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

The field of metal additive manufacturing has experienced significant growth in recent years, and Laser Hot Wire Directed Energy Deposition (LHW-DED) has emerged as a popular technology due to its ease of use and ability to produce high-quality metal parts. In this study, we used a nonlinear transient thermo-mechanical coupled finite element model (FEM) in ANSYS APDL to conduct a detailed thermal and structural analysis of the laser hot wire DED metal additive manufacturing process. This analysis aimed to characterize the distortion caused by thermal effects and investigate the transient thermal process. In this study H13 iron chromium alloy material was deposited on an A36 low carbon steel substrate using a bidirectional laser toolpath. To record the temperature profile during printing, we employed a FLIR Infrared (IR) camera, while thermocouples mounted to the base plate measured heat transfer for validation purposes. Post-processing analysis was conducted using the CREAFORM laser 3D scan and Geomagic-X software to measure deformation from the nominal printed geometry. Overall, this study provides a significant contribution to our understanding of laser hot wire DED metal additive manufacturing, which will undoubtedly lead to further advancements in the field. This research has the potential to improve the productivity and quality of the additive manufacture of metals.

Committee: Kyosung Choo PhD (Advisor); Jae Joong Ryu PhD (Committee Member); Alexander H. Pesch PhD (Committee Member) Subjects: Aerospace Materials; Engineering; Materials Science; Mechanical Engineering

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

This is a study on optimizing the Laser Hot-wire Directed Energy Deposition (LHW-DED) process Invar 36 steel deposition onto an A36 mild steel substrate. This study aims to investigate Numerical Analysis as well as thermocouple measurements, on the transient thermal model to discuss potential solidification mechanisms. Unlike most-existing studies which focus is on single or few-layer geometries, this research presents a multi-layered model capable of predicting thermal analysis during deposition. A transient thermal model was developed to evaluate the effects of conduction, convection and radiation on the printing beads. The numerical model results were compared with the temperature data measured using thermocouples. The integration of experimental and numerical approaches enhance the accuracy of the findings, providing valuable insight into the thermal behavior of the DED process. This understanding is crucial for optimizing parameters and improving the quality of printed structures. The study highlights the significance of accurately modeling thermal interactions to advance the precision and efficiency of DED additive manufacturing. The detailed study of the LHW-DED additive manufacturing process focusing on the experimental setup, materials used, and the potential impact of the research on advancing the understanding and application of this innovative manufacturing technology. The numerical simulation with experimental data is to ensure the accuracy of the thermo-mechanical model. This will involve in measuring profiles, residual stresses, and material properties during the actual LHW-DED process.

Committee: Kyosung Choo PhD (Advisor); Jae Joong Ryu PhD (Committee Member); Alexander Pesch PhD (Committee Member) Subjects: Materials Science; Mechanical Engineering

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

A longitudinal study in corrosion was performed on tensile-elongation dog-bones, created using 3D-printed stainless steel. The effects of exposure to an acidic environment were investigated regarding mass-loss, tensile and yield strength, modulus of elasticity, profilometry of pits and defects, and microscopy of fracture-sites. The SS316L specimens were manufactured using different print-directions, specifically overlapping unidirectional or rotated bidirectional for each layer by an additive manufacturing unit, the Mazak VC-500/5X AM HWD. The novel aspect of this research is focusing on the differences that the path the hot-wire, direct energy deposition, print-head has on its corrosion characteristics, as opposed to only focusing on the printing-parameters. The goal was to determine what printing-directions and methods were best for resisting corrosion. The research outlines the process of preparing samples for controlled weight-loss in HCl as well as the methods used to measure the mechanical properties. This allows for the results to be repeated if desired. Upon thoroughly reviewing the data and drawing connections where applicable, it was determined within the test samples that unidirectional print-directions yielded better mass-loss and mechanical attributes than bidirectional printing. It was found that some print directions, namely 90°, which is perpendicular to the printing door, performed notably better than other directions such as 0° or 45°.

