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

With more efficient computational capabilities, the use of topology optimization (TO) is becoming more common for many different types of structural design problems. Rapid prototyping and testing is often used to further validate optimized designs, but depending on a design's complexity, the structural behavior of physical models can vary significantly compared to that of their computational counterparts. For graph-based topologies such differences are caused, in part, by a need to realize finite-thickness structures from the infinitely thin geometries described by graph theory. Other differences are caused by limitations on manufacturing processes such as the need to fabricate large models from smaller components. While additive manufacturing (AM) can be more conducive for fabrication of complex topologies, its limitations are generally less understood than those for traditional subtractive manufacturing processes. Understanding and incorporating limitations on AM into a TO process in the form of added constraints would allow the algorithm to produce not only optimal designs, but also those that are feasible for AM. In this work, two specific AM constraints are characterized for Lindenmayer system (L-system) graph-based topologies of a multi-material, diamond-shaped, morphing airfoil in supersonic flow. One constraint is related to the feasible generation of thick structural members from the infinitely thin beams of graph-based topologies. To characterize the effects of geometric overlap, structural behavior of finite element models made of lower-fidelity beam elements is compared to that of finite element models made of higher-fidelity volume elements. Results indicate that at intersections where 10% or more of a member's length is overlapped, there will be significant variations in stress and effective torsional stiffness when thin members are converted to thick members. The second AM constraint characterized in this work is related to partitioning of large mo (open full item for complete abstract)

Committee: Markus Rumpfkeil (Committee Chair); Richard Beblo (Committee Member); Alexander Pankonien (Committee Member); Raymond Kolonay (Committee Member) Subjects: Aerospace Engineering; Engineering; Mechanical Engineering

Master of Science in Mechanical Engineering, Cleveland State University, 2024, Washkewicz College of Engineering

Additively manufactured blocks of Stainless Steel 316L (SS316L) have been made using three different methods and forged for comparison of material properties before and after forging. The first method used for creating the blocks was Binder-Jetting (BJ), a low-heat powder bed metal additive technique that uses glue to hold the powder together before sintering. The second method was Selective Laser Melting (SLM), a powder bed metal additive technique that utilizes a laser to melt the metal powder each layer achieving high density parts out of the printer. The final method used to create the blocks was Wire Arc Additive Manufacturing (WAAM), a form of Directed Energy Deposition (DED) that utilizes an electrified rod of filler material to create an arc and melt the filler material to a substrate, building upon itself. BJ provides complex geometry and versatility. With the low-heat printing application, this method can be used for more than just metals and can be used for combinations of powdered materials. This also allows for various post-processing procedure can be made depending on desired output and material choice. SLM provides high density parts with complex geometry directly out of the printer with minimal post processing, allowing for easier industrial use. WAAM provides parts with low-moderate geometry complexity. However, this process allows for larger parts and a faster rate of printing than SLM and BJ. After printing, and any necessary post-processing, the blocks were forged in open-die forging. The BinderJet parts resulted in low density, only coming around 62% density, and thus had v additional mass loss during the forging process and provided the worst results. Both SLM and WAAM had densities around 99% and provided beneficial results when combined with forging, showing grain reduction and grain flow characteristics. With a 25.93% increase in Ultimate Tensile Strength (UTS) for SLM and 21.66% increase in UTS for WAAM; SLM performed (open full item for complete abstract)

Committee: Tushar Borkar (Advisor); David Schwam (Committee Member); Liqun Ning (Committee Member) Subjects: Materials Science; Mechanical Engineering

