Master of Science (M.S.), University of Dayton, 2018, Civil Engineering

This research investigates the effect of nano-SiO2 on porosity and strength. In both compressive strength and porosity tests, nano-SiO2 is varied from 0 to 3% (0%, 0.5%, 1%, 2%, 3%) with the fixed percentage of silica fume at 0.4%. In addition to these tests, a base test was performed that did not include SF or nano-SiO2. However, for the flexural test, only the 0% and 1% of nano-SiO2 are tested (1% is the optimal percentage for the porosity test). Also, one specimen, which does not include either SF or nano-SiO2, is tested. Results show compressive strength increases with the increase of nano-SiO2, but this increase stops after reaching 2%. Porosity decreases when the nano-SiO2 percent increases. However, such a decrease stops after reaching 1%. An increase of 0.5% of nano-SiO2 contributes to reducing the porosity by 40%, compared to a specimen that has 4% of silica fume and 0% of nano-SiO2. However, an increase of 1% of nano-SiO2 contributes to reducing the porosity by only 2.4% because nano-SiO2 particles are more beneficial on the surface layer. Consequently, most of the nano-SiO2 particles that are in the core layers are redundant because the surface layer decreases the porosity sufficiently. The flexural strength seems to increase with the increasing percentage of nano-SiO2, compared to 4% of silica fume and 0% of the nano-SiO2 specimen.

Committee: Joseph Saliba (Committee Chair); Riad Alakkas (Committee Member); Ben Weghe (Committee Member) Subjects: Civil Engineering; Nanotechnology

Master of Science (MS), Wright State University, 2007, Earth and Environmental Sciences

Porosity and permeability are parameters that affect the flow of ground water in the subsurface and have significant implications on the modeling of fate and transport of contaminants. However, little has been done to quantitatively examine the effect on porosity and permeability of packing in bimodal mixtures of natural sediment. This study compares measurements of porosity and permeability on model bimodal sediment mixtures with predictions from petrophysical models. The main goal is to evaluate how well these petrophysical models predict porosity and permeability in bimodal mixtures of natural sediment. The effect of the volume fraction of fines on porosity and permeability within bimodal sediment mixtures using natural grain size components will also be examined. First, I took measurements on the mixtures to determine porosity values. Then I compared these values to those predicted by the expanded fractional packing model for porosity. The expanded fractional packing model for porosity represents mixtures in which finer grains approach the size of the voids among the pre-mixed coarser grains. Next, I utilized a grain size statistical method to derive estimates for permeability, using the measured porosity values. I then compared these estimates to measured permeability values. I took permeability measurements on the mixtures using air- and water-based methods. Finally, I made conclusions about the petrophysical models for porosity and permeability to determine whether or not they were applicable to natural sediment. These conclusions will help to improve the confidence in estimating the parameters of porosity and permeability.

Committee: David Dominic (Advisor) Subjects: Geology; Hydrology

Bachelor of Science (BS), Ohio University, 2017, Biological Sciences

Osteoporosis is a disease characterized by diminished bone strength, resulting in an increased risk for fracture with minimal trauma. Though osteoporotic fractures present severe consequences for patients and health communities alike, there remains to be an accurate diagnosis for this disease. There are many characteristics that influence bone strength, ranging from mechanical, microstructural, to geometrical in nature. This project specifically aimed to assess cortical porosity, diameter, and bending stiffness as predictors of bending strength in the human radius. Data was collected from thirty cadaveric human radii from men and women between the ages of 17-99 years. Bending strength and bending stiffness were measured by the gold standard three-point bending method, quasi-static mechanical testing (QMT). Interosseous diameter was measured from both higher resolution µCT and lower resolution CT scans. Finally, cortical porosity was measured from µCT scans in the NIH image-processing software ImageJ. These measurements were guided by 3D Avizo models. Simple linear regression analyses revealed that bending stiffness predicted bending strength with the least amount of uncertainty (SEE=3.2 Nm). Cortical porosity demonstrated the weakest relationship with bending strength (SEE=12.0 Nm). Predictions of bending strength by µCT diameter were not different from those made by CT diameter (p=0.37). In comparisons of cortical porosity in the radius and ulna as imaged from the same arms, porosity at the 55%L of the ulna was the only unbiased predictor of radius porosity adjacent to the QMT fracture site (p=0.12). Thus, at the midshaft, cortical porosity of the ulna and radius appear to be indistinguishable.

