Doctor of Philosophy, University of Akron, 2007, Polymer Science

Significant interest in nanotechnology is stimulated by the fact that materials exhibit qualitative changes of properties when their dimensions approach nanometer scales. Quantization of electronic, optical, and acoustic energies with nanoscale dimensions provides exciting, novel functions and opportunities, with interests spanning from electronics and photonics to biology. Characterizing the behavior of nanoscale materials is critical for the full utilization of such novel properties, but metrology for nanostructures is not yet well developed. In particular, mechanical properties of nanoscale particles or features are critical to the manipulation and stability of individual elements, yet changes in mechanical and thermodynamic properties in nanostructured materials create complications in fabrication. This thesis involves the application of Brillouin light scattering to quantify and utilize confinement induced vibrational spectra to understand phononics and elastic properties of nanostructured materials. Measurement and proper interpretation of acoustic waves in polymeric, inorganic, and biological nanostructures provides information about elastic properties and self-assembly. Brillouin light scattering was used to study the vibrational spectra of two-dimensionally confined photoresist and silicon oxide nanolines and three-dimensionally confined poly(methyl methacrylate) spheres and spherical-like viruses. These applications extend the capabilities of Brillouin from characterization of thin films and well-defined spheres to more complex structures. Acoustic waves propagating along the polymeric and silicon oxide lines allowed determination of modulus and its anisotropy. An unexpected acoustic mode was identified in the spectra from nanolines that provided a means to measure mechanical anisotropy. In polymeric lines as narrow as 88nm, neither a change in elastic properties relative to bulk elastic values nor anisotropy in elastic constants was observed. The acoustic (open full item for complete abstract)

Committee: Alexei Sokolov (Advisor) Subjects:

Doctor of Philosophy (Ph.D.), University of Dayton, 2024, Electrical and Computer Engineering

Additive manufacturing (AM) technology is rapidly advancing across diverse fields. For instance, the use of robotic arms in various AM processes has led to significant gains in printing flexibility and manufacturing scalability. However, despite these advancements, there remains a notable research gap concerning the mechanical properties of parts 3D-printed with robotic arms. This study focuses on developing a robotic fused filament fabrication (FFF) 3D-printing process with a layer resolution of 50 μm to 300 μm. The impact of the robotic printing process on the mechanical properties of printed parts is investigated and benchmarked against a commercial FFF 3D printer. In addition, we propose a novel tool path that can vary contour layer thickness within an infill layer to improve mechanical strength by minimizing air gaps between contours. SEM images suggest that this new tool path strategy leads to a significant reduction in the fraction of the void area within the contours, confirmed by a nearly 6% increase in the ultimate tensile strength. Furthermore, a novel strategy for non-planar contours is proposed, specifically designed for thin-shell 3D models. This approach aligns tool paths parallel to the Z-axis, organized into triangular segments, and utilizes planar slicing techniques. The method involves segmenting the point cloud and systematically printing non-planar contours on top of the planar contours. Axial compression testing reveals that samples produced using this strategy exhibit mechanical properties comparable to those of conventional 3D printing. However, distinct fracture patterns are observed: in conventional 3D-printed samples, fractures occur on both inner and outer surfaces, while in non-planar printed samples, fractures are confined to the inner surfaces (planar contours) and do not propagate to the outer non-planar contours. This demonstrates the potential of non-planar printing for improved structural integrity.

Committee: Raul Ordonez Dr. (Advisor) Subjects: Electrical Engineering; Mechanical Engineering; Plastics; Robotics

Master of Science in Engineering, Youngstown State University, 2024, Department of Mechanical, Industrial and Manufacturing Engineering