Committee: Holly Martin PhD (Advisor); Pedro Cortes PhD (Committee Member); Bharat Yelamanchi PhD (Committee Member) Subjects: Chemical Engineering; Chemistry; Engineering; Experiments; Materials Science

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

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

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

Master of Science, The Ohio State University, 2023, Environment and Natural Resources

The American elm (Ulmus americana) was once found lining the streets of many cities. Now, with the continued threat of Dutch elm disease (Ophiostoma ulmi and O. novo-ulmi), large American elms are uncommon. Efforts by researchers have led to the development of Dutch elm disease-tolerant American elm selections. Yet we have little understanding of how these selections may react to a range of environments when used in restoration. Our goal is to better understand how DED-tolerant elms differ in phenology across locations and genotypes to develop predictions for how they may respond to restoration and future climate change. In common gardens in central Ohio and northern New England, we tracked the progression, time to initiation and time to completion of budbreak and leaf-out, in DED-tolerant elms. We assessed individuals across five genotypes – Princeton, R18-2, Del-2, New Harmony, and Valley Forge – which have been cultivated to produce DED-tolerant lines. Phenological data, i.e., dates at which a tree's buds reached a given stage, collected in central Ohio over two field seasons (spring 2022 and spring 2023) and in New England over one field season (spring 2023) were used to determine the relationship between time and phenology, and the effects of location, year, genotype, and genotype interactions. Data on bird presence and use of elm trees in sites in central Ohio during spring 2023 were used to better understand the potential role of restored elms within the landscape. We found that year and location effects were significant at more stages than genotype or interaction effects – colder locations and the year with later spring warming tended to result in elms reaching key phenological stages later than warmer locations and the year with earlier spring warming. This indicates that environmental factors may have a stronger influence on spring phenology in American elms than genotype. We also found that bird presence had a strong positive correl (open full item for complete abstract)

Committee: Stephen Matthews (Advisor); Jo Peacock (Committee Member); Matt Davies (Committee Member); Kristin Mercer (Advisor) Subjects: Forestry; Natural Resource Management

Master of Science in Engineering, University of Akron, 2020, Mechanical Engineering

Ti-6Al-4V is extremely used and still a promising in aerospace and turbine engines, where fracture toughness and fatigue crack growth resistance are considered as primary important mechanical properties. As repair of damaged turbine blade are challenging with conventional techniques based on criticality of structural parts; directed energy deposition additive manufacturing (DED AM) is in use to repair the damaged parts without total replacement. This has given an interest to have clear ideas in studying the properties of the AM materials in the growth and perpendicular to the growth direction. In this study the use of compact specimens to determine the anisotropy of fracture toughness and fatigue crack growth of DED AM Ti-6Al-4V were investigated. The specimens were originally part of an additive manufacture (AM) repaired study where AM material was added to an already existing commercial wrought Ti-6Al-4V bar. In order to assess the AM material and compare it with the wrought material, a smaller geometry specimen was required. Mode 1 fracture toughness and fatigue crack growth tests were performed under loading conditions to compare the fracture toughness and fatigue crack growth properties and to study the effect of crack geometry. The modes of fractures associated with microstructures were analyzed based on observation of the fracture surfaces. To have a clear insight on causes of failure mechanisms, the mirror-like polished fractured surfaces were subsequently subjected to optical and scanning electron microscopical examinations and the influences of the microstructures on mechanical properties were studied and characterized. The full-field displacements were measured and recorded using 5M DIC equipment. The mechanical testing was supported using electrical resistance (ER) as non-destructive technique to monitor and sensitively capture the formation and growth of cracks in chosen specimens and the data obtained was appropriately analyzed to measure the (open full item for complete abstract)

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

Master of Science in Botany, Miami University, 2019, Biology

The secondary-growth hardwood forest of Rush Run Wildlife Area (RRWA), Preble County, Ohio was studied 54 years after an initial study was conducted in 1964. Although Dutch elm disease (DED) was likely present in the area by the late 1930s to early 1940s, American elm (Ulmus americana L.) was recorded as one of the dominant canopy species (avg. relative density = 15.1%) and subcanopy species (9.0%) in 1964. Seedlings of American elm were also noted to be abundant across RRWA. Of the 17 plots used in 1964, 10 were chosen based on the previously recorded high relative density of American elm and resurveyed. By 2018, American elm was absent from the canopy, subcanopy, and seedling layers. A secondary analysis of measurements taken in 2018 that included dead standing Fraxinus spp. showed that the current loss of ash was extensive but non-impactful upon other species. Findings oppose the previous predictions that American elm can persist indefinitely in forest stands following introduction of DED but restricted to subcanopy and smaller stature. It is possible that previous studies have not allowed adequate time after introduction of DED to accurately assess the effects on American elm.

Committee: Michael Vincent PhD (Advisor); Richard Moore PhD (Committee Member); David Gorchov PhD (Committee Member) Subjects: Botany; Ecology; Plant Sciences