Committee: Anne B Loucks PhD (Advisor) Subjects: Anatomy and Physiology; Biology; Cellular Biology; Endocrinology; Kinesiology; Medical Imaging; Molecular Biology; Morphology; Physiology

Bachelor of Science in Petroleum Engineering, Marietta College, 2013, Petroleum Engineering and Geology

It has been hypothesized that utilizing current well logging practices, with Dual Water Theory, it is possible to identify all minerals within rock formations. The purpose of this study was to develop software that supports this hypothesis. It also was created to demonstrate a hypothesized plotting correlation discovered by Professor Ben Ebenhack. The results show promise in supporting this hypothesis correct, and recommendations for future adjustments to the software are given.

Committee: Ben Ebenhack (Advisor); Robert Van Camp (Committee Member); David Brown (Committee Member) Subjects: Petroleum Engineering; Petroleum Geology

Doctor of Philosophy, University of Akron, 2024, Mechanical Engineering

For CMCs with an electrically conductive matrix, direct current potential drop techniques have the potential to detect composite state such as conductive constituent content (e.g., Si in melt infiltrated composites) or local defects such as delamination or porosity. Melt-infiltrated SiC based composites are an ideal candidate material for such to verify this since the Si content of the matrix is the primary current carrier in the system. In our study, we aimed to evaluate the effectiveness of Electrical Re-sistance (ER) as a NDE method for different 2D woven SiC-based Melt-infiltrated composites, each exhibiting varying degrees and types of processing defects. We con-ducted four types of ER measurements: a. Bulk Resistivity b. Through-thickness c. Axial d. Surface, along the length of the dogbone specimens in the gauge section and on a large plate. Microstructural analysis was performed to correlate observations with microstructure. The bulk resistivity of the specimens in our study exhibited a linear correlation with the infiltrated Si content of the matrix even with different percentage and type of porosities present, allowing us to comment on Si-content of the speci-mens. The Through-thickness set-up incorporates current leads to supply current in a through-thickness manner and determine the nature of current spreading (voltage drop) some distance   away from the current source. The absolute values of the measured through thickness potential represent Si-content, but it is unresponsive for processing defects. The axial set-up is more conventional and can generate local axial current flow. In some cases, such flow of current is affected by and able to locate the local and distinct type porosi-ty. Resistance was sensitive for regions of poor Si-infiltration i.e., “dry-slurry” type defects as well as for isolated larger rounded porosity. It was very sensitive to local surface porosity but not as sensitive for cases where porosity was homogenously pre-sent throug (open full item for complete abstract)

Committee: Dr. Gregory N Morscher (Advisor); Dr. Wiesław K Binienda (Committee Member); Dr. Siamak Farhad (Committee Member); Dr. Jun Ye (Committee Member); Dr. Manigandan Kannan (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2024, Materials Science and Engineering

Aluminum is increasingly favored in the automotive sector for its favorable mechanical properties and good strength-to-weight ratio. Laser welding finds utility in electric vehicle battery assemblies, while high pressure die castings (HPDC) are used in vehicle body construction. Nonetheless, defects pose a risk to the mechanical robustness of aluminum welds and cast parts. These defects include hydrogen porosity, entrapped air, and externally solidified crystals (ESCs). In this study, defects in die-cast and welded aluminum were investigated to understand their formation mechanisms and to explore methods for their prevention. Laser welding of aluminum and copper is commonly used in the battery assemblies of electric vehicles. However, aluminum is prone to forming hydrogen porosity when welded. The investigation of hydrogen porosity in aluminum welds involved the utilization of scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), microcomputed tomography (\textmu-CT), and LECO\textsuperscript{\textregistered} analysis. It was observed that the oxide layer on anodized aluminum served as heterogeneous nucleation sites for hydrogen porosity. Anodized aluminum can contribute to increased hydrogen content in the liquid phase. As liquid aluminum solidifies, hydrogen is forced into the melt, leading to a state of supersaturation in the liquid. This supersaturation prompts the nucleation and growth of hydrogen porosity. Additionally, a cellular automaton (CA) model was expanded to predict hydrogen porosity under different hydrogen concentrations, laser speeds, and powers. To mitigate hydrogen porosity, it is necessary to either improve the cleaning process of the anodized aluminum or utilize an alternative corrosion-resistant material. Die-cast aluminum is frequently employed to reduce vehicle weight. However, the turbulent flow inherent in the die casting process can easily entrap air, leading to gas porosity. The impact of vacuum on entrapped a (open full item for complete abstract)

