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

Master of Science (M.S.), University of Dayton, 2023, Mechanical Engineering

Fluoroelastomers can maintain their stretchability and elasticity at high temperatures, making them well-suited for applications that require extreme thermal resistance. Presently, there is significant interest in casting compounded fluoroelastomers to create high-temperature seals with intricate geometric features. It is not well understood, however, how these materials will perform mechanically in service as they undergo repeated heat cycling and are subjected to complex, multi-axial stress states. To address this research opportunity, a suite of commercially available compounded fluoroelastomers were thermally aged (10, 20, 50 cycles at 200 °C for 8 hours) and mechanically tested in uniaxial tension and uniaxial compression. Preliminary room-temperature uniaxial tension results displayed increases in strength and elastic modulus with modest heat cycling (20 cycles), followed by a subsequent decrease in strength at large amounts of heat cycling (50 cycles). Even at 50 cycles, however, the heat-conditioned materials still exhibited greater strength than the unconditioned materials. This mechanical response is likely due to a competition between the chemical mechanisms of polymer cross-linking and chain scission, with strength degradation at large amounts of heat cycling reflective of chain scission dominating cross-linking. From this suite of candidate materials, the compounded commercial fluoroelastomer FKM Viton A-500 RB75A5 was downselected for the desired sealant application and subsequently tested at elevated temperatures (85, 140, 200 °C) in uniaxial tension to better understand its behavior in extreme environments. Lower mechanical strength and reduced elongation were observed in the material's elevated temperature response. This is likely because the higher temperatures result in shorter polymer chains, which corresponds to a higher entropy state and a weaker, lower-elongation material. Additional room-temperature tests were performed on Viton RB75A (open full item for complete abstract)

Committee: Robert Lowe (Committee Chair); Donald Klosterman (Committee Member); Chad Jones (Committee Member); Allyson Cox (Committee Member); Thomas Whitney (Committee Member) Subjects: Materials Science; Mechanical Engineering; Mechanics

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, The Ohio State University, 2023, Mechanical Engineering

Conventional sheet metal forming tooling in the automotive industry is made up of hardened steel and used for mass-production. Prototype tooling made of metal is durable, but it is only used for a small number of parts despite its high cost, contributing heavily to the vehicle development cost. Additive manufacturing (AM) offers a cost-effective and rapid tooling option for prototyping, and low cost, low volume sheet metal forming applications. Due to the high anisotropy in mechanical properties of 3D printed composites, accurate characterization, and finite element modeling of the material becomes paramount for successful design and application of these forming tools. This study investigates the feasibility of using AM polymer composite tooling for the stamping of HSS 590 steel sheets through a two-pronged approach – experimental and numerical analysis. Experimental characterization of 3D printed fiber–reinforced polymer composite material was performed at various strain rates. A homogenized material model with orthotropic elasticity and the Hill 1948 anisotropic yield criterion was then calibrated based on these experimental data. Sheet metal stamping experiments were conducted with AM polymer tooling and their performance was evaluated based on various metrics such as tool deformation and part accuracy. Finite element simulations of the stamping of high strength steel sheets using composite tooling were performed and tool deformation were predicted and compared with experimental measurements. FE simulation results were in good agreement with stamping experiments performed with polymer tooling. It was found that the anisotropy and strain rate sensitivity of 3D printed polymer composites play a significant role in their performance as tooling materials. The effective use of simulations in optimizing process parameters to achieve the desired final part geometry is also demonstrated. Fiber reinforced FDM and BAAM produced polymer composite tooling was found to b (open full item for complete abstract)

Committee: Farhang Pourboghrat (Advisor); Jose Castro (Committee Member); Marcelo Dapino (Committee Member); Noriko Katsube (Committee Member) Subjects: Mechanical Engineering; Mechanics

