques using existing steady state experimental data and also previous parametric studies determining critical parameters affecting strain values. A transient creep deformation map for each metal is produced including the required design space of the application.

Committee: Mitch Wolff Ph.D. (Committee Chair); Anthony Palazotto Ph.D. (Advisor); Amir Farajian Ph.D. (Committee Member) Subjects: Aerospace Engineering; Aerospace Materials; Engineering; Materials Science; Mechanical Engineering

Master of Science, University of Akron, 2014, Mechanical Engineering

Numerical analysis for a two dimensional case of two–phase fluid flow has been performed to investigate the impact, deformation of droplets and filament for printing processes. The purpose of this investigation is to study the phenomenon of liquid droplet and filament impact on a rigid substrate, during various manufacturing processes such as jetting technology, inkjet printing and direct printing. This investigation focuses on the analysis of interface capturing and the change of shape for droplets (jetting technology) and filaments (direct printing) being dispensed during the processes. Investigations have been performed with an adaptive quadtree spatial discretization with geometrical Volume–Of–Fluid (VOF) interface representation, continuum–surface–force surface tension formulation and height-function curvature estimation for interface capturing during the impact and deformation of droplets and filaments. Gerris Flow Solver, an open source finite volume code, has been used for the numerical analysis which uses a quadtree based adaptive mesh refinement for two–dimensional analysis. The numerical model has been validated with literature and experiment. The investigation has been performed for ranges of dimensionless governing parameters.

Committee: Jae-Won Choi Dr. (Advisor); Abhilash Chandy Dr. (Committee Member); Chang Ye Dr. (Committee Member) Subjects: Engineering; Fluid Dynamics; Mechanical Engineering

Master of Science, The Ohio State University, 2010, Geological Sciences

The Andean foreland of central-western Argentina (30°-35°S) is characterized by the interaction of the east-vergent, thick-skinned Sierras Pampeanas and the west-vergent, thin-skinned Precordillera. Blind thrust faults are associated with the transition between these structural provinces, and large earthquakes have resulted from their interplay beneath the cities of Mendoza and San Juan. This study develops and applies a geomorphic approach to reveal buried tectonic features at both the scale of individual structures and the regional-scale. We interpret changes in bank heights and sinuosity from three rivers located between the Cerro Salinas and Montecito anticlines to suggest the existence of a third, buried structure. Inflections in elevation swaths indicate these three structures may be connected by the southern continuation of the Cerro Salinas thrust, which would tie the three to the Sierras Pampeanas structural province. Regional-scale drainage in the Andean foreland shows that neither current- nor paleorivers have flowed across the Alto del Desaguadero area. Inflections in W-E and N-S elevation swaths across this area suggest the influence of tectonic forcing, possibly due to a rising basement structure similar to the Sierra Pie de Palo to the north.

Committee: Dr. Lindsay Schoenbohm (Advisor); Dr. Ian Howat (Committee Member); Dr. Lawrence Krissek (Committee Member) Subjects: Geology

Master of Science (MS), Bowling Green State University, 2009, Geology

Quartz-rich aggregates provide a good analog for Earth's upper crust. Previous workers have shown the presence of water can greatly decrease the strength of quartz and can shift the brittle-ductile transition conditions to lower temperatures/pressures for quartz-rich rocks in the Earth. In this study, a combination of Fourier Transform Infrared Spectrometry, optical light microscopy, Scanning Electron Microscopy, and Cathodoluminescence Microscopy analyses were used to determine the distribution and transport of water and water-related species within natural quartz aggregates using dehydration, rehydration, and isotope exchange experiments. Water within natural quartz arenites is distributed along grain boundaries, at grain junctions, and within the grain interiors. Fluid inclusions trapped along healed microfractures are the main source of molecular water within the grains. The concentration of water within the quartz arenite samples is proportional to the amount of deformation and type of deformation-related microstructures present. At brittle-ductile transition conditions (between 150 degrees C and 300 degrees C), water transport appears to be influenced by both brittle and ductile factors. Water is transported by oxygen volume diffusion, oxygen grain boundary diffusion, and as molecular water along microfractures within natural quartz arenites. Microfracture-assisted transport may play an important role in the transport of water throughout natural quartz arenites around the brittle-ductile transition conditions.