Hybrid Additive Manufacturing (Hybrid AM) is a method of additively building and machining a three-dimensional part through layering of material and periodically machining to net-shape or finished shape. This research is designed to explore the relationship of the printing parameters of Invar 36 and its mechanical behavior through mechanical testing, microstructure and chemical composition characterization. The additive builds were made using the same process parameters and built in two orientations (XY and Z) and three directions (0°, 45°, and 90°). The printing directions had the largest effect on the mechanical properties when the directions caused a longer print time or a greater thermal load on the parts. The parts built in the XY BRP45 orientation and direction show an average ultimate tensile strength of 384.3 MPa and Rockwell Hardness B averages of 39.4. Based on the chemical analysis and the light and electron microscopy investigations several factors affecting the mechanical behavior of as-printed parts are grain size, manufacturing defects (voids and cracks), inclusions, and chemical segregations. Following the Hall-Petch equation there is a direct correlation between the material yield strength and grain size. In the printed parts the grain size and orientation are controlled by different cooling conditions. Conduction cooling at the interface between print and build plate creates the condition of textured structure. In this case the elongated grains are formed, with the longitudinal axes perpendicular to the build plate (XY bottom samples). In the case of Z oriented samples variation in convection cooling conditions creates different microstructure between the front and back samples. Ti-inclusions seems to be due to the printing environment, since no Ti is listed in the nominal chemical composition of the Invar 36 starting wire.

Committee: Constantin Solomon PhD (Advisor); Brian Vuksanovich PhD (Committee Member); Pedro Cortes PhD (Committee Member) Subjects: Engineering; Mechanical Engineering

Doctor of Philosophy, University of Akron, 2024, Polymer Science

Polyethylene (PE) and isotactic polypropylene (iPP) are the two most abundant commodity plastics. However, these materials are incompatible in the melt blend due to the different surface energies owing to the difference in their microstructures. The transfer of stress between incompatible phases of these polymers is a challenge that contributes to mechanical recycling process losses. This prevents the mixed mechanical recycling of these polymers to yield commodity plastics for high performance applications compared to the virgin resins. As a result, there is a lack of incentive to recycle mixed plastic waste, thereby contributing to plastic pollution in the environment. Compatibilizer additives improve the performance of these blends, through non-covalent, supramolecular, and covalent interactions across PE/PP interfaces. By introducing a small amount of compatibilizer into recycled polyolefin blends, there is potential to enhance the properties, reduce waste plastic, and achieve these in economical fashions. This work investigates several methods of delivering copolymer reinforcing agents which include supramolecular coupling through diverse architectures, namely diblock structures that are proposed to form in-situ and preformed multiblock architecture. The first part of this work will highlight the synthesis of a compatibilizer system consisting of end-functionalized iPP and HDPE. These materials are referred to as Interfacial Supramolecular Coupling Agents (ISCAs) due to their proposed ability to form supramolecular H-bonds across the bulk PE/PP interfaces. The synthesis of high melting-temperature iPP with controlled molecular weight and end-group fidelity is described. Through a sequence of reactions, vinyl end-functionalized iPPs and PEs are converted to β-alanine trimer terminated polyolefins, which are being studied as potential compatibilizers for PE/PP blends. A second strategy describes the use of pre-synthesized multiblock compatibilizers which have hi (open full item for complete abstract)

Committee: Toshikazu Miyoshi Dr. (Committee Member); James Eagan Dr. (Advisor); Donald Quinn Dr. (Committee Member); Junpeng Wang Dr. (Committee Member); Mesfin Tsige Dr. (Committee Chair) Subjects: Chemical Engineering; Chemistry; Materials Science; Plastics

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

Li-ion batteries (LIB) have been spotlighted as a promising power source to replace traditional fuel gases owing to their high energy density, lightweight, and greenhouse gas emission free characteristics. Nevertheless, the catastrophic failure of the LIB is usually connected to safety issues, and the solutions must be addressed from the perspective of materials and designs. The representative materials for the current collectors in LIB are the commercial pure-grade aluminum (Al) and copper (Cu) foils because of their high electrical conductivities, electrochemical stabilities, and low density. However, they degrade during the multiple charge/discharge cycles when the applied voltage exceeds their corrosion potentials. The current flows generate the resistance heating during the charge/discharge cycles at the joint between the foil stacks and the lead tab, increasing the cell temperature. This accelerates the degradation of the foil and reduces the life cycle of the LIB. To reduce the electrical resistance, the increase in conductive area is desirable. Therefore, securing the large joint area with minimal weld discontinuities not only improves the mechanical properties helps but also impedes the resistance heating in LIB. The conventional resistance spot welding (RSW) process has not been widely used to produce the joint between the current collectors and the lead tab so far because of the high thermal, electrical conductivity and thinness of the Al and Cu weld stacks. These aspects generally lead to the smaller weld nugget size, and the sticking of the weld stacks to the electrodes. A recently developed hybrid joining process, known as ultrasonic-assisted resistance spot welding (URW), shows the great effects on increasing the weld nugget size as well as mechanical properties in various pairs of similar and dissimilar metal sheets by the microstructure modification. In the present study, multiple thin pure aluminum (Al) and copper (Cu) foils and tab stacks are (open full item for complete abstract)