Master of Science, University of Akron, 2023, Mechanical Engineering

Additive Manufacturing (AM) has become a prevalent manufacturing method for complex components that would otherwise be extremely difficult to manufacture using traditional subtractive manufacturing techniques. Typical additive manufacturing processes such as Electron Beam Manufacturing (EBM) and Laser Powder Bed Fusion (LPBF) create components by melting and fusing gas atomized powder material in a layering method. This layering method causes parts to continuously experience thermal cycling during manufacturing that can affect grain growth, inherent residual stresses, and porosity. This push for additive manufacturing technology has reached into military and aerospace applications for manufacturing and repair of complex components such as blisks and blades created with complicated materials such as Nickel-based superalloys. Traditional and common Nickel-superalloys such as Inconel-718 when gas-atomized when additively manufactured tend to have fracture control problems that arise during the manufacturing process and afterwards. Thus, the company Aubert & Duval created a new Nickel-superalloy composition, ABD-900AM, which eliminates crack formation during additive manufacturing processes as well as optimized fatigue crack performance. This thesis aims to characterize the mechanical properties of ABD-900AM manufactured using the LPBF AM process to verify the effectiveness of the alloy and understand the optimization to the fatigue crack properties of the material through uniaxial tensile, Fatigue Crack Growth (FCG), and High Cycle Fatigue (HCF) testing of the alloy in different build orientations. Microstructural and fracture surface analysis using Scanning Electron Microscopy (SEM), and optical microscopy were completed to correlate characteristics shown in mechanical testing.

Committee: Manigandan Kannan (Advisor); Gregory Morscher (Advisor) Subjects: Materials Science; Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2020, Mechanical Engineering

Ultrasonic additive manufacturing (UAM) is a solid-state manufacturing technology that produces near-net shape metallic parts. UAM has been demonstrated to make robust structures with a variety of material combinations such as Al-Al, Al-Ti, Cu-Cu, and Al-Cu. However, UAM welding of high strength steels has proven challenging. The focus of this work is to develop a fundamental understanding of the structure-property-process relationship of UAM steel welding through experiments and modeling. Process and post-processing methods to improve UAM steel weld quality were investigated. A custom shear test was first developed and optimized to test the mechanical strength of UAM builds. The second study demonstrated the UAM fabrication of stainless steel 410 builds which possess, after post-processing, mechanical properties comparable with bulk 410 material. Fracture surface analyses confirm the weld quality improvement caused by increasing the baseplate temperature and the application of hot isostatic pressing (HIP) post weld. In the third study, a higher weld power is demonstrated by using a cobalt-based sonotrode coating, achieving shear strengths comparable to bulk 4130 material without post treatment. Weld parameters for making UAM 4130 builds were optimized via a design of experiments study. Baseplate temperature of 400 ˚F (204.4 ˚C), amplitude of 31.5 µm, welding speed of 40 in/min (16.93 mm/s), and normal force of 6000 N were identified as optimal within the selected process window. Analysis of variance and main effect plots show that normal force, amplitude, and welding speed are significant for interfacial temperature. Similar analyses show that normal force and amplitude have a statistically significant effect on shear strength. Residual stress in UAM 4130 samples was measured for the first time using neutron diffraction. The maximum tensile residual stress for UAM 4130 is found to be relatively low at 176.5 MPa, which suggests a potentially better fatig (open full item for complete abstract)

Committee: Marcelo Dapino (Advisor); David Hoelzle (Committee Member); Farhang Pourboghrat (Committee Member) Subjects: Materials Science; Mechanical Engineering

MS, University of Cincinnati, 2019, Engineering and Applied Science: Materials Science

In this project the effect of polyacrylonitrile (PAN) on thermal and mechanical properties of polyimide (PI) was studied. The aim of this study is to formulate multifunctional polyimide/polyacrylonitrile film by combining excellent properties of polyimide such as high solvent and wear resistance, high dimensional stability, excellent thermal resistance and high modulus with the superior properties of polyacrylonitrile such as low density, thermal stability, high strength and modulus of elasticity. Polyacrylonitrile is a high-performance polymer that unlike others has the capability to form highly oriented molecular structure when subjected to a low temperature heat treatment. It has applications in ultra-filtration membranes, hollow fibers for reverse osmosis and fibers for textile. It is also pre-cursor material for the manufacture of carbon fibers which are characterized by high stiffness, high tensile strength, low weight, high chemical resistance, high temperature tolerance and low thermal expansion. In this study, a polyimide blend containing different weight percentages of polyacrylonitrile (0.1, 0.5, 1, 5 and 10 wt%) was fabricated into thin films and characterized for thermal properties using Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC). Structural and mechanical properties were evaluated using Fourier Transform Infrared Spectroscopy (FTIR) and Dynamic Mechanical Analysis (DMA), respectively. Morphology was studied using an Optical Microscope. From FTIR, the degree of Imidization of the blend was found to be 97.5%. Tg of the copolymer was calculated to be ~370ºC from the tan d peak obtained from DMA. While the 10wt% PAN/PI blend exhibits the highest Tg, the 1% exhibits the highest damping ability. Rate of change of enthalpy was calculated using Differential Scanning Calorimetry which shows that increasing the content of PAN resulted in a decrease in heat release. Percentage mass retained and char retention calculations wer (open full item for complete abstract)