Committee: Dr. John Farver (Advisor); Dr. Charles Onasch (Committee Member); Dr. Sheila Roberts (Committee Member) Subjects: Geology

Master of Science, The Ohio State University, 2005, Graduate School

Committee: Not Provided (Other) Subjects:

Master of Science, Miami University, 2024, Mechanical and Manufacturing Engineering

Lattice structures are celebrated for their lightweight characteristics and superior mechanical performance. In this research, a strut reinforcement technique was employed to enhance the energy absorption capacities of 3D re-entrant auxetic (Aux), hexagonal (Hex), and hybrid Auxetic-Hexagonal (AuxHex) lattice structures. The investigation involved finite element analysis to delve into the mechanical and energy absorption properties of these novel designs during quasi-static compression testing. The results from the uniaxial compression tests of the reinforced designs were then compared with those from traditional 3D hexagonal and re-entrant auxetic lattice structures. To accurately simulate the mechanical behavior of the 3D printed lattice structures, the mechanical properties of the PA2200 matrix material—manufactured via additive manufacturing—were utilized. The outcomes indicated by the stress-strain and energy absorption curves suggest that these newly proposed designs are optimal for applications requiring high energy absorption at large strains. Thus, these findings pave the way for developing novel designs in 3D hexagonal and re-entrant auxetic lattice structures, which are poised to offer enhanced mechanical strength and exceptional specific energy absorption properties. Expanding on these insights, future research could explore further variations in lattice geometry and reinforcement methods to optimize the performance of these structures under different loading conditions.

Committee: Muhammad Jahan (Advisor); Carter Hamilton (Committee Member); Jinjuan She (Committee Member); Jeff Ma (Advisor) Subjects: Biomechanics; Experiments; Materials Science; Mechanical Engineering; Mechanics

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

Ultrasonic vibration has widely been studied for potential in the metal forming industry for its ability to temporarily soften the material. The lack of understanding of the underlying mechanisms of ultrasonic softening and difficulty in scaling to industrial applications has limited its use. To better understand the fundamentals to the softening mechanism, ultrasonic-assisted (UA) micro-tensile tests of low-carbon steel, aluminum alloy 2219 varying grain size, and titanium grades 2 & 5 are conducted in this study. The ultrasonic vibration is oriented along the tensile axis, and the ultrasonic amplitude is uniform in micro-dogbone specimen. Acoustic softening is observed, increasing with ultrasonic amplitude for all materials. Further investigation on the unique residual effect after ultrasonic treatment based on the microstructure is conducted. Low-carbon steel exhibited residual softening increasing with ultrasonic amplitude. EBSD analysis was conducted on the steel samples strained to 10% strain to explain the reduction of strain hardening during UA and residual softening after UA. Two ultrasonic amplitude levels were compared along with a control NoUA case. Higher LAGB fractions were observed with increasing ultrasonic amplitude, attributed to enhanced dislocation motion resulting in dipole annihilation and subgrain formation. Lower amplitudes assisted in lattice rotation with minor change in the microstructure while higher amplitudes resulted in significant intragranular deformation. Aluminum alloy 2219 was friction stir processed to achieve a refined microstructure and compared to a Al2219-T4 temper with a larger grain size. The resultant reduction of flow stress from ultrasound with varying grain size was similar, however, residual hardening was observed in the T4 temper, while no residual effect was observed in the refined microstructure. Also, the ultimate tensile stress and elongation improved after ultrasonic treatment in the T4-temper. With the (open full item for complete abstract)

Committee: Xun Liu (Advisor); Avraham Benatar (Committee Member) Subjects: Materials Science; Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2024, Materials Science and Engineering