Committee: Alan Luo (Advisor); Ahmet Selamet (Committee Member); Xun Liu (Committee Member); Glenn Daehn (Committee Member) Subjects: Materials Science

Doctor of Philosophy (Ph.D.), University of Dayton, 2023, Materials Engineering

Additive manufacturing (AM) has evolved as a convenient technology for rapid fabrication of prototype tooling and complex geometry components. Among all AM techniques, FFF is the most widely used for making polymeric structures. However, the process consistency and control of properties in the manufactured articles remains a challenging issue. The current study aims to investigate physical changes in polylactic acid (PLA) during 3D printing. The correlations between porosity, crystallinity and mechanical properties of the printed parts were studied. Moreover, the effects of bed-plate temperature were investigated. Experimental results confirmed the anisotropy of printed objects due to the occurrence of orientation phenomena during filament deposition and the formation both of ordered and disordered crystalline structures (α and δ, respectively). A post-3D printing heat treatment cycle was demonstrated as an effective method to improve mechanical properties by optimizing the crystallinity (transforming the α form into the δ form) and overcoming the anisotropy of the 3D printed object. The second approach to enhance the physical and chemical properties of neat PLA is by using nano-additives such as carbon nanotubes (CNTs) and carbon black (CB). 4 As the concentration of carbon nanotubes increased the mechanical and electrical properties were improved even with low volume ratio of CNTs. In molten polymer and under shear force CNTs tended to align parallel to the shear direction leading to significant increase in electrical properties in the direction of alignment. Also, a change in the enthalpy of cold crystallization was observed. The enthalpy of cold crystallization of PLA/CNT samples was lower than pure PLA because of a change in the type of crystallites formed during cold crystallization. The presence of carbon nanotubes reduced the crystallization domain leading to the formation of unstable crystalline phase δ, which was remarkably disordered compared to that o (open full item for complete abstract)

Committee: Khalid Lafdi (Committee Chair); Youssef Raffoul (Committee Member); Donald Klosterman (Committee Member); Li Cao (Committee Member) Subjects: Materials Science

Master of Science in Polymer Engineering, University of Akron, 2023, Polymer Science

Porous membranes exist in a wide variety of biological systems in nature as they are a simple method for the system to exchange gases with the outside world. However, pores offer little to no control over this exchange and the exchange rate of these gases is determined by the physics of diffusion. This becomes significant for systems such as plants and eggs, where the systems want to take in as much CO2 or oxygen as it needs while losing as little water as possible. It has been suggested that these systems use unique pore geometry to overcome this fixed exchange rate, but there has been no definitive conclusion as to the physical mechanism that would achieve this. By measuring the flux through a variety of geometrically diverse synthetic pore sets we aim to better understand the influence pore geometry has on diffusion.

Committee: Hunter King (Advisor); Ali Dhinojwala (Committee Member) Subjects: Biophysics

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

Self-healing concrete is an innovative and challenging solution in the construction industry to self-repair cracks that appears on the concrete surface. Many researchers are actively working to find economical and effective methods to achieve self-healing that employ biological and chemical approaches. The main advantages of using self-healing concrete, which is commonly implemented using bacteria or various other substances, are a reduction in the repair costs for structures built using concrete and an increase in the reliability and durability of the structures. It is also a better alternative than traditional practices for repairing concrete cracks because it helps the concrete to retain its original appearance. Although self-healing is an excellent approach, it has not yet been commercialized because of limited experimental studies, a lack of systematic evaluation procedures, or unfeasible production costs. The work described in this dissertation is focused on the introduction of a microbial-based self-healing concrete that uses fungi, development of a suitable evaluation procedure for self-healing concrete and investigating the influence of the fungus and its nutrients on the cementitious material. It is assumed that a fungus-based self-healing concrete can be an economical method if the concrete properties remain intact and the nutrients allow the fungus to survive inside the concrete. Possible nutrients for the fungi are selected to verify this possibility, and the influence of the nutrients and fungi on the mortar and concrete is studied. In addition, a suitable analytical procedure has been proposed that can help to estimate the effectiveness of using self-healing concrete with respect to porosity and permeability.