Committee: Jude Iroh Ph.D. (Committee Chair); Jonathan Nickels Ph.D. (Committee Member); Yoonjee Park Ph.D. (Committee Member) Subjects: Polymers

Master of Science, University of Akron, 2019, Mechanical Engineering

There is a fast-growing demand for electrospun nanofibers as the choice materials for several technological applications. They typically have large surface area to volume ratio, high porosity meshes, small pore size distribution, structural strength, lightweight, and toughness, all of which enhances their mechanical properties. The nano-scale mechanical behavior of the material, particularly those properties that may influence performance of components made from these materials were investigated. Single electrospun PVDF nanofiber samples were tested for monotonic micro-tensile, stress relaxation, and cyclic stress-strain fatigue behavior. The preliminaries of this study involved electrospinning of PVDF (DMF/ACE 3:1) nanofibers. In the process, a novel method for collection and isolation of single electrospun nanofibers was developed. The single PVDF nanofiber samples showed characteristics non-Hookean behavior and size-dependent properties when pulled for micro-tensile tests. The repetitive stress relaxation of the single electrospun PVDF nanofiber samples showed that the samples sets resulting in decline in cumulative performances. The smaller sized, 0.86μm, single fiber displayed better stress relaxation capability when compared to the 1.07μm sample. The S-N plots obtained from the cyclic stress-strain showed that larger sized PVDF single nanofiber samples, which have higher yield strength, displayed higher S-N curve when compared to the smaller sized samples. The manner of failure and mechanisms during cyclic stress-straining are rather complex. An analysis of the images after cyclic straining revealed that the samples developed features that may be caused by molecular birefringence or fiber fragmentation.

Committee: Shing-Chung Wong Dr. (Advisor); Todd Blackledge Dr. (Committee Member); Xiaosheng Gao (Committee Member) Subjects: Materials Science; Mechanical Engineering; Polymers

Doctor of Philosophy, The Ohio State University, 2018, Materials Science and Engineering

In this study, the formation, evolution, and failure of dissimilar metal welds (DMWs) involving Grade 91 steel using nickel based filler metals were evaluated. First, the curiosity of stable d ferrite found in the heat affected zone (HAZ) of Grade 91 DMWs was investigated since this phase was not present in the HAZ of matching filler metal welds. This difference could have signified a change in the thermal histories of the weld, a change in the chemical potential gradients present, or a combination of both. In the first investigation, it was found that the thermo-mechanical properties of the nickel based filler metal contributed to longer dwell times within the temperature range of stable d ferrite within the HAZ as compared to the autogenous and matching filler metal welds. This occurred because solidification temperature range of nickel based filler metals overlaps the stable d ferrite temperature range and because of the lower thermal conductivity of the nickel based filler metal. These factors enabled carbide dissolution and carbon diffusion, if the presence of a chemical potential gradient existed. Since these welds involved steel base metal and nickel based filler metals, the chemical potential gradients were relevant and were also investigated. The effect of the chemical potential gradient across the dissimilar fusion boundary was also investigated. It was found that there was a strong carbon chemical potential gradient between the Grade 91 base material and the nickel based filler metal caused by a difference in carbon concentration and carbide forming elements. A diffusion simulation was used to predict the magnitude of carbon migration during welding, which resulted in a carbon depleted HAZ. Carbon depletion in the HAZ stabilized the d ferrite phase, shown through statistical analysis of the hardness distribution and a strong correlation between the carbon concentration and amount of d ferrite found in the HAZ. A mechanism was proposed for the (open full item for complete abstract)

Committee: Boian Alexandrov (Advisor); Michael Mills (Advisor); Stephen Niezgoda (Committee Member) Subjects: Engineering; Materials Science

MS, University of Cincinnati, 2018, Engineering and Applied Science: Materials Science

