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

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

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 (PhD), Ohio University, 2022, Mechanical and Systems Engineering (Engineering and Technology)

In this study, it was hypothesized that graphene aluminum alloys can be engineered for improved bulk electrical properties by establishing a form of coherency with aluminum valance and graphene π electrons. To this end, the effects of graphene concentration and process parameters were assessed, and thus shown that improvements in the electrical performance of bulk aluminum alloys is possible. Al/graphene composites were manufactured under varying thermo-mechanical process conditions with varying graphene content embedded into three different aluminum alloy systems, namely AA1100 (commercially pure, non-heat treatable), AA3003 (alloyed, non-heat treatable), and AA6101 (alloyed, heat treatable) alloys. Electrical conductivity and temperature coefficient of resistance were determined for the 10 - 12 AWG composite wires manufactured via solid phase processing techniques, hot extrusion and shear assisted processing and extrusion. Microstructural characterizations were performed through optical and scanning electron microscopy to identify the process-structure-property relationships for the composites. Results showed that hot-extruded AA1100 composites with 0.25 wt.% graphene showed the highest improvement of 2.32% in electrical conductivity as well as the TCR lower by 23.4% compared to control samples manufactured under similar conditions. Enhanced conductivity was seen in composites with higher semimetallic graphene while lower TCR was observed in samples with higher semiconductor graphene concentration. Extrusion pressures played a key role in the exfoliation and deformation of agglomerated graphene nanoparticle precursors. Second phase solubility was affected by hot pressing conditions, extrusion temperature and ShAPE parameters, and not the presence of graphene in the composite microstructures. On the other hand, graphene affected precipitation dynamics during aging of hot-extruded AA6101 composites. Finally, composite grain morphology and distribution as well as pre (open full item for complete abstract)

Committee: Frank Kraft (Advisor); Keerti Kappagantula (Advisor); Muhammad Ali (Advisor); Brian Wisner (Committee Member); Jay Wilhelm (Committee Member); Zaki Kuruppalil (Committee Member); Eric Stinaff (Committee Member) Subjects: Materials Science; Mechanical Engineering

Master of Science (M.S.), University of Dayton, 2021, Mechanical Engineering

To numerically simulate and predict the plastic deformation of aerospace metal alloys during extreme impact events (e.g., turbine engine blade-out and rotor-burst events, and foreign object damage), accurate experimental knowledge of the metal's hardening behavior at large strains is requisite. Tensile tests on round cylindrical specimens are frequently used for this purpose, with the metal's large-strain plasticity ultimately captured by an equivalent true stress vs. equivalent true plastic strain curve. It is now well known that if axial strain is measured using an extensometer, the equivalent true stress-strain curve calculated from this measurement is valid only up to the onset of diffuse necking. That is, once the strain field heterogeneously localizes in the specimen gage (onset of necking), extensometers, which average the strain field over the gage section, are unable to capture the local strain at the site of fracture initiation. Thus, a number of approaches have been proposed and employed to correct the post-necking hardening response. One commonly-used technique is an iterative approach commonly referred to as finite-element model updating (FEMU). This approach involves inputting a suite of candidate post-necking equivalent true stress-strain curves into finite-element software. The true stress-strain curve that produces the best agreement between simulation and experiment is ultimately adopted. In this document, a novel variation of this iterative approach is presented, aimed at decreasing computational expense and iterative effort with a better first guess that bounds this fan of prospective true stress-strain curves. In particular, we use local surface true (Hencky) strain data at the fracture location in an approximate analytical formula to generate a first guess curve and upper bound on the candidate true stress-strain fan of curves. To assess its performance and robustness, the proposed approach is verified using experimental data for a menu of ae (open full item for complete abstract)

Committee: Robert Lowe Ph.D. (Advisor); Luke Sheridan Ph.D. (Committee Member); Dennis Buchanan Ph.D. (Committee Member); Jeremy Seidt Ph.D. (Committee Member) Subjects: Aerospace Engineering; Aerospace Materials; Engineering; Mechanical Engineering; Mechanics

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, 2019, Mechanical Engineering