Committee: Anil Patnaik (Advisor); Ping Yi (Committee Member); David Roke (Committee Member); Lu-Kwang Ju (Committee Member); Jun Ye (Committee Member) Subjects: Civil Engineering; Engineering; Materials Science

Master of Science in Materials Science and Engineering (MSMSE), Wright State University, 2022, Materials Science and Engineering

Additive Manufacturing (AM), particularly laser powder bed fusion, is being studied for use in critical component applications. Tensile and fatigue testing shows differences when built using different laser powers. However, when fabricated in an as-printed geometry, the gauge sections of the two specimens are different and experience different thermal behavior. This work explores microhardness, microstructure size, Niobium segregation, and porosity from samples made with varying laser power and different build geometry sizes representative of the gauge sections in the tensile and fatigue bars. Results show that microhardness varies spatially across the sample. Smaller diameter metallographic coupons (fatigue diameter) have a coarser microstructure and lower microhardness than the larger diameter (tensile diameter) when built using the same parameters. Therefore, the fatigue and tensile properties are not comparing the same material structure. Understanding the effect of build geometry on microstructure provides insight towards consistency in AM mechanical properties testing strategies.

Committee: Henry D. Young Ph.D. (Committee Co-Chair); Joy Gockel Ph.D. (Committee Co-Chair); Onome Scott-Emuakpor Ph.D. (Committee Member) Subjects: Engineering; Materials Science

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

Laser Powder Bed Fusion (L-PBF) is a branch of metal additive manufacturing technologies which has become increasingly more popular due to the geometric freedoms and strategic design methods which it allows. L-PBF produces metallic components to near net shape within a single process step while simultaneously allowing for the creation of complex geometries and internal structures which are not readily produced by other manufacturing techniques. Not without issues, L-PBF produces materials with preferential directions of growth in the underlying material microstructure as well as undesirable phase content in many cases. While techniques exist to change microstructure of L-PBF materials, many rely on post-processing or in situ control over the flow of heat. This thesis documents the development and analysis of a novel technique separate from previous methods which allows for in situ modification of grain structure produced in LPBF without the need of complex modification of the machine. Ultrasonic vibrations are introduced to the build process as an added parameter, hypothesizing that in situ ultrasonic cavitation will reduce grain size and modify the formation of secondary phases in a way that is beneficial to the as-manufactured material properties.

Committee: Brian Wisner (Advisor) Subjects: Mechanical Engineering

Doctor of Philosophy, University of Akron, 2022, Integrated Bioscience

Opioids have become one of the most misused classes of prescribed medication. Synthetic opioids (e.g., fentanyl) have been responsible for most opioid overdose deaths since 2017. As this epidemic shows no signs of slowing, it is imperative to study the effects of opioids on various aspects of health including bone maintenance. Endogenous opioids (e.g., met-enkephalin) are involved in osteogenesis and bone remodeling. Exogenous opioids can interfere with bone maintenance directly through binding to osteoblasts, limiting bone formation, or indirectly through a cascade of effects limiting sex hormone production. To understand how opioids affect bone microarchitectural and biomechanical properties we first examine bone microstructure throughout the human lifespan to see natural changes occurring without the effects of opioids. Using both Synchrotron Radiation micro-Computed Tomography and confocal laser microscopy, we found bone and lacunar volume fractions to decrease with advancing age while pore diameter increased in the anterior midshaft femur. After finding how bone changes with age under normal circumstances, we sought to examine how prolonged opioid administration affected trabecular microstructure in a model organism (rabbit). We used μCT to examine the proximal tibia by anatomical quadrant (e.g., anterior, posterior). We found that morphine animals had greater bone volume fraction and less trabecular separation than controls. Fentanyl animals had significantly thicker trabeculae and increased trabecular spacing than controls. Detected differences by anatomical region followed the same overall pattern, suggesting biomechanical or anatomical variation rather than due to opioids. We finally examined overall bone strength in a non-weight bearing bone (rib) of the rabbit using uniaxial compression testing to determine how opioids affect overall mechanical competency. We found no difference in mechanical variables between opioid and control groups. Only rib span leng (open full item for complete abstract)