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

Master of Science in Engineering, Youngstown State University, 2024, Department of Civil/Environmental and Chemical Engineering

Direct energy deposition (DED) is an additive manufacturing technique which is gaining traction for manufacturing metal components. This study investigated the influence of build orientation and process parameters on the mechanical properties and microstructure of SS316L components fabricated using Laser Hot Wire deposition (LHWD) technique. Experimental methodologies include tensile testing, hardness analysis, microstructural characterization, and bead analysis that provides valuable insights into the effects of process parameters and build orientation on material properties. The results revealed a noticeable variation in tensile strength and hardness across various build orientations, with Unidirectional 0° (U0) demonstrating superior tensile strength which was followed by Unidirectional 90° (U90) and Bidirectional 0° (B0). Microstructural analysis further gives the information on the impact of thermal gradients on grain structure and phase distribution, highlighting the role of build orientation in determining mechanical performance. Additionally, bead analysis and microscopy provide detailed observations of melt pool formation and interlayer bonding thus contributing to a deeper understanding of the LHWD fabrication process. XRF and elemental analysis confirmed that the fabrication process successfully preserved the elemental composition of the SS316L wire feedstock. XRD analysis explained the expected face-centered cubic (FCC) austenitic structure in both the as-received wire and the fabricated components. However, a minor shift in peak positions and lower intensity for some peaks were observed in the fabricated parts. These variations could be due to residual stress or minor microstructural changes introduced during the printing process.

Committee: Bharat Yelamanchi PhD (Advisor); Pedro Cortes PhD (Committee Member); Holly Martin PhD (Committee Member) Subjects: Chemical Engineering; Mechanical Engineering; Meteorology

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, Miami University, 2023, Mechanical and Manufacturing Engineering

Owing to their superior properties like excellent mechanical strength, thermal and oxidation resistance, chemical stability, biocompatibility, chemical resistance, etc. zirconia-based ceramics find their applications in industries, including aerospace, automotive, biomedical, energy, etc. But manufacturing parts of zirconia-based ceramic by traditional manufacturing processes like injection molding, hot pressing, cold pressing, etc., provides difficulties in fabricating high-quality parts with complex geometrical shapes. Additive manufacturing (AM) can be a solution to this problem. Various AM techniques, including binder jetting, selective laser sintering, material extrusion, etc., have been utilized to manufacture complex shapes using zirconia-based ceramic. It remains a challenge to fabricate good-quality parts using AM techniques. From the published report, it is also evident that zirconia-based ceramics show inferior mechanical properties. In this research, inkjet-based AM, which is a material extrusion-based AM technique, is used to fabricate high-quality zirconia-based ceramic. Moreover, zirconia-based ceramic is reinforced with graphene to improve mechanical, thermal, and microstructural properties, and the effects of graphene on these properties as well as on cell adhesion have been analyzed.

Committee: Dr. Yingbin Hu (Advisor); Dr. Muhammad P. Jahan (Committee Member); Dr. Jinjuan She (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy (Ph.D.), Bowling Green State University, 2023, Photochemical Sciences