The microstructure and stress states bestowed by the manufacturing process administer the reliability and performance of each component in its final application. Additive Manufacturing (AM) is the trending process among all the innovative methods to produce uniform distribution of microstructure and properties in the constituent parts in a cost-effective manner. However, most of the fusion based manufacturing techniques possess a drawback in the form of residual stresses developed during the processing stage. This demands for the development of more effective AM methods having the potential for near-net shape manufacturing of the parts with minimized residual stresses which has led to the inception of a novel solid-state AM process named “MELD”. This study investigated the microstructure and properties developed in the multi-layer Alloy 600 deposit on 304L stainless steel manufactured by MELD process. Unlike other fusion based AM processes, MELD showed a compressive residual stress (~ -380 MPa) on the surface of the deposited material. The average hardness of the deposit (~ 3.29 GPa) was comparable with that of Alloy 600 manufactured by other AM processes. Additionally, a localized increase in the hardness could be observed at the interfaces between two subsequent layers which was attributed to the grain refinement resulting from dynamic recrystallization in the interfacial areas during the MELD process. Large amount of carbide precipitates formed during the recrystallization at the interface restricted the grains size by pinning them together. High temperature in areas away from interface caused dissolution of carbides leading to grain coarsening. This trend of grains size and carbide precipitates was repeated in each of the deposited layers. The point and space group of the carbide precipitate was determined from TEM analysis. The deposit possessed very low dislocation density and hence low plasticity. Though, the distribution of sub-grains and low angle bounda (open full item for complete abstract)

Committee: Vijay Vasuedevan Ph.D. (Committee Chair); Ashley Pazy Puenta Ph.D. (Committee Member); Matthew Steiner Ph.D. (Committee Member) Subjects: Materials Science

Doctor of Philosophy, University of Akron, 2018, Polymer Science

Since the early 1960s, synthetic biodegradable polymers have been widely used in biomedical applications due to their large chemical diversity and the reproducible properties. However, the local acidification during degradation has shown to cause significant inflammation that can lead to device or implant failure. It is necessary to design new biodegradable polymer systems that do not cause local acidosis during degradation. To facilitate this requirement, Becker group has developed the amino acid-based poly(ester urea)s. These polymers are semi-crystalline. Their hydrolysis byproducts are non-toxic and can be self-buffered by the presence of the urea linkage at each repeat unit. In addition, there is a tremendous physical and chemical landscape that is available for exploration by using different natural amino acids with different pendant groups and different diols. This dissertation outlines our efforts to develop biodegradable polymers with tunable mechanical properties, degradation rates, and bioactivity. We varied the diol chain length (Chapter 3), branch density (Chapter 4), bioceramic contents (Chapter 5) in the poly(ester urea) system; cis/trans ratio (Chapter 6) in the biodegradable elastomer system and studied how these subtle structural differences would influence the mechanical properties and water uptake ability. Based on their tunable physical properties, these materials can be selected and used for various biomedical applications (Chapter 7).

Committee: Matthew L. Becker Ph.D. (Advisor); Bryan Vogt Ph.D. (Committee Chair); Yu Zhu Ph.D. (Committee Member); Amis J. Eric Ph.D. (Committee Member); Chrys Wesdemiotis Ph.D. (Committee Member) Subjects: Biomedical Engineering; Materials Science; Plastics; Polymer Chemistry; Polymers

Doctor of Philosophy, Case Western Reserve University, 2016, Biomedical Engineering

Significant advancements in biodegradable polymeric materials have been made for numerous applications including tissue engineering, regenerative medicine and drug delivery. The functions of these polymers within each application often rely on controllable polymer degradation and erosion, yet the process has proven difficult to measure in vivo. Traditional methods for investigating polymer erosion and degradation are destructive, hampering accurate longitudinal measurement of the samples in the same subject. To overcome this limitation we have explored the use of ultrasound elastography imaging as a tool to nondestructively measure strain of poly(lactic-co-glycolic acid) (PLGA) phase sensitive in situ forming implants which changes with progressive loss of structural integrity resulting from polymer erosion. In order to better employ this technology, ultrasound elastography imaging was first characterized and validated by comparing to the gold standard unconfined compression testing of PDMS samples with different Young's moduli. The detection limit as well as detectable difference of this technique were identified. This imaging system was also optimized to scan stiffer polymeric biomaterials. Using this tool, we investigated erosion kinetics of implants comprised of three different PLGA molecular weights in vitro and in vivo. The in vitro environment was created using a novel polyacrylamide based tissue mimicking phantom while the in vivo experiment was performed subcutaneously using a rat abdominal model. A strong linear relationship independent of polymer molecular weight was found between average strain values and erosion values in both the in vitro and in vivo environment. Results support the use of a mechanical stiffness based predicative model for longitudinal monitoring of material erosion and highlight the use of ultrasound elastography as a nondestructive tool for measuring polymer erosion kinetics.