Shear deformations in metallic materials, whether carried by dislocations, mechanical twinning, martensitic transformations in crystalline solids, or shear transformation zones (STZs) in amorphous solids, exhibit several common characteristics. These include autocatalysis driven by long-range elastic interactions and the occurrence of strain avalanches post-yielding. Therefore, to achieve controlled strain release and desired stress-strain behaviors tailored to specific applications, it is imperative to mitigate autocatalysis. In this dissertation, we elucidate strategies to mitigate autocatalysis by focusing on three commonly used metallic materials: Al alloys, extensively employed as lightweight structural materials in manufacturing; NiTi shape memory alloys (SMAs), widely utilized in aerospace, automotive, and biomedical industries; and metallic glasses, utilized in precise instruments and biomedical devices. The primary aim is to employ various computational methods to investigate mechanisms for suppressing autocatalysis and attaining desired mechanical responses in these three examples through appropriate microstructure engineering. In Al-alloys, dislocations are the primary carriers of shear deformation and various precipitate microstructures have been strategically designed to regulate the dislocation activities. In particular, in 7xxx series Al-alloys, e.g., Al-Zn-Mg-Cu, η' phase is the commonly observed shearable precipitate phase to strengthen the alloys. By adding Mn and Si, non-shearable precipitates (Al6Mn and α) have been introduced to prevent stain localization. To understand the synergy between the two types (shearable and non-shearable) of precipitates in achieving desired combinations of strength and ductility, it is necessary to investigate the possible interactions between the two during precipitation. These interactions determine the precipitate microstructures, as well as the interactions between a given precipitate microstructure and dislocat (open full item for complete abstract)

Committee: Yunzhi Wang (Advisor); Steve Niezgoda (Committee Member); Michael Mills (Committee Member) Subjects: Materials Science

Doctor of Philosophy, The Ohio State University, 2024, Aerospace Engineering

Fluid-Structure Interactions (FSI) are a quintessential multi-disciplinary challenge, where the flowfield is influenced by the structure, and structural deformation is induced by the flow pressure. Computational and experimental research thrusts often seek to answer specific problems for specific configurations, offering observational answers to relatively complex problems. While there is a large body of work on FSI as a whole, the specific coupling mechanisms between the fluid and structural surface in the context of turbulent boundary layers (TBLs) in supersonic flows is an under-explored area of study. This dissertation details progress addressing this gap through cooperative consideration of high-fidelity simulations, classical semi-empirical models, analysis of the governing equations, and data-driven models. Large-Eddy Simulations (LES) of TBLs with static deformations are compared against classical semi-empirical models to characterize applicability to statically deformed surfaces for predicting loads transmitted from the boundary layer to the structure. Additionally, analysis of the governing equations, in conjunction with data-driven modeling, is used to extract a coherent link between structural deformation and the onset of local flow separations. Finally, a parametric study is carried out using Reynolds-Average Navier-Stokes (RANS) and Kriging surrogates to assess the impact of statically deformed surfaces on a downstream ramp. LES indicates that for a variety of deformations sized on the order of the incoming boundary layer, localized flow separation can develop. This leads to important flow modifications that are not readily captured with low-fidelity or semi-empirical models. Motivated by this, a first-order link between local flow separation and structural deformation parameters is established using the Momentum Integral Equation (MIE) combined with data-driven analysis. The curvature of the surface is identified as the dominant structural param (open full item for complete abstract)

Committee: Jack McNamara (Advisor); Datta Gaitonde (Advisor); Scott Peltier (Committee Member); Jen-Ping Chen (Committee Member); Lian Duan (Committee Member) Subjects: Aerospace Engineering