To correlate and be able to tune the photophysical properties of molecular scale chromophores with the mechanical properties of the macroscale supramolecular polymer such as viscosity, modulus etc. is a complex phenomenon. To tune these properties, we utilize dynamical coordination bonds such as Metal-Ligand interactions. In this work, we present how we can use the photophysical properties specifically probing excited state arising from these tunable dynamical interactions to probe the mechanical properties of the macroenvironment real time in-situ. Utilizing this approach, we were able to detect the viscosity of supramolecular polymeric assembly by probing emission lifetime from triplet electronic state of [Cu(diptmp)2]2+. However, this correlation is not quantitatively ubiquitous in every polymeric host. We probed the reversibility of the polymeric assembly by swelling and deswelling the polymer assembly which is attributed to micro-viscosity. The photophysical changes were of significant magnitude to be able to detect even small reversible changes during swelling and deswelling the polymer. Furthermore, worked on synthesizing a bio-based polymer and made a composite material with multiple ligand moieties. We present how these moieties interact with the polymeric environment and quantify them through their affinity to different metals. The photophysical changes in emission of a bio-based Cu-curcumin polymeric composite material upon applying stress to the composite material has been discussed. We also present to show whether we can induce the photophysical changes in NIR emission of a water soluble [Cr(ddpd)3]3+ complex termed as molecular ruby exhibiting upon subjecting it to thin supramolecular films with increasing modulus and looked at its stress-response.

Committee: Alexis D. Ostrowski Ph.D. (Committee Chair); Francisco Cabanillas Ph.D. (Other); Joseph C. Furgal Ph.D. (Committee Member); Alexander N. Tarnovsky Ph.D. (Committee Member) Subjects: Chemistry; Inorganic Chemistry; Physical Chemistry

Master of Science (MS), Ohio University, 2023, Mechanical Engineering (Engineering and Technology)

Bituminous coal was utilized as a particulate filler in polymer-based composites to fabricate standard 1.75 mm coal-plastic composite filaments for use in commercially available fused deposition modeling 3D printers. The composites were formulated by incorporating Pittsburgh No. 8 coal into polylactic acid, polyethylene terephthalate glycol, high-density polyethylene, and polyamide-12 resins with loadings ranging from 20 wt.% to 70 wt.%. CPC filaments were extruded and printed using the same processing parameters as the respective neat plastics. All coal-plastic composite filaments exhibited uniform particle dispersion throughout the microstructure. The mechanical properties of the 3D printed composites were characterized and compared to composites fabricated using traditional compression molding. Tensile and flexural moduli as well as hardness had direct proportionality with increasing coal content while flexural strength, tensile strength, and impact resistance decreased for most composite formulations. Interestingly, polyamide-based composites demonstrated greater maximum tensile and flexural strengths than unfilled plastic. Microscopy of as-fractured samples revealed that particle pull-out and particle fracture were the predominant modes of composite failure. The introduction of coal reduced the coefficient of thermal expansion of the composites, ameliorating the warping problem of 3D printed high-density polyethylene and allowing for additive manufacturing of an inexpensive and widely available thermoplastic. The high-density polyethylene composites demonstrated increased heat deflection temperatures, but all composites maintained comparable glass and metal transition temperatures, allowing them to be processed with commercial 3D printer extruders. The composites exhibited decreased specific heat capacities suggesting lower energy requirements for processing the material. Coal reduced the composite thermal conductivities compared to the neat plastics but improv (open full item for complete abstract)

Committee: Jason Trembly (Advisor); Yahya Al-Majali (Committee Member); Brian Wisner (Committee Member); David Drabold (Committee Member) Subjects: Engineering; Materials Science; Mechanical Engineering; Sustainability

Doctor of Philosophy (PhD), Ohio University, 2023, Chemical Engineering (Engineering and Technology)