Chi Ma, University of Akron, May 2019. Improving the plasticity of metallic glass through heterogeneity induced by electropulsing-assisted surface severe plastic deformation. Advisor: Yalin Dong. Co-advisor: Chang Ye. Metallic glasses have raised tremendous interests to industrial and academic community due to its superior properties (e.g. ultimate strength, wear resistance, and soft-magnetic property) since their invention. The amorphous structure, on the one hand, gives rise to advanced material properties while, on the other hand, causes poor ductility hindering the wide application of metallic glasses. Aiming at designing ductile metallic glasses, this thesis research investigates surface severe plastic deformation (SSPD), electropulsing, and their combined treatment to achieve the transition from brittle to ductile, and unveil the relationship between microstructure and mechanical deformation behavior through molecular dynamics simulation and fracture theory. Ultrasonic nano-crystal surface modification (UNSM), as a member of the SSPD family, is a recent developed technology possessing high controllability and good surface finish. By applying ultrasonic mechanical peening, UNSM leads to the dilation of local atomic structure and thus induces extra free volume heterogeneously. Extra free volume is generated after UNSM treatment and consequently plasticity, i.e. yielding and more plastic strain, starts to appear. The observation of fracture surface suggests that before fracture occurs, higher density of shear bands exists in the UNSM-treated samples and severe interaction between shear bands impedes propagation of themselves, which contributes to material plasticity. In addition to extra free volume, the secondary crystalline phase induced by UNSM and its effect on increasing plasticity is also explored. In this thesis, for the first time, the composite structure of nanocrystalline phase co-existed with extra free volume is fabricated by electropulsing-ass (open full item for complete abstract)

Committee: Yalin Dong PhD (Committee Chair); Chang Ye PhD (Committee Co-Chair); Guo-Xiang Wang PhD (Committee Member); Rajeev Gupta PhD (Committee Member); Jun Ye PhD (Committee Member); Kwek-Tze Tan PhD (Committee Member) Subjects: Materials Science; Mechanical Engineering; Metallurgy; Molecular Physics; Molecules; Nanotechnology

Doctor of Philosophy, The Ohio State University, 2015, Welding Engineering

Very High Power Ultrasonic Additive Manufacturing (VHP-UAM) was used to fabricate 10 layers and up to 80 layers samples from aluminum alloy 3003-H18 foil (Al3003-H18) of 150 µm thickness with varying vibration amplitude and normal force. This research was aimed at studying the change in hardness, microstructure, and texture in Al3003-H18 foil both in as-processed conditions and in heat-treated (343°C-2hr) condition compared to original foil, and to utilize neutron diffraction method to characterize the bulk texture analysis of the bulk VHP-UAM samples. Results from Vicker microhardness measurement, optical microscopy, scanning electron microscopy, electron backscattered diffraction (EBSD), and neutron diffraction were used to describe the changes in hardness, microstructure, and texture. The difference in microstructure and texture evolution in VHP-UAM samples processed at different process parameters can be related to the energy input during VHP-UAM and the post-processing heat-treatment.

Committee: Avraham Benatar (Advisor); Sudarsanam Suresh Babu (Advisor); John Lippold (Committee Member); Wei Zhang (Committee Member) Subjects: Materials Science; Metallurgy

Master of Science, The Ohio State University, 2012, Materials Science and Engineering

As engineering devices have reduced to sub-micron scale, materials behavior at small length scale has become increasingly important to understand quantitatively. Over the last few decades, advances in experimental devices for investigating submicron size specimens such as focused ion beam (FIB), nanoindentaion, and submicron-scale uni-axial compression test machine enable novel capabilities to explore extrinsic size effects or sample size effects. Specimen-size-effects-induced mechanical behaviors of FCC and BCC single crystalline metals and their deformation mechanisms are described in the first chapter. In addition, a comparison of the two crystals is summarized. The study on HCP materials is excluded in this review because sufficient experimental data and theories are not available at this point. Directionally solidified NiAl-Mo composites consisting of well-aligned [100] Mo fibers embedded in a [100] NiAl matrix were pre-strained from 0% to 16% along the [100] direction. Samples were then extracted parallel to the [100] direction using focused ion beam (FIB) techniques and their cross-sections were examined via TEM. Also, the NiAl matrix was selectively etched away and the free standing Mo fibers were obtained to study dislocation networks. Preliminary TEM results showed that as-grown samples (without pre-straining) do not contain dislocations in the Mo fiber. In the NiAl matrix, on the other hand, <100>-type dislocations are observed. At intermediate pre-strain level, the <100>-type dislocations in the NiAl matrix are gathered at the inter-phase boundary and form slip transfer zones where stress builds up, which causes activation of <111>-type dislocations in the Mo fiber. The <111>-type dislocations in the Mo fiber are inhomogeneously distributed and its plasticity is determined by a slip transfer mechanism. With increased pre-strain, <111>-type dislocations in the Mo fiber interact with each other and form binary and ternary junctions so that the dislocati (open full item for complete abstract)