Doctor of Philosophy, University of Akron, 2024, Mechanical Engineering

Processing-related defects such as porosity, residual stress, and surface roughness are the primary impediments to the widespread adoption of additive manufacturing in high-performance aerospace structures, primarily in applications where fatigue is an area of concern. Strengthening the surface through an emerging surface treatment approach has the potential to mitigate these defects and subsequently improve the surface quality, as well as increase the fatigue strength of the additively manufactured components. The core objective of this research work was to employ a severe surface plastic deformation (SSPD) process to improve the surface and fatigue properties of additively manufactured Ti-6Al-4V alloys with a particular emphasis on directed energy deposition (DED) re-paired and fully produced electron beam powder bed fusion (EB-PBF), via combination of laser heating (LA) and ultrasonic nanocrystal surface modification (UNSM). Laser heating plus ultrasonic nanocrystal surface modification is an innovative mechanical sur-face treatment tool, and it has been demonstrated as an interesting laser-based mechanical surface treatment technology to induce thicker deformation layer on the surface using low energy input, impact load, low amplitude, and high ultrasonic frequency, leading to enhancement of the microstructure features, surface strength, and resultant mechanical properties of metallic materials. Physical and mechanical characteristics changes in target materials were investigated using optical (OM) and scanning electron microscopy (SEM), X-ray diffraction (XRD), profilometry, and a hardness tester. The results revealed that the proper thermal and impact energies of the applied surface treatment was effective in inducing higher plasticity flow and promoted greater surface grain refinement. Strengthening of metallic alloys through grain refinement is evidenced by achieving maximum strength, a phenomenon referred to as the Hall-Perch principle. In particular, the s (open full item for complete abstract)

Committee: Gregory Morscher (Advisor); Yalin Dong (Committee Member); Jun Ye (Committee Member); Wieslaw Binienda (Committee Member); Manigandan Kannan (Committee Member) Subjects: Aerospace Materials; Materials Science; Mechanical Engineering

Doctor of Philosophy, Case Western Reserve University, 2024, Macromolecular Science and Engineering

Traditionally, extrinsic approaches (e.g. blending and using additives) have been used to enhance the mechanical properties (e.g. toughness) of commercially available semicrystalline thermoplastics. In a continual search for economically scalable, scrapless, simple, and versatile manufacturing approaches, novel solid-state processes have a unique advantage over melt-processing methods alone. Cold-roll milling, or plastically deforming a workpiece by passing it through two counter-rotating rollers below its primary softening temperature, is well-established in the production of ductile metals. Roll-milling not only reduces thickness, but also cold-works the material improving its strength through microstructural refinement. In polymers, a crystalline network structure develops. The focus of this work is on biaxial cold-rolling (cross-rolling) which involves cross-passes alternately 90 ° apart, resulting in a sheet with planar isotropy. In the first part of this dissertation (chapter 2), the deformation of HDPE by cross-rolling is studied. Enhanced barrier properties (measured by oxygen permeability analyzer), increased visible light transmission (measured by spectrophotometer), and increased tensile fracture strength were observed after cross-rolling. A connection to discontinuous change in crystalline structure with thickness reduction (i.e. lamellar fragmentation) detected by density measurement, thermal analysis, and small-angle x-ray scattering (SAXS) is discussed. The second portion (chapters 3-5) focuses on the cross-roll pre-deformation of semicrystalline polymers below both the Tm and Tg at room temperature, and subsequently annealing at temperatures both below and above the Tg. In chapter 3, the Izod impact toughness of poly(p-phenylene sulfide), a notoriously low toughness high-temperature engineering thermoplastic, is found to increase by a factor of 10 after cross-rolling. The elongation to failure is enhanced by a factor of nearly 6 by cross- (open full item for complete abstract)

Committee: Gary Wnek (Committee Chair); Lei Zhu (Committee Member); Ica Manas (Committee Member); John Lewandowski (Committee Member) Subjects: Materials Science; Mechanical Engineering; Mechanics; Plastics

Master of Science, The Ohio State University, 2023, Aerospace Engineering

The ingestion of birds or unmanned aerial vehicles (UAVs) into a jet engine is a significant hazard to the safety of aircraft. While bird ingestions have been extensively researched, the threat posed by UAVs is a more recent concern due to their rise in popularity. To gain a better understanding of the dangers of UAV ingestions, it is useful to compare to ingestions of birds of similar size. This analysis is an important initial step in determining how previous knowledge regarding soft body impacts (i.e., bird impacts) relates to hard body impacts (i.e., UAVs). To properly analyze these ingestions, the use of a representative fan model that would be certified to be airworthy is used. This model includes a fan with representative boundary conditions for ingestion, including blade retention systems, nose cone, casing, and shaft. Additionally, the bird models and UAV models should be experimentally validated to have credible results. Ingestion simulations with these models will provide a better understanding of how different sizes of soft and hard bodies affect the fan during take-off, better-preparing manufacturers and operators alike for the unfortunate event.