Committee: Brian Bagatto (Advisor); Janna Andronowski (Committee Co-Chair); Henry Astley (Committee Member); David Cooper (Committee Member); Christine Dengler-Crish (Committee Member); Nita Sahai (Committee Member) Subjects: Biology; Biomechanics; Histology; Pharmaceuticals; Physiology

Master of Science in Materials Science and Engineering (MSMSE), Wright State University, 2022, Materials Science and Engineering

This work investigates processing parameters for laser powder bed fusion (LPBF) additive manufacturing (AM) to produce bismuth telluride coupons. AM provides the ability to fabricate complex geometries, reduce material waste, and increase design flexibility. The processing parameters for LPBF were varied in single bead experiments guided by analytical modeling to identify conditions that result in uniform beads. Coupons were built using these processing parameters and the cross-sections characterized using optical microscopy (OM), scanning electron microscopy (SEM), and energy dispersive x-ray spectroscopy (EDS). Porosity analysis using OM concluded most coupons had porosity levels less than 10% by area. SEM and EDS analysis revealed there were slight composition and microstructure variations throughout the cross-sections depending on the processing conditions. These results show that LPBF is a viable process for producing bismuth telluride coupons with low porosity. Investigations of the microstructure and composition of the coupons indicate further research opportunities.

Committee: Joy Gockel Ph.D. (Advisor); Henry D. Young Ph.D. (Committee Member); Raghavan Srinivasan Ph.D., P.E. (Committee Member) Subjects: Engineering; Mechanical Engineering

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

Master of Science (MS), Wright State University, 2021, Earth and Environmental Sciences

The Theis Environmental Monitoring and Modeling Site is a field research facility, located on the Great Miami River in southwest Ohio, dedicated to the study of hyporheic zone processes. The site is underlain by an aquifer on the order of 21 meters thick, comprised of fluvial deposits. The permeability of the aquifer sediments was quantified both from one large scale hydraulic test (~100 m radial distance) and from grain-size analysis of 119 small-scale core samples (~20 cm length each). The permeability determined from the large-scale hydraulic test is 98.9 Darcies. The test also gave a value for specific yield of 0.25. The geometric mean of the small-scale measurements is 88.3 Darcies, close to the value of the large-scale measurement, and within the central tendency of the distribution of previously published measurements. The aquifer contains an inferred hierarchy of sedimentary architecture, with compound bar deposits comprising unit bar deposits, and unit bar deposits comprising stratasets with different grain-size facies, including sand, gravelly sand, sandy gravel, and gravel. The stratasets are less than a meter thick and less than 10 meters in length. Intervals of sand facies make up 18.5% of the aquifer, have a mean thickness of 0.75 m (standard deviation (σ) of 0.37 m), a mean permeability of 86.8 Darcies (σ of 47.8 Darcies), and a mean porosity of 36% (σ of 4%). Intervals of gravelly sand facies make up 25.2% of the aquifer, have a mean thickness of 0.96 m (σ of 0.46 m), and a mean permeability of 73 Darcies (σ of 49.9 Darcies), and a mean porosity of 28% (σ of 3%). Intervals of sandy gravel facies make up 36.1% of the aquifer, have a mean thickness of 1.00 m (σ of 0.79 m), and a mean permeability of 84.9 Darcies (σ of 49.7 Darcies), and a mean porosity of 25% (σ of 3%). Intervals of gravel facies make up 20.2% of the aquifer, have a mean thickness of 1.10 m (σ of 0.74 m), and a mean permeability of 670 Darcies (σ of 1170 Darcies), and a me (open full item for complete abstract)

Committee: Robert W. Ritzi Jr., Ph.D. (Committee Chair); David A. Schmidt Ph.D. (Committee Member); David F. Dominic Ph.D. (Committee Member) Subjects: Geological; Geology; Hydrologic Sciences; Hydrology