Committee: Horst von Recum (Committee Chair); Agata Exner (Advisor); Stuart Rowan (Committee Member); Joseph Mansour (Committee Member); Anant Madabhushi (Committee Member) Subjects: Biomedical Engineering; Biomedical Research; Polymers

Master of Sciences (Engineering), Case Western Reserve University, 2014, Materials Science and Engineering

In this study, the variations in mechanical properties and thermal stability of Ni-Co-Ta-based metallic glasses have been analyzed. Three different chemistries of metallic glass ribbons were analyzed: Ni45Ta35Co20, Ni40Ta35Co20Nb5, and Ni30Ta35Co30Nb5. These alloys possess very high density (approximately 11.5g/cm3) and very high strength (e.g. > 3 GPa). Differential scanning calorimetry (DSC) and x-ray diffraction (XRD) were used to characterize the amorphicity of the ribbons. Mechanical properties were measured via a combination of Vickers hardness, bending strength, and tensile strength for each chemistry. At least 50 tests were conducted for each chemistry and each test technique in order to quantify the variability of properties using both 2- and 3-parameter Weibull statistics. The variability in properties and their source(s) were compared to that of other engineering materials, while the nature of deformation via shear bands as well as fracture surface features have been determined using scanning electron microscopy (SEM).

Committee: John Lewandowski (Advisor) Subjects: Materials Science

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

Micromechanical crystal plasticity finite element simulations of the response of synthetic titanium microstructures are carried out with the goal of quantifying the effect of microstructure on mechanical properties. Two separate materials are studied: (1) an alpha-beta Ti-6Al-4V material and (2) a highly-textured, rolled alpha Ti-3Al-2.5V sheet material. Performing accurate finite element analyses begins with accurate image-based characterization of the morphological and crystallographic features of the materials at the microstructural scale. Then, statistically equivalent representative 3D microstructures are built and meshes are generated for crystal plasticity based finite element method (CPFEM) analysis. For the Ti-3Al-2.5V material, experimental results from the displacement controlled mechanical testing of dog bone shaped, rolled specimens are used for the calibration of elastic parameters as well as anisotropic crystal plasticity parameters. The inspection of micrographs of the rolled material showed elongated grain shapes which led to the updating of the crystal plasticity model to include grain aspect ratio dependence on the Hall-Petch size effect--an update of a previous size effect model which assumed spherical grains. Model validation is achieved by comparing load controlled experimental results with simulated creep results. For the Ti-6Al-4V material, the robust and validated analysis tool is used to perform sensitivity analyses and a quantitative understanding of how individual microstructural parameters affect the mechanical response properties of the alloy is developed. Functional dependencies are proposed that directly connect the metal's microstructural features to creep response, yield strength response, and tensile response.

Committee: Somnath Ghosh Dr. (Advisor); June Lee Dr. (Committee Member); Reji John Dr. (Committee Member) Subjects: Aerospace Materials; Engineering; Materials Science; Mechanical Engineering; Mechanics

Doctor of Philosophy, The Ohio State University, 2008, Industrial and Systems Engineering

Die Casting dies and machines are high performance products that are subjected to clamp load, cavity pressure loads and thermal loads during normal operation and the dies and machine deflect under the action of these loads. The ability of the dies to withstand loads and preserve the integrity of the cavity dimensions depends on the structural design of the dies. Die castings dies are expensive products with long production lead times and the structural behavior of the dies has to be predicted at the design stage. The other common problem in die casting is the tie bar load imbalance. The machine clamp load is distributed among the four tie bars depending upon the location of the dies and the location of the cavity center of pressure on the platen. Tie bar load imbalance causes the die parting surface to close unevenly and leads to problems such as flash and premature tie bar failure. The problem is over come by adjusting the length of the tie bars between the machine platens until all the tie bars carry equal loads. Tie bar load predictions are necessary to determine the individual length adjustments needed on each tie bars. Numerical methods such as the finite element method are the most effective way to predict the distortion of the dies and the machine at the design stage. Performing a full FEA during the initial stages of the die design is time consuming and it is not cost effective. So off the shelf design tools such as closed form expressions, design charts and guidelines are needed to make design improvements during the initial stages of the design. In this dissertation research work the relative contribution of the major structural design variables of the die casting die and machine to the mechanical performance of the dies and machines was investigated using computational (FEA) experiments. The maximum parting plane separation was chosen as the performance measure for the structural behavior of the dies and the machine. The computational experiments were des (open full item for complete abstract)