Committee: Randall Mathison (Committee Member); Dr. Kiran D'Souza (Advisor) Subjects: Aerospace Engineering; Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2023, Materials Science and Engineering

Background: A land-based Industrial gas turbine (9HA) lies at the heart of two world records for efficient power generation. Based on thermodynamic principles, the efficiency of gas turbines is dictated by their operating temperatures. Thus, the drive for more efficient power generation ultimately revolves around increasing the operating temperature of gas turbine engines. Specifically, developing a more efficient powerplant requires a gas turbine wheel operating at or above 1200°F (649°C). However, because of the massive size of such turbine wheels (average reported diameters are about 40''), no current superalloy can meet the above temperature goals. In fact, because of its large size, maintaining microstructural stability during the thermomechanical processing of gas turbine wheels is a herculean task. The Unknown: However, most polycrystalline superalloys, including the current state-of-the-art wheel material (Alloy 706), exhibit a hierarchy of microstructures spanning multiple length scales. In that case, microstructural optimization reliant on intragranular precipitate phases alone may not achieve the desired high-temperature performance. Objectives and Findings: The present research focused on optimizing the microstructure of polycrystalline superalloys through concurrent multi-scale structure-property correlation studies. Specifically, I looked at three aspects of the hierarchical nature of the microstructure observed in any typical polycrystalline superalloy: (1) intragranular precipitate distribution, (2) precipitation and consequent precipitate-free zones near annealing twin boundaries, and (3) secondary precipitate evolution on high angle grain boundaries. Our results indicate that unless alloy development strategies utilize a simultaneous optimization approach for these three aspects, achieving the desired high performance in Ni-Fe-based superalloys is difficult. Results from several advanced characterization experiments using various in-si (open full item for complete abstract)

Committee: Michael J. Mills (Advisor) Subjects: Materials Science

Doctor of Philosophy, University of Akron, 2023, Polymer Science

Polymeric materials possess many useful properties, especially low density and high toughness. When crystallized, solvent resistance and temperature resistance are imparted. Predrawing can enhance their mechanical strength and toughness. However, whereas semicrystalline polymers (SCPs) like polyethylene (PE) and polypropylene (PP) are ductile, poly(lactic acid) (PLA) and poly (hydroxyalkanoates) (PHA) often show brittle behavior. In the face of a worldwide push for sustainable materials, it has become necessary to uncover the molecular picture that governs the processing-structure-property (P-S-P) relationships regarding the ductility (or lack thereof) of polymers. One example is how various types of predeformation can affect the mechanical properties. It has been shown [1] that pre-melt stretching of PLA in the near-affine limit close to the glass transition temperature Tg was shown to greatly enhance the strength and ductility of otherwise brittle PLA, and to produce a nanoconfined (NC) crystalline state whose length scale is on the order of the mesh size of the deformed chain network. Furthermore, this melt stretched PLA contained significant crystallinity and was transparent. In Chapter I, we show that after pre-melt shearing of amorphous PLA above Tg, the resultant crystalline and transparent PLA remains brittle. Both atomic force microscopy imaging (AFM) and small-angle x-ray scattering (SAXS) verify that melt-shearing has also produced an NC crystalline state. However, the brittle behavior of the melt-sheared PLA demonstrates the importance of having geometric condensation from processing. A similar NC crystalline state was generated in melt-sheared PET, thereby demonstrating the apparent universality of the methodology. In Chapter II, the P-S-P relationships are explored for SCPs that are crystallized under quiescent conditions. Since a disproportionate extent of effort has gone into researching the mechanisms of yielding rather than the origins of brittl (open full item for complete abstract)

Committee: Shi-Qing Wang (Advisor); James Eagan (Committee Chair); Fardin Khabaz (Committee Member); Mesfin Tsige (Committee Member); Toshikazu Miyoshi (Committee Member) Subjects: Physics; Plastics