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

Hybrid Additive Manufacturing (Hybrid AM) is a method of additively building and machining a three-dimensional part through layering of material and periodically machining to net-shape or finished shape. This research is designed to explore the relationship of the printing parameters of Invar 36 and its mechanical behavior through mechanical testing, microstructure and chemical composition characterization. The additive builds were made using the same process parameters and built in two orientations (XY and Z) and three directions (0°, 45°, and 90°). The printing directions had the largest effect on the mechanical properties when the directions caused a longer print time or a greater thermal load on the parts. The parts built in the XY BRP45 orientation and direction show an average ultimate tensile strength of 384.3 MPa and Rockwell Hardness B averages of 39.4. Based on the chemical analysis and the light and electron microscopy investigations several factors affecting the mechanical behavior of as-printed parts are grain size, manufacturing defects (voids and cracks), inclusions, and chemical segregations. Following the Hall-Petch equation there is a direct correlation between the material yield strength and grain size. In the printed parts the grain size and orientation are controlled by different cooling conditions. Conduction cooling at the interface between print and build plate creates the condition of textured structure. In this case the elongated grains are formed, with the longitudinal axes perpendicular to the build plate (XY bottom samples). In the case of Z oriented samples variation in convection cooling conditions creates different microstructure between the front and back samples. Ti-inclusions seems to be due to the printing environment, since no Ti is listed in the nominal chemical composition of the Invar 36 starting wire.

Committee: Constantin Solomon PhD (Advisor); Brian Vuksanovich PhD (Committee Member); Pedro Cortes PhD (Committee Member) Subjects: Engineering; Mechanical Engineering

Master of Science, Miami University, 2023, Mechanical and Manufacturing Engineering

Owing to their superior properties like excellent mechanical strength, thermal and oxidation resistance, chemical stability, biocompatibility, chemical resistance, etc. zirconia-based ceramics find their applications in industries, including aerospace, automotive, biomedical, energy, etc. But manufacturing parts of zirconia-based ceramic by traditional manufacturing processes like injection molding, hot pressing, cold pressing, etc., provides difficulties in fabricating high-quality parts with complex geometrical shapes. Additive manufacturing (AM) can be a solution to this problem. Various AM techniques, including binder jetting, selective laser sintering, material extrusion, etc., have been utilized to manufacture complex shapes using zirconia-based ceramic. It remains a challenge to fabricate good-quality parts using AM techniques. From the published report, it is also evident that zirconia-based ceramics show inferior mechanical properties. In this research, inkjet-based AM, which is a material extrusion-based AM technique, is used to fabricate high-quality zirconia-based ceramic. Moreover, zirconia-based ceramic is reinforced with graphene to improve mechanical, thermal, and microstructural properties, and the effects of graphene on these properties as well as on cell adhesion have been analyzed.

Committee: Dr. Yingbin Hu (Advisor); Dr. Muhammad P. Jahan (Committee Member); Dr. Jinjuan She (Committee Member) Subjects: Mechanical Engineering

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

One of the technological challenges in the widespread application of additive manufacturing is the formation of undesired material microstructure and defects. Specifically, in metal additive manufacturing, the microstructural formation of columnar grains in Ti-6Al-4V is common and results in anisotropic mechanical properties and a reduction in properties such as ductility and endurance limit. This work presents the application of hexagonal and circular arrays of synchronized lasers to alter the microstructure of Ti-6Al-4V in favor of equiaxed grains. An anisotropic heat transfer model obtains the temporal/spatial temperature distribution and constructs the solidification map for various process parameters, including laser power, laser scanning speed, and internal distance between lasers in the array. Some degree of laser overlap is recommended to maintain continuous melt pools. The results, particularly at higher power settings and lower scanning speeds, indicate the attainability of equiaxed grains, suggesting a degree of control in microstructure formation in additive manufacturing.

Committee: Hamed Attariani Ph.D. (Advisor); Nathan W. Klingbeil Ph.D. (Committee Member); Ahsan Mian Ph.D. (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy in Materials Science and Engineering, Youngstown State University, 2022, Materials Science