Awareness of microbiologically influenced corrosion (MIC), which threatens assets in the marine, oil and gas, water utilities, power generation, and various other industries, is growing. At least 20% of all corrosion losses can be attributed to MIC. MIC can also cause mechanical property degradation, resulting in metal fracturing, rupturing, collapsing, and cracking that reduce equipment service life and threaten safety. Sulfate reducing bacteria (SRB) such as Desulfovibrio vulgaris and Desulfovibrio ferrophilus (strain IS5) are a major type of microbe that cause MIC. The latter is several times more corrosive. SRB are anaerobic bacteria that can use sulfate as the terminal electron acceptor in their respiration. Unlike soluble organic carbon, elemental iron releases electrons extracellularly, and then the electrons are used in sulfate reduction inside the SRB cytoplasm under bio-catalysis, which requires extracellular electron transfer (EET). Thus, this type of MIC is labeled as “EET-MIC”, which is the result of the demand for energy by sessile cells in biofilms that can perform EET. In practical applications, mechanical property degradation and stress corrosion cracking (SCC) caused by MIC can result in disastrous consequences such as pipeline ruptures and support beam collapses. In the past, most studies on MIC only investigated the MIC mechanisms that lead to pinhole leaks. The effects of microbes and MIC on mechanical property degradation and SCC are also important, if not more. In this work X80 carbon steel was used as an example of pipeline steel. The following topics and results are reported in this dissertation: (1) The relationship between tensile stress and D. vulgaris MIC was explored to study biotic SCC. In the presence of an applied tensile stress most pronounced in the outer bottom of an X80 U-bend, D. vulgaris MIC initiated crack formation in the ATCC 1249 culture medium at 37oC in an anaerobic bottle. The biotic corrosion weight loss of the X8 (open full item for complete abstract)

Committee: Tingyue Gu (Advisor); Sumit Sharma (Committee Member); Peter Coschigano (Committee Member); Marc Singer (Committee Member); Xiaozhuo Chen (Committee Member) Subjects: Chemical Engineering

Doctor of Philosophy (Ph.D.), Bowling Green State University, 2022, Photochemical Sciences

Nature provides a wide range of biopolymers that have been used over the years to create different materials with different properties. Among these biopolymers, we used polysaccharides to develop sustainable materials with unique properties. To enhance their properties, we tried recreating the hierarchal assemblies found in nature between soft organic and hard inorganic components. In other words, our approach was to use metal coordination to ligand groups present in the polysaccharides to make materials with unique mechanical properties and water stability. We also wanted to be able to use light to modify the properties of these materials or degrade them. We chose to work with Fe(III) and V(V) metal ions because these two metals ions showed photoreactivity with different ligands such as carboxylate-containing polyuronates such as alginate and pectin, and other polysaccharides such as chitosan and cellulose and small hydroxy acids such as tartaric acid. First, we studied the photoreactivity of V(V) with two polysaccharides, alginate and chitosan in aqueous solution. In both solutions, a decrease in viscosity was observed with light irradiation accompanied by a change in color from an initial yellow color to a blue color corresponding to the photochemical reduction of V(V) to V(IV) according to previous studies. Second, we made solid films from pectin and chitosan and improved their properties using V(V) ion coordination. V(V)-coordinated films showed increased strength and water stability compared to V(V)-free films. The photochemical reaction observed in solution was also observed in solid state. Finally, to further understand the photochemical reaction in solid state, we made films by blending two of the three polysaccharides, either pectin and chitosan or pectin and ᴋ-carrageenan with different Fe-species. We learned that rheological properties and photochemical properties can be tuned by changing the blend of polysaccharide (open full item for complete abstract)

Committee: Alexis D. Ostrowski Ph.D. (Committee Chair); Xiangdong Xie Ph.D. (Other); Alexander Tarnovsky Ph.D. (Committee Member); Joseph C. Furgal Ph.D. (Committee Member) Subjects: Chemistry; Polymer Chemistry; Polymers

Master of Science in Mechanical Engineering, University of Toledo, 2022, Engineering

The mechanical properties of metal additively manufactured parts are often inferior to those of their traditionally manufactured counterparts. These inferior mechanical properties are mostly attributed to prevalent defects inherent to additive manufacturing processes, thus resulting in reduced performance and durability of the additively manufactured parts. Additive manufacturing processing parameters and post-processing techniques have been studied to determine the optimal conditions for improving the mechanical properties of additively manufactured parts. In this work, the effects of four heat treatment schedules and three build directions were studied on the material microhardness, surface roughness, and surface porosity of selective laser melted 15-5 precipitation hardened stainless steel dog bone test samples. Vickers microhardness test was conducted to obtain hardness values for each test sample. Contact and non-contact type methods were used to determine the surface roughness of every test sample. Microscopic imaging was used to detect and quantify the surface porosity of each test sample. The experimental data was analyzed using an ANOVA test. The heat treatments affected the material hardness of the test samples, raising the Vickers hardness value for all test samples subjected to any heat treatment. The build direction affected the surface porosity of the test samples. Test samples manufactured in the X-build direction experience a greater surface porosity than test samples built in other orientations. The surface roughness was unaffected by either heat treatment or build orientation.

