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 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

Doctor of Philosophy in Materials Science and Engineering, Youngstown State University, 2023, Materials Science

This work discusses the relevance of Metal Additive Manufacturing (MAM) and focuses on one method: Direct Energy Deposition (DED). Different types of DED processes are discussed, including their main parameters and issues. A general procedure to simulate DED processes is presented and founded on the finite element analysis (FEA) workflow. Based on this, two initial case studies are analyzed, which were selected from the literature and reproduced via a commercially available FEA software. Their results provided evidence of the feasibility of the software in simulating a DED process. Two experiments were carried out, called single bead and rectangular prism, for the purpose of this research. These were built with a hot wire and laser DED system, where experimental thermal data was obtained. Geometric information was obtained later via a 3D scan. Limitations of the equipment used as well as observed defects in the material deposition are discussed based on the experimental data. FEA models were developed to duplicate the experiments, which included a detailed geometry of the single bead. Two modifications to the bead geometry are presented and evaluated, where it was concluded that a semicircular bead approximation provides better results than if a rectangular one is assumed. This led to the definition of a thermal and structural equivalent model of the single bead, which was the basis for the numerical work of the rectangular prism. The results obtained for the latter show good agreement with the thermal results, although differences in the structural results are perceptible.

Committee: Kyosung Choo PhD (Advisor); Pedro Cortes PhD (Committee Member); Timothy Wagner PhD (Committee Member); Jae Joong Ryu PhD (Committee Member); Holly Martin PhD (Committee Member) Subjects: Experiments; Materials Science; Mechanical Engineering; Mechanics

Master of Science in Mechanical Engineering (MSME), Wright State University, 2022, Mechanical Engineering

Repairing airfoil blades is necessary to extend the life of turbine engines. Directed energy deposition (DED) additive manufacturing (AM) provides the ability to add material at a specific location on an existing component. In this work, AM repairs on Ti-6Al-4V airfoil blades were analyzed to determine what effect the repair will have on the blade performance in high cycle vibration fatigue testing. Targeted sections were cut out of airfoil blades near high stress locations and repaired using DED. To understand the defects that arose with this type of repair, computed tomography imaging was used to quantify the defects from the AM process. The blades were then tested until failure using vibration bending fatigue to simulate turbine engine loading conditions. Results suggest that understanding the impact of internal and surface level defects arising from the AM process is critical towards the implementation of AM repair in aerospace components under fatigue loading.

Committee: Joy Gockel Ph.D. (Advisor); Nathan Klingbeil Ph.D. (Committee Member); Onome Scott-Emuakpor Ph.D. (Committee Member) Subjects: Mechanical Engineering

Master of Science in Engineering, Youngstown State University, 2018, Department of Mechanical, Industrial and Manufacturing Engineering

Additive manufacturing (AM) is a method to build a three-dimensional part through the layering of material. One category of AM, Direct Energy Deposition (DED), is commonly used with the titanium alloy, Ti-6Al-4V, and has shown to be useful for aerospace, transportation, and biomedical applications. However, the DED process induces anisotropic material properties due to the nonuniform temperature distribution, which causes residual stresses. In addition, when handling titanium and its alloys, the processing history and post-heat treatment greatly influence the microstructure, residual stresses, and mechanical properties. Previous research has been done to investigate the residual stresses by methods such as X-ray diffraction, contour methods, and finite element simulations. However, a less established technique for determining the residual stresses is through nanoindentation. Nanoindentation is the use of instrumented indentation to determine the mechanical behavior and properties of a small volume based on the load versus depth results. By applying nanoindentation techniques to a DED Ti-6Al-4V, it was found that the nanoindentation results varied based on the cross-sectional height of the sample. The reason for this occurrence was believed to be due to the microstructure and the existence of residual stresses. The nanoindentation results were then used to quantify the residual stresses present in the DED Ti-6Al-4V part using the basic methodology of Suresh and Giannakopoulos. Similar to the nanoindentation hardness and elastic modulus results determined, the residual stresses also showed an increasing trend when increasing in height along the cross-section. More specifically, as the height along the build direction increased, the residual stresses present increased in compressive behavior. However, future work is required to verify the validity of the Suresh model and its application to DED Ti-6Al-4V. Ultimately, by understanding the material characteristics of this (open full item for complete abstract)

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