Doctor of Philosophy, The Ohio State University, 2022, Materials Science and Engineering

Electrospinning is an electrohydrodynamic process generating polymeric micro or nanofibers having immense technological benefits in biomedical, energy, and filtration applications. However, the microstructural heterogeneity inherent to electrospun materials has led to unreliable performance, fundamentally limiting the potential of this technology. While this heterogeneity is readily revealed by point-to-point comparisons (e.g., electron microscopy), full quantification remains challenging due to the extremely limited field-of-view associated with these techniques. To address this, we developed a novel technique that can characterize internal porosity gradients in thin films that reflect the large-scale microstructural heterogeneity of electrospun deposits. Accurate measurements of both as-spun depositions and the same depositions post-densification, are obtained via contact-free laser metrology. A formula was developed to enable ‘mapping' of the spatial porosity distribution by comparing both dimensions and quantifying the vertical shrinkage. The automated prototype developed generates porosity ‘maps' – each consisting of ~14,000 datapoints at a spatial resolution of ~1 mm – within a few hours, an achievement > 1,000 times faster than traditional methods such as porosimetry. Our technique also enables in situ characterization thus minimizing the risk of sample distortion or other artifacts. In addition, the technique is believed to be compatible with any other open-porous materials that can be densified. Utilizing this innovation, an extensive investigation was conducted to understand the porosity gradients found within tubular electrospun polycaprolactone (PCL), a frequently studied polymer thanks to its specific combination of biocompatibility and biodegradability. Variations in porosity values are found in many examples of electrospun PCL and can range from ~0 to 88% within the same deposition in extreme cases. These variations also exhibit signific (open full item for complete abstract)

Committee: John Lannutti (Advisor); Jinghua Li (Committee Member); Heather Powell (Committee Member); Pelagia-Iren Gouma (Committee Member) Subjects: Engineering; Materials Science; Mechanical Engineering; Mechanics; Nanoscience; Nanotechnology; Polymers

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

Additive Manufacturing (AM) is a rapidly developing field that offers new possibilities for manufacturing with materials that are difficult to process with traditional manufacturing methods. This report will examine the application of selective laser melting in making magnetic cores out of Hiperco 50. The iron-cobalt family of alloys is known to offer the best magnetic properties of all soft magnetic materials but is extremely brittle. Additive manufacturing offers the opportunity to make high quality magnetic cores in unique geometries that traditional manufacturing is unable to replicate. To test the viability of this process three types of test specimens were built out of Hiperco 50 powder to examine key material properties. First 1 cm3 cube specimens were built to measure the density of the final parts, and they were also used to examine the porosity and microstructure. The second type of specimens were tensile bars, built in both vertical and horizontal orientations with respect to the build plate, to examine the mechanical properties of the final parts as well as the impact of build orientation. The final test specimens were magnetic toroids, comprised of cores to be wound with copper magnet wire and tested for magnetic permeability and remanence. Half of these specimens were also subjected to a final magnetic heat treatment cycle, which was the same as the cycle used for traditionally manufactured Hiperco 50 components, in order to determine the change in performance. These AM fabricated specimens showed a 1-5% decrease in density from traditionally manufactured Hiperco 50 parts, with the build parameters being the largest deciding factor of final density and porosity. These parts also had a poorly defined grain structure until subjected to a magnetic heat treatment. After undergoing the recommended heat-treatment, niobium precipitates were observed along the newly defined grain boundaries. However, there was a severe drop in mechanical performance, (open full item for complete abstract)

Committee: Donald Klosterman (Committee Chair); Zafer Turgut (Committee Member); Li Cao (Committee Member) Subjects: Electromagnetics; Electromagnetism; Materials Science