Committee: Ala Qattawi (Committee Chair); Meysam Haghshenas (Committee Member); Adam Schroeder (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy, University of Toledo, 2022, Engineering

Superelastic (SE) Nitinol (NiTi) could be a great candidate for a wide range of applications in the biomedical and aerospace industries. Despite its unique properties, fabrication still remains a challenge and is of high interest. To address the limitations, laser-based powder bed fusion (LPBF) additive manufacturing (AM) has been developed and used for the fabrication of superelastic NiTi components. However, in most SE applications NiTi components undergo cyclic loadings. There is, however, limited work on the fatigue life of NiTi components fabricated with LBPF. In general, different parameters starting from the powder preparation to process parameters, build conditions, and post-processing directly affect the microstructural and mechanical properties of the LBPF fabricated NiTi parts. After providing an introduction chapter, this work is organized into three papers, each forming one chapter of the dissertation, and there is a summary and conclusion as a final chapter. In the second chapter, the effect of build orientation on the fatigue behavior of the LBPF fabricated NiTi parts was evaluated. NiTi dog-bone samples with three different build orientations were fabricated and used to investigate the monotonic tensile and fatigue behavior of the material. In addition to the mechanical experiments, fracture surfaces of the monotonic and fatigue samples were evaluated, and different types of defects were assessed. It was shown that the samples fabricated on their edge has a low level of scattering in comparison to the other sample fabricated horizontally or in 45-degree. Since internal defects and unwanted porosities were recognized as a major cause of the fatigue failure, the remelting process was proposed as a potential solution to improve the parts' relative density and reduce internal pores. In the third chapter, to achieve a set of optimized process parameters for the remelting process, selective laser remelting with different process parameters was designe (open full item for complete abstract)

Committee: Mohammad Elahinia (Committee Chair); Mohammad J. Mahtabi (Committee Co-Chair); Mohamed Samir Hefzy (Committee Member); Ala Qattawi (Committee Member); Meysam Haghshenas (Committee Co-Chair) Subjects: Materials Science; Mechanical Engineering; Mechanics

Doctor of Philosophy, University of Toledo, 2022, Physics

In this dissertation the structural properties of bulk alloys and thin-films are studied using a variety of di erent techniques including density functional theory (DFT) and accelerated dynamics. The first part of this dissertation involves the use of DFT calculations. In particular, in Chapter 3 the stability and mechanical properties of 3d transitional metal carbides in zincblende, rocksalt, and cesium chloride crystal structures are studied. We find that the valence electron concentration and bonding configuration control the stability of these compounds. The filled bonding states of transition metal carbides enable the stability of the compounds. In the second part of this dissertation we use a variety of accelerated dynamics techniques to understand the properties of growing and/or sublimating thin-films. In Chapter 4, the results of temperature-accelerated dynamics (TAD) simulations of the submonolayer growth of Cu on a biaxially strained Cu(100) substrate are presented. These simulations were carried out to understand the e ects of compressive strain on the structure and morphology. For the case of 4% compressive strain, stacking fault formation was observed in good agreement with experiments on Cu/Ni(100) growth. The detailed kinetic and thermodynamic mechanisms for this transition are also explained. In contrast, for smaller (2%) compressive strain, the competition between island growth and multi-atom relaxation events was found to lead to an island morphology with a mixture of open and closed steps. In Chapter 5, we then study the general dependence of the diffusion mechanisms and activation barriers for monomer and dimer diffusion as a function of strain. The results of TAD simulations of Cu/Cu(100) growth with 8% tensile strain are also presented. In this case, a new kinetic mechanism for the formation of anisotropic islands in the presence of isotropic diffusion was found and explained via the preference for monomer diffusion via exchange over hopp (open full item for complete abstract)

