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

Age-hardenable 6xxx-series aluminum-magnesium-silicon (Al-Mg-Si) alloys are commonly used in automotive applications due to their high strength-to-weight ratio and their potential for weight savings. However, there is an increased likelihood of corrosion issues due to the chloride-rich environment produced by using road salts in the winter, as well as coupling with more noble materials, such as steels and carbon fiber reinforced polymer (CFRP), when used in conjunction with Al alloys. The combination of a corrosive environment, the residual stresses induced during forming processes, and the possibility of a strong galvanic couple may increase the stress corrosion cracking (SCC) susceptibility of these normally SCC-resistant Al alloys. This research aims to understand the effect of electrochemical potential on the SCC behavior of AA6111 used in automotive applications. The first part of this work examines the effect of polarization on the threshold stress intensity (KTH) and Stage II crack growth rate (da/dtII) during fracture mechanics-based experiments in 0.6 M NaCl to determine the likelihood of galvanic coupling with CFRP increasing the SCC-susceptibility of AA6111 with an automotive paint bake heat treatment (PB). The measured KTH decreases from near fracture toughness values of ~17 MPa√m at the open circuit potential (OCP) to less than 6 MPa√m when anodically polarized to 100 mV above OCP, and da/dtII increases with increasing anodic polarization of 75 to 100 mV above OCP. This indicates that sufficient anodic polarization induces SCC susceptibility in AA6111-PB. The cracking behavior under cathodic polarization was explored to investigate whether SCC reactivates in AA6111-PB. Results at -1300 mVSCE indicate no significant effect of cathodic polarization on SCC. In the second part of this work, the effect of polarization on the crack tip pH of peak-aged (PA) AA6111 under various polarization levels was investigated to directly link changes in SCC resistan (open full item for complete abstract)

Committee: Jenifer (Warner) Locke (Advisor); Eric Schindelholz (Committee Member); Gerald Frankel (Committee Member) Subjects: Engineering; Materials Science

Doctor of Philosophy, The Ohio State University, 2015, Geological Sciences

Polybrominated diphenyl ethers (PBDEs) are a class of brominated flame retardant that is ubiquitous in the environment and detected in a variety of both biotic and abiotic samples. Mounting concern over the last several decades over the toxic effects of PBDEs has resulted in a global cessation in their production. Nonetheless, PBDEs will continue to be detected in the environment due to their emission from ongoing use and recycling of PBDE-containing products. PBDEs are distally transported to the Arctic, but little is known about the fate of these compounds in Arctic surface waters, especially in the presence of dissolved organic matter (DOM). The present study is focused on quantifying the influence of DOM in the binding (i.e. dissolved organic carbon—water partition coefficients, KDOC) and abiotic photodegradation rates, mechanisms, and product formation of PBDEs under environmentally relevant conditions. My results indicate that PBDEs strongly bind to DOM, whereby the measured KDOC were nearly an order of magnitude lower than previously reported values for the same PBDE congeners in soil or commercially available organic matter. The KDOC values measured in the present study range from 103.97 to 105.16 L Kg-1 of organic carbon, which increase with congener hydrophobicity. This association with DOM facilitates PBDE photodegradation, resulting in at least a factor of 2 increase in rate constants for the indirect relative to direct photolysis of BDE-47. Photodegradation rates are strongly positively associated with DOM aromaticity and negatively correlated to dissolved oxygen. As such, photodegradation likely occurs via reduction reactions with excited triplet DOM and is expected to be insensitive to reactive oxygen species. Finally, the efficacy of fluence-based rate constants is explored for the direct comparison of experiments conducted under variable natural and artificial sunlight. Using the irradiance normalization method, discussed in t (open full item for complete abstract)

Committee: Yu-Ping Chin (Advisor); Kristopher McNeill (Committee Member); William B. Lyons (Committee Member); John Lenhart (Committee Member) Subjects: Environmental Science

MS, University of Cincinnati, 2021, Engineering and Applied Science: Mechanical Engineering

Bubble dynamics is integral to many chemical and industrial processes such as aeration, froth floatation, bubble column reactors, fermentation, etc. It becomes imperative to study the growth of bubble formation in order to understand the undergoing processes effectively. Even after eight decades of extensive research, the process of bubble formation is not fully understood, especially the effect of liquid physicochemical properties on bubble size has eluded scientists time and again. The aim of this work is to investigate the complex phenomenon of adiabatic bubble growth from submerged capillaries in liquid pool under constant gas flow rate through a combination of experimental and computational techniques. The influence of cavity/orifice size on bubble departure diameter was studied experimentally. It was observed that for a given liquid, irrespective of the air flow rate, the bubble size increased with increase in orifice size. Also, at low flow rates where the bubble diameter is independent of the gas flow rate, the increase in bubble diameters was less than the corresponding increase of orifice diameter. i.e., the ratio db/do decrease with increase in orifice diameter and beyond a certain value of orifice diameter, db/do was less than unity. At lower flow rates, the bubble evolution was driven entirely by the balance of tensile and buoyant forces. Numerical investigations of the effect of surface tension and density on bubble growth in constant volume regime were conducted which yielded capillary length as the parameter dictating relative tensile and buoyant effects. Experiments were conducted in pure ethylene glycol and propylene glycol and water glycerin solutions corresponding to the viscosity of the above liquids to nullify the viscous effects and study the effects of surface tension on bubble growth. It was observed that during the entire range of flow rates, the normalized bubble diameter in case of glycerin solutions were greater than or equal to t (open full item for complete abstract)