Committee: Michael Mills PhD (Advisor); Hamish Fraser PhD (Committee Member) Subjects: Materials Science

Doctor of Philosophy, The Ohio State University, 2008, Materials Science and Engineering

Dislocation propagation in and work hardening of γ channels and directional coarsening (rafting) of γ' precipitates are the major microscopic processes taking place during high temperature deformation of single crystal Ni-base superalloys. Understanding of those processes is crucial for developing improved models of creep and fatigue of turbine blades in aircraft engines. Recent investigations of rafting in superalloys demonstrate clearly the importance of elastic modulus difference between the γ and γ' phases and dislocation-level activities in the γ-channels in determining the kinetic pathway of the processes. The elastic modulus difference can lead to the non-uniform distribution of stresses through the interaction with the lattice misfit and external load. While work hardening in the γ channels has a direct effect on differentiation of the stress state in the vertical and horizontal channels and on γ/γ' interface coherency and energy, and hence influences the diffusive flow and morphological changes of the γ/γ' microstructure. In turn, changes in particle shape and coherency of the interface alter the local stress state and thereby the Peach-Koehler force on dislocations. Although existing models treating these processes separately can offer a qualitative explanation about the direction of rafting for typical superalloys, a complete quantitative understanding of rafting phenomena requires these processes to be treated simultaneously in a common framework because of their intimate coupling. The objective of this thesis is to develop an integrated computational approach in simulating simultaneous evolution of both γ/γ' microstructure and dislocations in an elastically anisotropic and inhomogeneous system by using a single, consistent phase field methodology. In particular, the phase field dislocation model is used to simulate the initial dislocation γ channel filling process and calculate stress distribution associated with complex three-dimensional (3D) dislocati (open full item for complete abstract)

Committee: Yunzhi Wang PhD (Committee Chair); Michael Mills PhD (Committee Member); Suliman Dregia PhD (Committee Member); Sudhir Sastry PhD (Committee Member) Subjects: Materials Science

Doctor of Philosophy, The Ohio State University, 2007, Chemistry

Potentiometric internal reference oxygen sensors were created by embedding a metal/metal oxide mixture within an yttria-stabilized zirconia oxygen-conducting ceramic superstructure. A static internal reference oxygen pressure was produced inside the reference chamber of the sensor at the target application temperature. The metal/metal oxide-containing reference chamber was sealed within the stabilized zirconia ceramic superstructure by a high pressure (3-6 MPa) and high temperature (1200-1300 °>C) bonding method that initiated grain boundary sliding between the ceramic components. The bonding method created ceramic joints that were pore-free and indistinguishable from the bulk ceramic. The oxygen sensor presented in this study is capable of long-term operation and is resistant to the strains of thermal cycling. The temperature ceiling of this device was limited to 800 °C by the glass used to seal the sensor package where the lead wire breached the inner-to-outer environment. Were it possible to create a gas-tight joint between an electron carrier and stabilized zirconia, additional sealing agents would not be necessary during sensor construction. In order to enable this enhancement it is necessary to make a gas-tight joint between two dissimilar materials: a ceramic electrolyte and an efficient ceramic electron carrier. A conducting perovskite, LaxSr1-xAlyMn1-yO3, was joined to YTZP at 1250 °C and 1350 °C. X-ray diffraction was used to gain structural information on the perovskite. Room temperature resistivity measurements were performed on joined and unjoined samples to determine the extent to which joining altered electron conduction within the LSAM. Electron microscopy confirmed that intergranular penetration occurred at the joining plane leading to effective bonding between the two dissimilar ceramics. Raman spectral maps of the joined samples demonstrated that joining temperature determines the extent to which interlayers begin to form in the joining plane. X-r (open full item for complete abstract)

Committee: Prabir Dutta (Advisor) Subjects:

Doctor of Philosophy, The Ohio State University, 2007, Materials Science and Engineering