Common failure modes to Big Area Additive Manufacturing (BAAM) are the phenomenon of slumping and excessive distortion. Slumping or sagging usually occurs when the printed structure retains excessive heat. This phenomenon is commonly seen when the build has insufficient cooling between layers and, therefore, inadequate mechanical strength due to the high-temperature material properties to support the layers above. Distortion is the planar deviation from the desired geometry. Significant residual stresses typically distort BAAM builds. Stresses often occur due to the thermal cycling and large temperature gradients found in additively manufactured parts. This study developed a transient thermal and structural simulation model to predict the slumping phenomenon and distortion, specifically applicable to overhanging features. A pyramidal model was crafted in Ansys Workbench software to simulate a large layer overhang to investigate the necessary slumping conditions. The pyramid was designed to have 53 layers and utilized symmetry to reduce the pyramid to one-quarter of the overall size and was modeled using standard ABS material. The simulation model matches the dimensions in the experimental pyramid, which had bead dimensions of 12.5 mm wide with a thickness of 5 mm. The overall structure size was 1.06 m by 0.77 m by 0.43 m. Each layer in the model independently allows for element birth/death commands and individual layer mesh parameters. The built-in element birth/death commands enable the layers to activate and progress the same way as the experimental build. As each new layer is activated, a temperature input of 200°C is applied then turned off just as the next layer is activated. The feedstock material selected for this study is Acrylonitrile Butadiene Styrene (ABS), which was selected based on the physical properties and the availability of the temperature-dependent material properties. The availability of these temperature-dependent material properties is ess (open full item for complete abstract)

Committee: Kyosung Choo Ph.D. (Advisor); Jae Joong Ryu Ph.D. (Committee Member); Donald Priour Ph.D. (Committee Member); Brian Cockeram Ph.D. (Committee Member); Matthew Caputo Ph.D. (Committee Member) Subjects: Engineering; Materials Science; Mechanical Engineering

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

Material extrusion processes have been increasingly employed in the fabrication of advanced ceramics in the aerospace, automotive, and biomedical fields. Such processes—which involve printing compositions containing ceramic powders and sacrificial binders, debinding the binders, and sintering the parts to obtain pure ceramics—can be used to produce more complex structures than traditional ceramic manufacturing techniques. In this study, a rod-shaped feedstock comprised of binder-coated zirconia containing 87 wt% zirconia was supplied to a motorized piston extruder in a customized 3D printer to fabricate green ceramic structures, and the structures were then subjected to debinding and sintering. A comprehensive set of characteristics were examined: the thermal and rheological properties of the feedstock, the printability of the feedstock, the influence of the layer thickness and raster angle on the surface roughness and flexural/tensile/compressive strengths of the sintered zirconia, Vickers hardness, relative density and porosity, shrinkage behavior, and the micro/macro structure of green and sintered 3D-printed zirconia structures. The comprehensive characteristics of 3D printed green and sintered zirconia that were obtained in this study can facilitate the successful 3D printing of ceramics. Next, for extending the functionality and applications of parts produced by additive manufacturing, an inductive proximity sensor with a 3D-printed ceramic housing and embedded sensing elements was designed and produced using a hybrid manufacturing process in which the printing process is paused, and a sensing element is embedded into the printed structure. In the developed process, binder-coated zirconia was used to fabricate the ceramic housing for the sensor, and platinum wire was used in the sensing element. The subsequent debinding and sintering processes achieved a nearly fully dense ceramic housing that protects the sensor in harsh environments. Furthermore, zirconia fe (open full item for complete abstract)

Committee: Jae-Won Choi (Advisor); Gregory N Morscher (Committee Member); Jiang Zhe (Committee Member); Kwek-Tze Tan (Committee Member); Kye-Shin Lee (Committee Member); Sadhan C Jana (Committee Member) Subjects: Mechanical Engineering

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

Large-scale additive manufacturing (AM) capabilities is offered through the use of pulse gas metal arc directed energy deposition (P-GMA DED). This process incorporates a commercial robotic cell and gas metal arc welding apparatus to generate components additively layer by layer. The advantages of this platform include lower costs and higher deposition rates when compared to other DED processes, positioning this technology for widespread industrial adoption. To enable the digital manufacturing of a component from a computer-aided design (CAD) file, computer-aided manufacturing (CAM) solutions must generate required robot path and welding parameter commands as programs. These instructions are highly dependent on the feature and application requirements as well as material used. To this end, scalable and robot-agnostic computer-aided robotics (CAR) software is required to automate the programming for deposition. This work establishes the use of Autodesk PowerMill Ultimate software as a CAM/CAR solution for arc-based DED processes across robot manufacturers. An 8-axis OTC Daihen P-GMA robot DED welding system was converted into a DED system by modeling the robot cell (i.e. the digital twin) and coding a post-processor that compiles the PowerMill build simulation solution into the “physical” robot build plan program. P-GMA DED welding parameters were developed to produce a wide range of features and components using aluminum-magnesium alloy ER5183 filler wire material. This alloy is widely used in shipbuilding and large vehicle structures based on its good strength and weldability where large-scale DED can reduce cost and schedule. Systematic parameter development techniques were applied and developed to determine parameters for single-pass per layer “walls” and multi-pass per layer “block” features. Builds and features of increasing complexity were evaluated using different wall and block parameters. Walls and block parameter were systematically modified (open full item for complete abstract)