Committee: R. Allen Miller PhD (Advisor); Jerald Brevick PhD (Committee Member); Khalil Kabiri-Bamoradian PhD (Committee Member) Subjects: Industrial Engineering; Mechanical Engineering

Doctor of Philosophy (PhD), Ohio University, 2007, Civil Engineering (Engineering)

The primary objective of this research consisted of incorporating laboratory-determined viscoelastic material properties into a three-dimensional finite element model to accurately simulate the behavior of a perpetual pavement structure subjected to vehicular loading at different pavement temperatures and vehicular speeds. With this finite element model, statistical models that were based on Falling Weight Deflectometer testing were developed to predict the structural response of a perpetual pavement. In this research, the dynamic modulus test was chosen to determine viscoelastic properties of hot-mix-asphalt materials in the laboratory. A 5-term Prony series was used to describe the viscoelastic behavior of hot-mix-asphalt materials. Resilient modulus tests were performed to measure resilient moduli of hot-mix-asphalt mixtures and subgrade soils. All these laboratory-determined material properties were inputted into the developed viscoelastic finite element model to predict pavement response. The developed viscoelastic finite element model was validated by and calibrated to field-measured pavement responses collected at the U.S. 30 perpetual pavement constructed in Wayne County, Ohio. The results demonstrated that the developed viscoelastic finite element model can predict pavement responses accurately. Parametric studies revealed that the developed viscoelastic finite element model performed better in pavement thickness design compared with perpetual-pavement-design-oriented software PerRoad which underestimated pavement responses. Layer modulus variation did not affect pavement response significantly. The ratio maximum-tensile-strain/load was independent of the axle load. The ratio maximum-tensile-strain/speed increased with decreasing in vehicular speeds. A nomograph was developed to correlate the maximum tensile strain to the pavement temperature depending on the thickness of the ODOT302 layer and the aggregate base. Finally, the developed finite element mo (open full item for complete abstract)

Committee: Shad Sargand (Advisor) Subjects: Engineering, Civil

Master of Science (MS), Ohio University, 2000, Mechanical Engineering (Engineering)

Torsion fatigue system for mechanical characterization of materials

Committee: Hajrudin Pasic (Advisor) Subjects: Engineering, Mechanical

Bachelor of Science, Miami University, 2012, School of Engineering and Applied Science - Mechanical Engineering

Magnetorheological elastomers (MREs) are an emerging branch within the smart materials field that consists of hard or soft magnetic particles embedded in a rubber compound. Current applications and research have been focused on changing the stiffness of these materials by applying an external magnetic field. Components of vibration absorbers and base isolation systems that employ this material have shown the capability of offering improved performance over conventional solutions. These particular applications use soft magnetic material; however, MRE materials containing hard magnetic filler materials (those that remain permanently magnetized) were the primary focus of this project and are referred to as H-MREs. When a magnetic field is applied perpendicularly to these particles, the filler particles generate a net torque and these samples can be used as a controlled actuator. Preliminary work has been conducted to characterize these H-MREs (since their properties are significantly different than “soft” MREs) and this work has shown their usefulness in engineering applications. However, unlike comparable smart materials such as piezoelectrics and electroactive polymers (EAP), additional modeling and experimentation needs to be conducted in order to develop usable models and better understand their behavior. The first portion of this paper focuses on developing experimental models to predict the behavior of H-MRE materials as cantilevered beam actuators for use in future applications. Two additional, newer applications for which H-MREs could be useful are energy harvesting and sensing. Sensors are utilized almost everywhere today as they are used to monitor the performance of a system (whether it is fluid flow, vibration measurements, etc.). Piezoelectric materials, those that respond to electric stimuli, and Galfenol, an engineered material similar to MREs, have been studied extensively for their application as self-sensing actuators. It is hypothesized that H-MREs c (open full item for complete abstract)

Committee: Jeong-Hoi Koo PhD (Advisor); Amit Shukla PhD (Committee Member); Kumar Singh PhD (Committee Member) Subjects: Materials Science; Mechanical Engineering

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: