Master of Science (MS), Ohio University, 2022, Civil Engineering (Engineering and Technology)

As stated in the House Bill 62 Transportation Budget in Brief, roughly 5 billion dollars is spent yearly on road pavement construction in the state of Ohio, with a significant chunk for maintenance. Moreover, maintenance activities and their associated costs are increased in the colder regions of the US where damages and distress on roadways are associated to the Low Temperature Cracking (LTC) phenomena or at least in combination with other distress like rutting and fatigue cracking. Thermally induced internal cracking is a mechanism that occurs under low temperature conditions. Akentuna et al. (2017) postulated that the differential in Coefficient of Thermal Contraction (CTC) values in asphalt binder and aggregate gives rise to thermally induced internal cracking at low temperatures. Owing to its potential significance and effect on LTC modeling, this study investigated the thermally induced thermal cracking phenomena using the Indirect Tensile (IDT) test. The IDT test was selected since it is the test procedure used in fracture property investigation in the AASHTOWare Pavement Mechanistic Empirical (ME) Design program for low temperature cracking modeling. In addition, a study on the effect of loading rate and temperature on asphalt mixtures during the ITS test was also investigated. Although thermally induced internal cracking was observed by Li et al. (2007) using the acoustic emissions test and Behnia et al. (2014) using the Disc-shaped Compact Test (DCT), its quantified effect has not been studied. The results garnered from this study validated the occurrence of thermally induced internal cracking, evidenced by significant reduction in IDT peak strengths and energy at peak stress to averaged magnitudes of 4% and 12% respectively. The second objective of this study on varying loading rate and temperature during the IDT strength tests proved that the standard test loading rate of 12.5mm/min rate was too fast and not representative of f (open full item for complete abstract)

Committee: Issam Khoury Dr. (Advisor); Bhaven Naik Dr. (Committee Member); Benjamin Sperry Dr. (Committee Member); Eung Lee Dr. (Committee Member) Subjects: Civil Engineering

Master of Science, The Ohio State University, 2020, Mechanical Engineering

Sheet metal forming or stamping is the process of plastically deforming sheet blanks into a complex-shaped part, usually without significant change in sheet thickness and surface characteristics. As the problem of climate change is becoming more prominent, the emission standards are becoming more stringent for automobiles. This has driven automotive companies towards light weighting while maintaining the structural integrity of the vehicle. Tailor Welded Blanks (TWBs) have been introduced in the automotive industry to aid in reducing the weight while maintaining the structural performance of stamped parts. Laser welding is the most conventional method for developing TWB. The mechanical behavior of tailor-welded blanks differs from the base materials (materials being welded together) due to the welding. Therefore, comprehensive understanding of deformation behavior and formability of TWBs is essential. The objective of this study is to develop a practical methodology for evaluating the formability of TWBs. This study focuses on TWBs with sheets of same thickness on both sides of weld. In this study, same thickness welded blank (1.2 mm to 1.2 mm) of Galvannealed Draw Quality Aluminium Killed (GNDQAK) steel is evaluated using the tensile test, limiting dome height test, viscous pressure bulge test and plane strain loading condition. Mechanical properties of the material is obtained through the tensile test. The hardening curve for the weld zone and heat affected zone (HAZ) is approximated by comparing the hardness of these zones compared to the base material. Numerical models are developed to simulate material behavior in each of these tests. To improve the simulation accuracy, various material models for the base material, the HAZ, and the weld zone are considered. The most accurate model has been used for simulating the behavior of the welded blank in the hat bending and square cup drawing process. Tensile test experiments of the monolithic and welded coupons are c (open full item for complete abstract)

Committee: Taylan Altan (Advisor); Yannis Korkolis (Committee Member) Subjects: Aerospace Engineering; Industrial Engineering; Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2019, Industrial and Systems Engineering

Edge fracture, defined simply as fracture originated from the edge, is a common problem in sheet metal forming, especially when forming Advanced High Strength Steels (AHSS). The increase of AHSS in the automotive industry has derived into substantial efforts in order to predict and prevent the edge fracture phenomenon. Nearly every sheet metal forming operation includes cutting of the material at some point and, depending on the cutting process, the damage produced at the edge reduces its formability in subsequent operations. The edge fracture has been approached from various perspectives: observation of the cut edges in order to correlate their geometries to edge fracture occurrence, methods to evaluate edge stretchability, Finite Element (FE) simulations to predict it, design of new cutting methods (i.e. tool geometries or configurations) or post-processing of the edge to eliminate residual stresses (i.e. annealing or machining). Nevertheless, there is not a consensus in the field regarding which ones are the most important factors that should be considered in sheet metal cutting. Furthermore, researchers, very often, overlook practical parameters during laboratory test (e.g. non-uniform cutting clearances, tool wear, etc.); hence, these laboratory tests, generally, do not represent the cutting conditions found in the practice. This project aims to propose guidelines that could be considered to evaluate, maintain and improve a given cutting process for a required edge stretchability. In order to achieve this objective, four cases studies, which include most of the of the typical challenges in sheet metal cutting, were conducted: trimming along a straight line, piercing of a round hole, blanking of an irregular geometry and use of shaving (two-stage cutting) to improve edge stretchability. Chapter 1 of this study gives a brief introduction to the edge fracture problem and the available sheet metal cutting techniques. Chapter 2 summarizes the research objec (open full item for complete abstract)

Committee: Taylan Altan Dr. (Advisor) Subjects: Industrial Engineering; Mechanical Engineering

Doctor of Philosophy (PhD), Ohio University, 2018, Civil Engineering (Engineering and Technology)

In recent years, the incorporation of recycled material in the production of plastic pipes has gradually increased. With this new development, the federal government were considering the possibilities of allowing corrugated high-density polyethylene (HDPE) pipes manufactured with post-consumer recycled (PCR) materials installed as culverts under major highways, despite the fact that they may contain impurities and their long-term behavior is still not fully understood. This dissertation was part of the NCHRP Report 870 (Pluimer, 2018), which led to a new revision in AASHTO M-294. This new revision allows HDPE pipes to be manufactured with either virgin or recycled materials. This dissertation presents a test program recently completed at Ohio University, in which corrugated HDPE pipes with varied post-consumer recycled (PCR) material contents were subjected to a forced long-term constant vertical deflection of 20%. Eight HDPE pipe specimens having inside diameter of either 610 mm (24 in) or 762 mm (30 in) were kept in a compressed state in the laboratory for two years. The maximum tensile strain was found to be about 3% for all the pipes. No cracks were seen in the 0% PCR and the 49% PCR pipes during the 2-year duration. However, the 98% PCR pipe developed longitudinal cracks at the crown position inside after 101 days and additional longitudinal cracks at the springline position outside after 131 days. To predict the long-term behavior of HDPE drainage pipes, coupon specimens with 0%, 49%, and 98% post-consumer recycled (PCR) materials were loaded incrementally in tension according to the stepped isostress method (SSM) to establish their master creep curves. A reference stress of 15% ultimate tensile strength was used with a dwell time of 24 hours. The 0% and 49% PCR specimens elongated by more than 600%, whereas the 98% PCR specimen elongated little and ruptured within a few minutes after adding the final load. The trend of the SSM's shift factors in terms o (open full item for complete abstract)

Committee: Teruhisa Masada (Advisor); Shad Sargand (Committee Member); Issam Khoury (Committee Member); Sergio Lopez-Permouth (Committee Member); Xiong Yu (Committee Member) Subjects: Civil Engineering; Geotechnology

Doctor of Philosophy, University of Akron, 2017, Polymer Engineering

The use of structural adhesives has an increasing demand as a joining technique in the automotive industry due to the possibility of reduction in vehicle weight, fuel consumption and CO2 emission. By using load bearing structural adhesives, high-strength and tough structures can also be incorporated into automotive bodies to create impact resistant automobiles with improved crashworthiness. Consequently, it is important to understand mechanical response of adhesives subjected to crash loading in order to develop mechanical models with predictive capabilities. The focus of our study was to identify physical properties of different toughened structural adhesives and identify/develop an elastic-viscoelastic-plastic model as a function of loading rate by using Ludwik type equations to be able to predict adhesive behavior at higher loading rates and to make cars more crashworthy. We also measured and analyzed the fracture properties of toughened structural adhesives at different fracture modes to unveil their mechanical behavior more precisely as related to their crashworthiness. First, eight different commercial toughened epoxy structural adhesives were characterized to provide detailed information about the constituents of adhesives. The main crystalline inorganic ingredients were found as calcite and calcium oxide for all types of adhesives. The total amount of inorganic fillers was found to be different in each adhesive. Second, material parameters of four model adhesives were determined via tensile test and via Single Lap Joint (SLJ) test in shear. Stress-strain behavior of adhesives presented typical viscoelastic behavior in which linear–elastic behavior was observed first followed by viscoelastic behavior with strain rate sensitivity. The strain rate sensitivity was described by incorporating Ludwik type equations into our modelling process. Multiple elastic limit (yield) stresses and strains indicating bilinear-elastic behavior were identified for all adhesi (open full item for complete abstract)

Committee: Erol Sancaktar Dr. (Advisor); Xiong Gong Dr. (Committee Chair); Sadhan J. Jana Dr. (Committee Member); Darrell Reneker Dr. (Committee Member); Wieslaw K. Binienda Dr. (Committee Member) Subjects: Polymers

Master of Science, The Ohio State University, 2016, Welding Engineering

Pipes of solid solution strengthened Ni-based alloys, as Alloy 826 and Alloy 800H, have been used for high temperature service in once through steam generators (OSTGs) on off-shore platforms. The oil and gas industry is seeking to increase service temperature, improve service reliability, and extend service life to 40 years of such installations. Alloy 230 has better-high temperature stability and mechanical properties, and higher service temperature than Alloys 825 and 800H, and is therefore considered as a potential replacement of these alloys in newly built OTSGs. However, the weldability and the high temperature service behavior in welds of Alloy 230 have not been thoroughly investigated yet. This study is a comprehensive comparative research focused on susceptibility to solidification cracking and stress relief cracking in Alloys 800H, 825, and 230. To evaluate the solidification behavior and solidification cracking susceptibility in these alloys, the Cast Pin Tear Test (CPTT), thermodynamic simulations with Thermo-Calc, and the technique of Single-Sensor Differential Analysis (SS-DTA) were used. The results revealed that Alloy 230 and Alloy 825 were more resistant to solidification cracking than Alloy 800H, due to narrower solidification temperature range and crack back filling with eutectic constituents. The OSU Stress Relief Cracking (SRC) Test was applied to evaluate the susceptibility to stress relief cracking in autogenous gas tungsten arc welds of the investigated alloys. None of the three alloys failed by stress relief cracking mechanism while loaded at stress equal to 90% of the high temperature yield strength at 650 oC for 8 hours.. Alloys 825 and 800H showed significant amount of stress relief, while Alloy 230 sustained the applied load at 650C with almost no stress relief. Tensile testing at 650 oC after the 8 hours SRC test showed that the autogenous weld in Alloy 230 had significantly higher yield and tensile strength and slightly lower el (open full item for complete abstract)

Committee: Boian Alexandrov (Advisor); Avraham Benatar (Advisor) Subjects: Materials Science; Metallurgy

Master of Science, University of Akron, 2016, Polymer Engineering

In this study, the relationship between an eco-friendly filler, fly ash, and the properties of Styrene-Butadiene Rubber (SBR) - based compounds was investigated. Rubber compounds were produced by internal mixer and curing characteristics were evaluated. The total content of filler was constant and the content of fly ash increased from 0 to 10 phr. In the evaluation of the rubber compounds, the main focus was the mechanical properties and adhesion of the SBR compounds. Adhesion between these compounds and steel wire reinforcement was measured for assessing efficacy of adding fly ash to the rubber compounds in tire applications. There were two stages of this program: the first stage involved selecting the filler which could improve the mechanical properties (elongation at break, tensile strength, modulus at 100% strain and 2% strain level) of rubber compounds; the next stage involved combining precipitated silica with fly ash to improve the properties of rubber compounds. In order to gain better properties, ball mill treatment was used to change the morphology of the particles of fly ash by reduction to smaller size. The comparisons of untreated rubber compounds, ball mill treated rubber compounds, and rubber compounds containing different fillers were accomplished subsequently. In the result, the rubber compounds contained precipitated silica, carbon black and fly ash filler exhibited higher tensile strength, elongation at break, and adhesion and attributed to effective filler dispersion as well as the reinforcing effect of silica. These conclusions were supported by the scanning electron microscopy (SEM) and swelling tests.

Committee: Erol Sancaktar (Advisor); Sadhan Jana (Committee Chair); Shing-Chung Wong (Committee Member) Subjects: Materials Science; Polymers

Master of Science, The Ohio State University, 2009, Industrial and Systems Engineering

The increase in using Advanced High Strength Steel (AHSS) and aluminum sheet materials is accompanied by many challenges in forming these alloys due to their unique mechanical properties and/or low formability. Therefore, developing a fundamental understanding of the mechanical properties of AHSS, as compared to conventional Draw Quality Steel (DQS), is critical to successful process/ tools design. Also, alternative forming operations, such as warm forming or sheet hydroforming, are potential solutions for the low formability problem of aluminum alloys. In this study, room temperature uniaxial tensile and biaxial Viscous Pressure Bulge (VPB) tests were conducted for five AHSS sheet materials; DP 600, DP 780, DP 780-CR, DP 780-HY, and TRIP 780, and the resulting flow stress curves were compared. Strain ratios (R-values) were also determined in the tensile test and used to correct the biaxial flow stress curves for anisotropy. The pressure vs. dome height raw data in the VPB test was extrapolated to the burst pressure to obtain the flow stress curve up to fracture. Results of this work show that flow stress data can be obtained to higher strain values under biaxial state of stress. Moreover, it was observed that some materials behave differently if subjected to different state of stress. These two conclusions, and the fact that the state of stress in actual stamping processes is almost always biaxial, suggest that the bulge test is a more suitable test for obtaining the flow stress of AHSS sheet materials to be used as an input to FE models. An alternative methodology for obtaining the flow stress from the bulge test data, based on FE-optimization, was also applied and shown to work well for the AHSS sheet materials tested. Elevated temperature bulge tests were made for three aluminum alloys; AA5754-O, AA5182-O, and AA3003-O, using a special machine where the tools and specimen are submerged in a fluid heated to the required temperature. Several challenges were faced (open full item for complete abstract)

Committee: Taylan Altan (Advisor); Jerald Brevick (Committee Member) Subjects: Automotive Materials; Engineering; Industrial Engineering; Materials Science; Mechanical Engineering

Doctor of Philosophy, Case Western Reserve University, 2024, Chemistry

Replacing inorganic semiconductors with organic semiconductors (OSCs) in electronic devices is a promising way to make cheap, light-weight, and flexible electronic devices. Currently, charge carrier mobility of OSCs rivals that of amorphous Si, however, they suffer from mechanical brittleness that limit their application. Simultaneously improving mechanical properties while maintaining charge carrier mobility is challenging since both are orthogonally affected by film morphology, which is affected by the chemical structure. To understand how to optimize both properties it is thus imperative to systematically study chemical structure-property relationship. Regioregular poly(3-alkylthiophene)s (P3AT) are easy to synthesize conjugated polymers (CPs) with good electrical properties, but tend to be brittle, limiting their application. In chapter 2 and 3, we functionalize the side chains of P3ATs to improve their mechanical properties. In chapter 2, we investigate incorporating ester groups in the side chains of poly(3-hexylthiophene) (P3HT) and poly(3-dodecylthiophene) (P3DDT) six carbons away from the polymer backbone. The best combination of robustness and charge carrier mobility is obtained for the P3HT random copolymer with 10\% ester-functionalized side chain: a high fracture strain (296%) combined with a high tensile strength (3.90.6 MPa) resulted in a large toughness (9030 J/m3). This is achieved while maintaining the same high charge carrier mobility as a similar MW P3HT (0.120.01 cm2 V-1 s-1). Side chain modifications do not improve mechanical properties of P3DDT-based copolymers as much, most likely because the longer dodecyl side chains can crystallize, resulting in microphase separation of the side chain and main chain. As a result, side chain modification has little plasticizing effect on the P3DDT main chain for 0-50% ester content copolymers. These results demonstrate that side chain modification with ester-functionality can optimize both mechani (open full item for complete abstract)

Committee: Genevieve Sauve (Advisor); Clemens Burda (Committee Chair); Valentin Rodionov (Committee Member); John Protasiewicz (Committee Member); Shane Parker (Committee Member) Subjects: Chemistry

Master of Science in Engineering, Youngstown State University, 2023, Department of Mechanical, Industrial and Manufacturing Engineering

This thesis presents an analysis of linear friction welding of dissimilar metals, specifically aluminum and copper, with a zinc interlayer. The welding of aluminum and copper is significant for heat transfer and electrical applications, as these metals are commonly used. Traditional fusion welding methods are ineffective due to the metals' differing melting points, making solid-state joining processes like friction welding preferable. The main objective of this research is to address the challenges in welding copper and aluminum using linear friction welding and to improve the strength of the resulting weld. One major issue encountered during welding is the formation of brittle intermetallic compounds at the interface. To overcome this problem, an interlayer of zinc is used during the welding process. This study investigates the impact of two different thicknesses of the zinc interlayer, namely 0.07 mm and 0.2 mm. The welding process was conducted using a 20-ton vertical oscillator welding machine. The resulting welds were subjected to various analyses, including tensile tests, hardness tests, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). Successful welding was achieved both with and without the interlayer. There was no significant difference in the ultimate tensile strength (UTS) between the two interlayer thicknesses, but the UTS of the samples with interlayers showed a 28% increase compared to the samples without interlayers. The hardness at the junction without an interlayer was higher (180 HV) than the hardness with an interlayer (159 HV). SEM images revealed cracks in the welding regions without interlayers, indicating the formation of brittle intermetallic compounds at the junction. Thermal analysis was also performed to predict the temperature at the junction during welding, utilizing parameters such as frequency, amplitude, and time. The use of interlayer materials was found to enhance the tensile strength of the (open full item for complete abstract)

Committee: Jae Joong Ryu PhD (Advisor); C. Virgil Solomon PhD (Committee Member); Kyosung Choo PhD (Committee Member) Subjects: Materials Science; Mechanical Engineering

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

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

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

Doctor of Philosophy (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

PhD, University of Cincinnati, 2020, Engineering and Applied Science: Materials Science

Silicon has been widely used in various electronic and optoelectronic devices for its excellent properties. As temperature increases, silicon changes from brittle to ductile at around 545 The brittle-to-ductile transition (BDT) behavior has been observed with silicon nanostructures at room temperature. The molecular dynamics method has been used to investigate the size-dependence in BDT. In the literature, different transition sizes have been reported based on different potential models. Apart from potentials, simulation types (constant energy vs. constant temperature) and boundary conditions can also influence the behaviors of silicon nanostructures. Furthermore, the oxidization is another key factor that can affect the properties of silicon nanostructures. But the role of the oxidization in the BDT of silicon nanostructures has been rarely investigated. Therefore, this dissertation studies the BDT of [110]- oriented single crystalline Si nanowires in atomic level with focus on the influence of three factors: potential models, simulation types and boundary conditions, and the oxidization of silicon nanowires. In Chapters I to II, some backgrounds and literature review on the BDT of silicon and simulation methods are given. Chapter III investigates the impact of three different modified embedded-atom-method (MEAM) potentials, referred to as Baskes, Lee, and Lee-modified, on BDT. Uniaxial tensile tests of silicon nanowires are conducted by considering several key parameters such as size, temperature, and strain rate. The ductile failure probability parameter is introduced to quantify the failure behaviors of nanowires. Overall, the ductile failure probability increases with decreasing size and increasing temperature. The Baskes nanowires exhibit the most ductile failures whereas most Lee-modified nanowires fail in brittle mode. The Lee model shows intermediate levels of ductile failure behavior. Using the same potentials as in Chapter III, Chapter IV investig (open full item for complete abstract)

Committee: Woo Kyun Kim Ph.D. (Committee Chair); Gregory Beaucage Ph.D. (Committee Member); Yao Fu Ph.D. (Committee Member); Vesselin Shanov Ph.D. (Committee Member) Subjects: Materials Science

Master of Science (MS), Ohio University, 2020, Mechanical Engineering (Engineering and Technology)

Fatigue failures are sudden and catastrophic, and for critical parts must be prevented through proper design. Fatigue testing of materials yields data critical for proper design but takes large spans of testing time to complete with conventional methods. Therefore, high speed fatigue testing that produces quality data is advantageous for reducing costs and time. However, it has been shown that testing speeds may affect material performance, both in static tensile testing and dynamic fatigue testing. The effect of strain rate on material performance in static tensile testing and how it relates to fatigue testing performance at commensurate strain rates was the primary objective for this thesis work for sheet Ti-6Al-4V and Inconel 718. Implementing a vibration-driven, fully reversed bending fatigue test protocol leveraging high speed testing capability, a comparable forced displacement bending fatigue test protocol, and a high speed tensile test protocol implementing Digital Image Correlation (DIC), stress versus strain data and S-N curve data was acquired to examine two strain-rates of fatigue and tensile testing. Higher ultimate tensile strengths were observed in high strain rate tests as compared to low strain rate tests, 4.23% higher for Ti-6Al-4V and 1.91% for Inconel 718. Ti-6Al-4V exhibited higher fatigue strength in high speed tests than low speed, but Inconel 718 exhibited lower fatigue strength at high speeds as compared to low speeds.

Committee: Timothy Cyders Dr. (Advisor); Brian Wisner Dr. (Committee Member); Young David Dr. (Committee Member) Subjects: Aerospace Engineering; Aerospace Materials; Engineering; Experiments; Mechanical Engineering; Systems Design

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

Magnesium has been considered an excellent candidate as lightweight structural material for many years, but the low ductility caused by its plastic deformation mechanism has always been a limitation of extensive application.In this work, we use molecular dynamics approach to simulate tensile test on single crystal and polycrystalline magnesium to investigate its tensile behavior and plastic deformation mechanism. In each tensile simulation on single crystal magnesium, we applied extensions with constant strain rate along each of the [1-210], [10-10] and [0001] direction at the temperature of 100 K, 200 K, 300 K, 400K and 500 K. From these simulation, magnesium nanocrystals has shown strong anisotropy that the loading direction significantly influence the tensile strength as well as the deformation mechanism. At the same time, temperature plays an important role during the plastic deformation of magnesium. We also performed tension simulations on polycrystalline magnesium nanocrystals with number of grains equal to 1, 2, 3, 4 and 5 which are randomly generated using Voronoi tessellation. These simulations prove that the grain boundaries in polycrystalline models play a dominant role affecting the tensile behavior of magnesium. Grain boundaries affect the tensile strength, the formation of cracks and they act as source for slips and deformation twins.

Committee: Woo Kyun Kim Ph.D. (Committee Chair); Vesselin Shanov Ph.D. (Committee Member); Kumar Vemaganti Ph.D. (Committee Member) Subjects: Materials Science

Master of Science (MS), Ohio University, 2007, Civil Engineering (Engineering)

Two long life pavement test sections were completed along US Route 30 in Wayne County, OH, as part of the Wooster by-pass, in the fall of 2005. This project represents a collaborative effort between the Ohio Department of Transportation (ODOT) and both the asphalt concrete paving and Portland cement concrete paving industries with the purpose of evaluating the performance of these novel pavements. The unique perpetual asphalt pavement concept is featured in one direction of the project, while a long lasting Portland cement concrete pavement was constructed in the other direction. The test pavements were instrumented for dynamic response parameters and subjected to controlled load vehicle tests. Results indicate that the asphalt concrete pavement exhibited “perpetual” characteristics under most loading conditions. Non-destructive tests and the determination of the mechanical properties also helped to evaluate the long life characteristics of the two pavement designs.

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

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

ElectroStatic Precipitators (ESP) are widely used in coal fired power plants for control of particulate matter and other toxic gases. Traditionally, ESP's used metal plates as collecting surfaces for capture of particles in flue gas. However, back corona and re-entrainment of particles into flue gases hinder with the performance of ESP in collection of fine particulate matter (PM2.5). Metal plate ESP's also suffer from problems due to corrosion. Researchers at Ohio University developed a patented wet membrane based ESP to overcomes these difficulties. Wet membrane based ESP replaces the metal collecting surfaces with woven fabrics. Omnisil 1000, a silica fabric (98.5% silica), is found to be suitable for this application. The replacement of metal collecting plates with fabric requires application of tensile loads on the fabric during operation of ESP. A study of tensile and creep behavior is presented. A test facility for uniaxial tension and creep testing of Omnisil fabric is developed. The uniaxial tensile behavior of the fabric is typical to plain woven fabrics and the failure strength bears a linear relation to fabric width. The creep elongation of the fabric is negligible in the experimental conditions.

Committee: David Bayless (Advisor) Subjects: Engineering, Mechanical

Doctor of Philosophy, Case Western Reserve University, 2012, EMC - Mechanical Engineering

This thesis consists of three parts. First, the numerical methods for Equation of Phonon Radiative Transport (EPRT) in 3D domains are derived and implemented by COMSOL PDE module based on Equation of Phonon Radiative Transport and Boltzmann Transport Equation theory, which can be used to analyze the phonon dominant thermal conduction problems in multiple-domain nano-structures. Second, a new symmetric in-situ nano-scale tensile test MEMS device is presented, which can continuously observe the nano-specimen at large strain in SEM. The optimum platinum EBID clamping operation parameters are reported, and its strength is estimated per experiment results on polyaniline non-wire. Finally, the high strain rate dynamic properties of two nano-grained aluminum alloy groups are investigated by Split-Hopkinson-Pressure-Bar tests, which demonstrate the material dynamic flow strength enhancement by adding ceramic nano-particles.

Committee: Vikas Prakash PhD (Advisor); Iwan Alexander Dept Chair (Committee Member); Jaikrishnan Kadambi Dept Asso. Chair (Committee Member); Xiong (Bill) Yu PhD (Committee Member); Vikas Prakash PhD (Committee Chair) Subjects: Materials Science; Nanoscience; Nanotechnology

Master of Sciences (Engineering), Case Western Reserve University, 2011, Materials Science and Engineering

A new tensile strength test was developed successfully that avoided bending force issues, ice samples slipping problem, ice sample misalignment issues, while ensuring uniform application of loading force. Ice samples were prepared using distilled water, rain water, tap water, and water obtained from Lake Erie. The tensile adhesive strengths of the distilled ice/substrate materials interface were 1.19±0.29MPa, 0.76±0.11MPa, and 0.59±0.19MPa to stainless steel, a polyurethane wind turbine blade top coat, and epoxy primer coating, respectively. In an unexpected result, the tensile adhesive strengths of the Lake Erie ice/substrate materials interface were statistically significantly lower at 0.32±0.05MPa, 0.34±0.08MPa, and 0.27±0.07MPa to stainless steel, polyurethane top coat, and epoxy primer coating, respectively. The adhesive strength of intentionally doped-saline ice/stainless steel interface decreased when the concentration of sodium chloride or calcium chloride increased. The reduction of saline water ice and Lake Erie ice/wind turbine materials adhesive tensile strength was therefore attributed to the presence of chloride ions.

Committee: David Matthiesen (Advisor) Subjects: Materials Science

Master of Science, University of Akron, 2011, Mechanical Engineering

The history of steel dates back to the 17th century and has been instrumental in the betterment of every aspect of our lives ever since, from the pin that holds the paper together to the automobile that takes us to our destination steel touch everyone every day. Pathbreaking improvements in manufacturing techniques, access to advanced machinery and understanding of factors like heat treatment and corrosion resistance have aided in the advancement in the properties of steel in the last few years. This thesis report will attempt to elaborate upon the specific influence of composition, microstructure, and secondary processing techniques on both the static (uni-axial tensile) and dynamic (impact) properties of the four high strength steels AerMet®100, PremoMetTM290, 300M and TenaxTM 310. The steels were manufactured and marketed for commercial use by CARPENTER TECHNOLOGY, Inc (Reading, PA, USA). The specific heat treatment given to the candidate steels determines its microstructure and resultant mechanical properties spanning both static and dynamic. Test specimens of the steels were precision machined and conformed to standards specified and prescribed by the American Society for Testing Materials (ASTM) for both tensile tests and Charpy V-Notch impact tests. Based on similarity of the secondary processing technique the candidate specialty steels were divided into two groups: (i) AerMet®100 and PremoMetTM290, (ii) 300M and TenaxTM310. The impact toughness response and resultant fracture behavior of the steels were studied at different temperatures ranging from -180°C to +170°C. Tensile tests were performed at room temperature and the final fracture behavior of the candidate steel was established at both the macroscopic and fine microscopic levels. The intrinsic microscopic mechanisms governing the impact toughness, quasi static deformation and final fracture behavior of each of the chosen high strength steels will be elaborated upon in light of the conjoint and mutuall (open full item for complete abstract)

Committee: Dr Tirumalai Srivatsan PhD (Advisor); Craig C. Menzemer Dr. (Committee Member); Gregory Morscher Dr. (Committee Member) Subjects: Mechanical Engineering