Committee: Jacques Amar Professor (Advisor) Subjects: Physics

Doctor of Philosophy, The Ohio State University, 2022, Industrial and Systems Engineering

In the present study, a multiscale modeling approach is developed to investigate the metallurgical and mechanical characteristics of tubular material undergoing tube hydroforming and subsequent annealing processes. This study is performed in three steps. First, a modeling setup based on the Cellular Automata (CA) model is developed to predict the kinetic of static recrystallization (SRX) in hydroformed steel tubes undergoing the isothermal annealing process. To assess the accuracy of the CA model, experimental and predicted results are compared in terms of grain topology data including the grain size and aspect ratio distributions, as well as the rate of softening during annealing. Second, a hierarchically coupled CA model, crystal plasticity finite element method (CPFEM), and thermal finite element (FE) model is developed to predict the softening kinetics of the bulged steel tube during non-isothermal annealing. Through the developed model, the kinetics of softening mechanisms including static recovery (SRV) and SRX, as well as the recrystallization texture are predicted. The corresponding experimental data are utilized to calibrate and verify the implemented CPFEM model for simulation of tube hydroforming process, thermal FE model for prediction of the local temperature over annealing time, and CA algorithm for modeling of the softening kinetics and texture evolution throughout the annealing process. Third, a multiscale modeling approach based on CPFEM algorithm is proposed to predict the mechanical properties in the deformed and annealed specimens. To that end, CPFEM modeling of the deformation behavior in metals consisting of second phase particles is performed based on Representative Volume Element (RVE) models. The RVE model is generated based on the CA predictions for different anneal specimens. The calibrated CPFEM model is used for the simulation of deformation behavior at macro scale based on RVE models. To validate the developed multiscale approach, the t (open full item for complete abstract)

Committee: Farhang Pourboghrat (Advisor); Michael Groeber (Committee Member); Alan Luo (Committee Member) Subjects: Engineering; Materials Science; Mechanical Engineering

Doctor of Philosophy, University of Akron, 2022, Mechanical Engineering

Material extrusion processes have been increasingly employed in the fabrication of advanced ceramics in the aerospace, automotive, and biomedical fields. Such processes—which involve printing compositions containing ceramic powders and sacrificial binders, debinding the binders, and sintering the parts to obtain pure ceramics—can be used to produce more complex structures than traditional ceramic manufacturing techniques. In this study, a rod-shaped feedstock comprised of binder-coated zirconia containing 87 wt% zirconia was supplied to a motorized piston extruder in a customized 3D printer to fabricate green ceramic structures, and the structures were then subjected to debinding and sintering. A comprehensive set of characteristics were examined: the thermal and rheological properties of the feedstock, the printability of the feedstock, the influence of the layer thickness and raster angle on the surface roughness and flexural/tensile/compressive strengths of the sintered zirconia, Vickers hardness, relative density and porosity, shrinkage behavior, and the micro/macro structure of green and sintered 3D-printed zirconia structures. The comprehensive characteristics of 3D printed green and sintered zirconia that were obtained in this study can facilitate the successful 3D printing of ceramics. Next, for extending the functionality and applications of parts produced by additive manufacturing, an inductive proximity sensor with a 3D-printed ceramic housing and embedded sensing elements was designed and produced using a hybrid manufacturing process in which the printing process is paused, and a sensing element is embedded into the printed structure. In the developed process, binder-coated zirconia was used to fabricate the ceramic housing for the sensor, and platinum wire was used in the sensing element. The subsequent debinding and sintering processes achieved a nearly fully dense ceramic housing that protects the sensor in harsh environments. Furthermore, zirconia fe (open full item for complete abstract)

Committee: Jae-Won Choi (Advisor); Gregory N Morscher (Committee Member); Jiang Zhe (Committee Member); Kwek-Tze Tan (Committee Member); Kye-Shin Lee (Committee Member); Sadhan C Jana (Committee Member) Subjects: Mechanical Engineering