Committee: Boyd Panton (Committee Member); Dennis Harwig (Advisor) Subjects: Engineering; Materials Science; Metallurgy

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

In additive manufacturing (AM), it is necessary to know the influence of processing parameters in order to have better control over the microstructure and mechanical performance of the part. Laser powder bed fusion (LPBF) is a metal AM process in which thin layers of powdered material are selectively melted to create a three-dimensional structure. This manufacturing process is beneficial for many reasons; however, it is limited by the thermal solidification conditions achievable in the available processing parameter ranges for single-beam processing methods. Therefore, this work investigates the effect of multiple, coordinated heat sources, which are used to strategically modify the melting and solidifying in the AM process. The addition of multiple heat sources has the potential to provide better control of the thermal conditions, thus providing better control of the microstructure of the additively manufactured parts. To model this, existing thermal models of the LPBF process have been modified to predict the thermal effects of multiple coordinated laser beams. These computational models are used to calculate melt pool dimensions and thermal conditions throughout the LPBF process. Furthermore, the results of the simulations are used to determine the influence of the distance between the coordinated laser beams. The predictive method used in this research provides insight into the effects of using multiple coordinated beams in LPBF, which is a necessary step in increasing the capabilities of the AM process.

Committee: Joy Gockel Ph.D. (Advisor); Nathan Klingbeil Ph.D. (Committee Member); Ahsan Mian Ph.D. (Committee Member) Subjects: Mechanical Engineering

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

In this research, a designer-driven approach was utilized to construct uniform structure and density infill designs suitable for most AM technologies. Infills were designed using a selected geometry—square, hexagonal, diamond, or triangular— and a specified air gap—1mm, 3mm, 5mm, 7mm, and 9mm. By simulating a flexural test using finite element analysis (FEA), the different infill designs were assessed. The placement of infill and its effect on part performance is also discussed. These infill designs were then selectively used in regions of the flexural test specimen where there is minimal stress. The selective infill designs were subjected to the same FEA as the uniform infill designs for a comparative analysis and to assess the effect of selectively adding infill to minimize material without sacrificing performance. Test samples used in the selective infill FEA were then printed on the Stratasys Objet30 and tested for validation. Additionally, infill designs were improved by adding material to the part thickness. Material was added to the part thickness and studied to analyze the effects of this technique, and to discover more efficient methods of utilizing material in additive manufacturing. The results of this methodology proved to be an effective way to analyze the effects of infill designs commonly in additive manufacturing.

Committee: Dale Masel PhD (Advisor) Subjects: Design; Engineering

Master of Science in Materials Science and Engineering (MSMSE), Wright State University, 2018, Materials Science and Engineering

Laser based additive manufacturing of Ti-6Al-4V components is under consideration for aerospace applications. The mechanical properties of the finished components depend on their microstructure. Process mapping compares process variables such as heat source power, heat source travel speed, material feed rate, part preheat temperature and feature geometry to process outcomes such as microstructure, melt pool geometry and residual stresses. In this work, the microstructure of two-dimensional pads, multilayer pads, thin walls, and structural components at the steady state location was observed. A method for measuring β grain widths that allows for the calculation of standard deviations, confidence intervals, and variances in grain size was developed. This represents an improvement over the commonly used line-intercept method. The method was used to compare variability of β grain widths across different part geometries. It was found that thin wall parts have the highest β width variability and that the width of the β grains varies more towards the top of multi-layered samples than towards the bottom. Experimental results for α and β grain size across multiple deposit geometries are presented that offer new insight into the effect of process variables on microstructure. β grain widths are also compared for different deposit geometries with the same power, velocity, and feed rate. Single layer pad geometries were found to have the smallest β grain widths, multi-layer pads had larger β grain widths, and thin wall samples had the largest β grain widths. Trends in α width with Vickers hardness were also considered in the context of thermal gradient measurements. Hardness maps were created for the structural component samples. Optical microscopy was used to observe a layering effect in structural component samples. It was found that light and dark bands had different Vickers microhardness values.