Master of Science, The Ohio State University, 2021, Welding Engineering

In aluminum welding, hydrogen contamination is the main cause of the welding defect, porosity. Porosity in welds can adversely affect the mechanical properties such as tensile strength, fatigue life and ductility. There have been a variety of solutions to help reduce porosity in aluminum welds including finding the source of hydrogen. However, in some cases the amount of hydrogen may be drastically reduced but impossible to completely eliminate. Another approach to this issue is to understand where a pore originates and how it moves and grows within the weld pool. This information may lead to a more innovative method for pore elimination during gas tungsten arc (GTA) welding of aluminum. In-situ aluminum weld experiments were set-up to observe the porosity formation in aluminum welding. Aluminum alloys 1100, 4047, and 6061 were autogenously gas tungsten arc welded in a chamber while real-time digital radiography was performed. Hydrogen was added in parts-per-million through an argon-hydrogen shielding gas. The shielding gas hydrogen was varied between 0 and 1000 ppm of hydrogen and three travel speeds were tested: 1.69 mm/s, 2.54 mm/s and 3.39 mm/s. The smallest pore measured was roughly 90μm, demonstrating this method of insitu observation to be a useful way to monitor macro-porosity in aluminum welds. Micro-pores could be seen near the surface of weld pool but it was difficult to see their shape or movement. The amount of hydrogen added through the shielding gas played an important role in macro-pore growth and well as travel speed. Pore growth rate increased with increase in hydrogen saturation and slower travel speed. In Alloy 1100 macro-pores originated at the bottom of the weld pool, near the trailing portion of the weld pool in an elliptical shape. Macro-pores in Alloy 6061 originated at the leading edge of the weld pool, near the surface. Once the macro-pores reached a favorable size, they were then swept back to the trailing edge of the weld po (open full item for complete abstract)

Committee: Carolin Fink PhD (Advisor); Boian Alexandrov PhD (Committee Member); Carl Cross PhD (Advisor) Subjects: Materials Science

Master of Science in Mechanical Engineering (MSME), Wright State University, 2020, Mechanical Engineering

The presence of defects within laser powder bed fusion (LPBF) parts can lead to reduced mechanical properties and life of components. Because of this, the ability to detect these defects within the parts is critical before the part is subject to its intended loading. Normally the parts are subjected to a quality analysis once they are completed however, this process is typically expensive and time consuming. A solution for these problems is to sense the creation of defects and pores in the parts in-situ, while the part is being fabricated. One proposed method of in-situ monitoring is visible spectroscopy to identify defects based on the light intensities during prints. In this work, in-situ spectroscopy intensities and ex-situ computed tomography defect data are compared for different processing parameters and two LPBF builds to determine correlation. Results show that changes in the signals from the spectroscopy occur for different conditions of processing parameters and geometries.

Committee: Joy Gockel Ph.D. (Advisor); Nathan Klingbeil Ph.D. (Committee Member); John Middendorf Ph.D. (Committee Member) Subjects: Materials Science; Mechanical Engineering

Doctor of Philosophy (PhD), Wright State University, 2020, Engineering PhD

In many structural applications void-like defects cause significant performance debits which call for component redesign or post-processing to account for or remove the defects. For laser powder bed fusion (LPBF) processes, it has been shown that many of these features and their size and shape characteristics are controllable through LPBF process parameter manipulation. For design efforts, however, it is necessary to understand the direct influences of processing on the formation of porosity and the role that individual pores and porosity distributions have on the properties and performance of AM components. Additionally, design criteria must be established to facilitate implementation of AM components into structurally critical applications. To this end, the investigations that have been performed here relate the AM material processing of alloy 718 to the pore structure, crack growth properties and fatigue performance. This dissertation first explores the influence of four key process parameters and scan strategies on the formation and characteristics of porosity distributions in AM material. Then, based on the porosity distributions observed via non-destructive inspection techniques, a crack-growth based life prediction method was developed to accurately predict fatigue lives of AM components. Additionally, fatigue limit models were modified based on experimental data to explore the interactions of defect size and applied stress with respect to both finite and "infinite" fatigue life which enables defect tolerant design for components manufactured via AM. Finally, a novel compliance-based method for crack initiation detection was developed and used to assess some of the assumptions made in the prior investigations. The connections made through the work presented herein link AM processing to potential design requirements which will facilitate faster, safer design efforts for implementation of AM components into structurally critical applications.

Committee: Joy E. Gockel Ph.D. (Advisor); Nathan W. Klingbeil Ph.D. (Committee Member); Ahsan Mian Ph.D. (Committee Member); Onome Scott-Emuakpor Ph.D. (Committee Member); Anthony Rollett Ph.D. (Committee Member) Subjects: Materials Science; Mechanical Engineering; Mechanics; Metallurgy