Committee: Raj Manglik Ph.D. (Committee Chair); Milind Jog Ph.D. (Committee Member); Sarah Watzman Ph.D. (Committee Member) Subjects: Mechanical Engineering

MS, Kent State University, 2019, College of Arts and Sciences / Department of Earth Sciences

Manganese (Mn), an essential nutrient critical for photosynthesis in plants but a toxic element in excess, impacts the fate and transport of other nutrients and toxins, forest metabolism, carbon storage, and ecosystem productivity. Given the significant role Mn can play in ecosystems, it is important to understand how soil geochemistry controls Mn uptake by vegetation. The purpose of this research was to explore how Mn uptake by plants is related to Mn supply to plants through mineral dissolution. We conducted a greenhouse pot experiment to quantify Mn uptake by plants based on controlled geochemical constraints. Specifically, we investigated whether Mn uptake was limited by the supply of Mn to soil solution or by biological controls within the plants. Greenhouse soil pots (quartz sand + peat) that were non-vegetated or vegetated with red maple saplings were supplied with either no added Mn, dissolved Mn, Mn oxides, or crushed shale containing Mn-bearing pyrite. We analyzed the chemical composition of plant tissue to quantify Mn uptake and soil leachate to quantify Mn losses. From these values, we constructed a mass balance model and calculated pseudo-first order rate constants to compare Mn mobilization between treatments. Mn uptake was higher in systems with dissolved Mn because it was not limited by mineral weathering. Mn uptake was also higher in systems supplied with fast-weathering substrates (pyrite in the shale) than slow-weathering substrates (Mn oxides). There were not significant differences in Mn leaching and total Mn loss between vegetated and non-vegetated pots in the Mn-oxide or shale treatments. We conclude that Mn uptake is controlled by dissolution rates of Mn-minerals in soil.

Committee: Elizabeth Herndon (Advisor); David Singer (Committee Member); Chris Blackwood (Committee Member) Subjects: Biogeochemistry; Environmental Geology; Environmental Science; Environmental Studies; Geobiology; Geochemistry; Geology

Master of Science in Mechanical Engineering (MSME), Wright State University, 2018, Mechanical Engineering

Environmental and safety concerns have necessitated a phase-out of lead-based alloys, which are often used in electronics solder applications. In order to properly assess suitable replacement materials, it is necessary to understand the deformation mechanisms relevant to the application. In the case of electronics solder, creep is an important mechanism that must be considered in the design of reliable devices and systems. In this study, Power-Law and Garofalo constitutive creep models were derived for two medium temperature solder alloys. The first alloy is known by the commercial name Indalloy 236 and is a quaternary alloy of lead, antimony, tin, and silver. The lead-free alternative is a binary alloy of tin and antimony known by the trade name Indalloy 264. Constant strain rate tests were conducted at temperatures from -20 to 175 Celsius using constant strain rate tensile testing in the range of e-5 s-1 to e-1 s-1. Creep constants were defined for use in materials selection and design analysis activities.

Committee: Daniel Young Ph.D. (Advisor); Raghavan Srinivasan Ph.D., P.E. (Committee Member); Joseph Slater Ph.D., P.E. (Committee Member) Subjects: Aerospace Materials; Materials Science; Mechanical Engineering; Mechanics

Doctor of Philosophy in Engineering, University of Toledo, 2009, Mechanical Engineering

Working prototypes of a Hydraulic Hybrid Vehicle (HHV) are already under testing and investigation. One of the problems reported from testing is that the noise levels emitted by the hydraulic system are not acceptable. Therefore, there is a need to perform extensive research to improve the HHV systems in terms of noise and performance. The pump is the main source of noise in HHV systems. However, the lack of space, the high pressure and the dynamics of components within the pump have prevented either direct observation or measurement of potential noise causing mechanisms within the pump structure. As a result, there are several theories as to the source of the noise from the pump units but little concrete information to further isolate and reduce the noise generation.Currently, the industry use “cut and try” methods in order to study the noise issue. This necessities the development of a theoretical tool that will enable us to avoid the costly (time and money) cut and try procedure already employed in the current efforts. This work creates a dynamic and geometric model of a bent axis pump for this purpose. Elements of the model include finding the variation of pressure, flow rate, and dynamic forces acting on the pump components and case as a function of angular rotations of both the main shaft and the yoke. The model was constructed using MathematicaTM” software and verified against test data. In turn, this study identifies and analyzes the dominant forces in both the time and frequency domains. The solution of the theoretical model using MathematicaTM is verified by a dynamic model created using ADAMS/View software. The kinematic model was able to predict the variations of the angular velocities and accelerations and the velocities and the accelerations of the center of gravity of the entire pump's parts starting from the main shaft up to the yoke. This work presents all equations necessary to solve for the piston pressure and pump flow rate as a function of main (open full item for complete abstract)

Committee: Walter Olson PhD (Advisor); Mohammad Elahinia PhD (Committee Member); Maria Coleman PhD (Committee Member); Sorin Cioc PhD (Committee Member); Efstratios Nikolaidis PhD (Committee Member) Subjects: Engineering; Fluid Dynamics; Mathematics; Mechanical Engineering; Mechanics; Technology