Micron-sized compression specimens, fabricated using a focused ion beam (FIB), indicate a dramatic strengthening effect as sample dimensions are reduced from 20μm to sub-micron diameters in nickel and gold microcrystals. To understand this effect, novel microscopy techniques were utilized to study the mechanical properties and dislocation substructures from microcrystals of pure nickel, Ti-6wt.%Al, Ti-6Al-2Sn-4Zr-2Mo-0.1Si (Ti-6242) and Ti-50.8at.%Ni. The dislocation behavior that governs plasticity is quite different between each of these materials and as such produces different size effects at small sizes. The nickel compression results indicate a dramatic increase in strength as sample dimensions are reduced. Quantitative dislocation density measurements performed on slip-plane TEM foils extracted from nickel microcrystals indicate an increase in stored dislocation density at smaller sizes. However, hardening contributions from forest-hardening and source truncation hardening were insufficient in explaining the high observed flow stresses. This result suggests that other hardening mechanism are operating in the nickel microcrystals. The titanium alloys exhibit a much less dramatic strengthening effect compared to the nickel microcrystals. The titanium microcrystals, at all sample sizes tested (1-60μm), are stronger than bulk compression specimens. Even at the 60μm sizes bulk behavior is not observed, while at only 20 microns nickel microcrystals exhibit bulk properties. Transmission electron microscopy (TEM) investigations indicate several dislocation pile-ups of both screw and edge character at the microcrystal surfaces. These pile-ups appear to be related to ion damage induced by the fabrication of these samples, resulting in a strengthening effect that follows a Hall-Petch relationship. Nickel-Titanium alloys deform through a phase transformation, as well as dislocation motion. The microcrystal compression results indicate no observable size effect related to (open full item for complete abstract)

Committee: Michael Mills (Advisor) Subjects: Engineering, Materials Science

Master of Science (MS), Ohio University, 1986, Mechanical Engineering (Engineering)

The A.L.P.I.D. 1.41 (Analysis of Large Plastic Increment Deformation) version based on rigid-viscoplaticity and finite element method has been modified for the simulation of hammer forging. As a theoretical background for this modification, three methodologies have been suggested and among them, energy balance method based on the force exerted on dies has been adopted. Also preprocessor program called 'HMINP' for the easy preparation of the input file to run A.L.P.I.D.H. has been developed and a command file to run A.L.P.I.D.H. has been developed.

Committee: Jay Gunasekera (Advisor) Subjects: Engineering, Mechanical

Master of Science in Engineering, University of Akron, 2012, Biomedical Engineering

Treatment options for spinal trauma, chronic disease and/or age degeneration vary based on the medical prognosis and severity of symptoms, with surgery being one treatment option. One of the many surgical options for stabilization is pedicle screw based fusion, where screws are placed into the spine and metal rods are fixed to these screws using set screws. The tightening torque is critical for these procedures, as under or over torquing leads to slippage, decreased strength, and ultimately poor fusion results. Numerous products in the market use a torque wrench or break-off set screws that ensure the correct tightening torque. The focus of this thesis is to develop techniques (based on geometrical alterations without changing the material) that modify the set screws so that they reduce shock (200-800 g-force) while still ensuring the correct tightening torque. The hypothesis of this thesis is to show that geometric changes in the set screw tightening structure (i.e. device) can reduce the maximum shock by influencing how the stored energy is released, and yet keep the tightening torque the same. The objective is to increase the time period between yielding and fracture and channel more energy towards plastic deformation. The specific aim is to make geometric changes in the grooved region (designed for break off) to cause the ratio of maximum recoverable strain energy to maximum plastic energy dissipation to decrease. Computer models based on fracture mechanics are used to demonstrate this. Using a model for ductile metal Al 5083-H116, it was shown that wider, more gradual grooves lead to a 36% decrease in this ratio. A decrease in this ratio indicates that the maximum g-force shock will decrease since a greater percent of the energy will be dissipated during material deformation. In addition, there was a 74% increase in rotation before failure. This behavior is believed to be beneficial since broken bonds between molecules in the shear band are given more time to r (open full item for complete abstract)

Committee: Ajay Mahajan Dr. (Advisor); Mary Verstraete Dr. (Committee Member); Wieslaw Binienda Dr. (Committee Member); Atef Saleeb Dr. (Committee Member) Subjects: Anatomy and Physiology; Biomechanics; Biomedical Engineering; Biomedical Research; Biophysics; Materials Science; Mechanical Engineering; Medicine