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

Composites filled with natural fillers have been used in high-volume applications including automotive and construction industries due to their performance, economic, and environmental advantages. Herein, the development of new more-sustainable coal plastic composite (CPC) materials, engineered as a better substitute for the state-of-the-art wood-plastic composites (WPC) is presented. Bituminous Pittsburgh No.8 (P8) and sub-bituminous Powder River Basin (PRB) coals with varying coal content (40-70 wt.%) were individually melt-mixed with high-density polyethylene (HDPE). Mechanical, thermal, and flammability properties of CPC materials were characterized and compared with predominant commercially available WPC products. Composites' microstructure examination revealed better adhesion between coal and HDPE with less porosity than WPC. Differential scanning calorimetry analyses indicated potential chemical reactions between the coal and HDPE, which was not evident in the WPC. Despite the inverse proportionality of tensile strength with the coal content, CPC with 60 wt.% P8 was not significantly different from a typical WPC formulation. CPC flexural strength increased to a maximum value, after which it decreased. Tensile and flexural moduli have direct proportionally with the coal content increase. CPC with 60 wt.% P8 coal possessed higher flexural strength and, in some cases, comparable flexural modulus in comparison to WPC products. FEA models indicated a hollow profile would potentially have a better load-deflection curve with less localized stresses as compared to several types of profiled sections with the same weight reduction. Thermo-oxidative analyses indicated substantially higher oxidation induction time and higher overall activation energy for CPC with 60 wt.% in comparison to neat HDPE and most WPC products, suggesting higher thermo-oxidative stability and better end-use service life. Thermo-oxidative analyses suggest (open full item for complete abstract)

Committee: Jason Trembly (Advisor) Subjects: Chemical Engineering; Mechanical Engineering

Master of Sciences (Engineering), Case Western Reserve University, 2022, Biomedical Engineering

This study investigated the effects of Ar/H2O plasma treatment on the surface and bulk properties of polytetrafluoroethylene (PTFE) and polyethylene terephthalate (PET) surgical mesh materials as a method to modify and mitigate biofouling events that reduce their performance. With regards to bulk properties, findings from uniaxial tensile testing of these substrates in mesh and suture form show that plasma treatment can weaken their tensile properties. Increasing treatment duration and surface area to volume ratio were found to be major factors that resulted in further reduction of these properties. With regards to surface properties, the direct application of plasma on these substrates was not found to reduce biofouling in the form of protein adsorption and S. aureus attachment compared to untreated control surfaces. These experiments suggest that the deposition of a subsequent coating after plasma treatment is needed to further control biofouling events and is a future direction worth investigating.

Committee: Horst von Recum PhD (Advisor); Julie Renner PhD (Committee Member); Sam Senyo PhD (Committee Member) Subjects: Biomedical Engineering

Master of Sciences (Engineering), Case Western Reserve University, 2022, Materials Science and Engineering

The effects of changes in process parameters, heat treatment, build orientation, and resulting defects on fatigue behavior of selective laser melting-processed AlSi10Mg have been determined. Samples were prepared under distinct P-V parameters and heat treatments for the following classifications: A- nominal with SR+HIP+T6, B- large defects with SR+HIP+T6, G- small to medium defects with SR+HIP+T6, D- many defects with SR+HIP+T6, E- large defects with SR+T6, and F- small to medium defects with SR+T6. Fatigue crack growth (FCG) testing of bend bars and high cycle fatigue (HCF) fatigue testing of cylindrical samples occurred at a stress ratio R = 0.1 and 20 Hz according to appropriate ASTM standards. This is reviewed along with ASTM-standardized tension testing of cylindrical samples. Increased defects typically reduced UTS, ductility, and fracture toughness particularly in the Z orientation. The S-N performances of X/Y orientation were improved or similar to the Z orientation in HCF as a result of having smaller or similar fatigue-initiating defect sizes, that were quantified for all failed S-N samples. HIP-processing generally reduced fatigue-initiating defects sizes and improved most S-N performances. Compared to SLM AlSi10Mg from literature, the nominal (A) build had an increased HCF performance. HCF sample life was estimated by using fracture surface defect measurements and FCG data obtained for those process conditions.

Committee: John Lewandowski (Committee Chair); Sunniva Collins (Committee Member); Clare Rimnac (Committee Member) Subjects: Materials Science