Committee: Nathan Klingbeil Ph.D. (Advisor); Joy Gockel Ph.D. (Committee Member); Raghavan Srinivasan Ph.D. (Committee Member) Subjects: Engineering; Materials Science; Mechanical Engineering; Metallurgy

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

Significant advancements in the field of additive manufacturing (AM) have increased the popularity of AM in mainstream industries. Manufacturing feasibility and the dimensional accuracy of parts manufactured using AM depend on the part geometry and the accompanying process parameters. In order to create high quality functional products, both the part design and the process parameters need to be optimized for additive manufacturing processes. Build orientation is one of the most critical process parameters, since it has a direct impact on the part quality measurement metrics and the manufacturability concerns associated with AM. Designing parts for additive manufacturing (DFAM) and implementing those design considerations to determine the best build orientation can help achieve successful part builds. In addition to build orientation, optimization of the part designs based on DFAM principles can also significantly mitigate the manufacturability concerns in the early design stage. In this research, a weighted optimization model is presented to determine the optimum build orientation of a given part based on DFAM guidelines. These DFAM parameters include part geometric metrics such as cusp error, layer contour features such as thin features and sharp corners, and support structure parameters. A novel design optimization approach is proposed which integrates additive manufacturing constraints within a topology optimization framework. A density mapping based algorithm is developed for SIMP based topology optimization to minimize the growth of critically thin features in the optimized part design. Both these optimization models are validated with two test cases each. Improvements in the manufacturability metrics achieved using these algorithms prove the effectiveness of the proposed methodologies.

Committee: Sam Anand Ph.D. (Committee Chair); Michael Alexander-Ramos Ph.D. (Committee Member); Kumar Vemaganti Ph.D. (Committee Member) Subjects: Mechanical Engineering

MS, University of Cincinnati, 2015, Engineering and Applied Science: Mechanical Engineering

Additive Manufacturing (AM) processes are used to fabricate complex geometries using a layer by layer material deposition technique. These processes are recognized for creating complex shapes which are difficult to manufacture otherwise and for enabling designers to be more creative with their designs. However, as AM is still in its developing stages, relevant literature with respect to design guidelines for AM is not readily available. This research proposes a novel design methodology which can assist designers in creating parts with high manufacturability. The research includes formulation of design guidelines by studying the relationship between input part geometry and AM process parameters. Two approaches are considered for application of the developed design guidelines. The first approach presents a feature graph based design improvement method in which the concept of Producibility Index (PI) is used to compare the designs. This method is useful for performing manufacturing validation of pre-existing designs and modifying it for better manufacturability. The second approach presents a DFAM constrained topology optimization based design advisory which can help designers in creating entirely new lightweight designs that are additive friendly. In this approach, the developed AM design guidelines are mathematically integrated with existing structural optimization techniques. Application of both the methods is presented in the form of case studies where design improvement and evolution is observed.

Committee: Sundararaman Anand Ph.D. (Committee Chair); Sundaram Murali Meenakshi Ph.D. (Committee Member); David Thompson Ph.D. (Committee Member); Kumar Vemaganti Ph.D. (Committee Member) Subjects: Engineering

Doctor of Philosophy, The Ohio State University, 2014, Welding Engineering

Additive manufacturing is an emerging production technology used to create net shaped 3-D objects from a digital model. Ultrasonic Additive Manufacturing (UAM) is a relatively new type of additive manufacturing that uses ultrasonic energy to sequentially bond layers of metal foils at temperatures much lower than the melting temperature of the material. Constructing metal structures without melting allows UAM to have distinct advantages over beam based additive manufacturing and other traditional manufacturing processes. This is because solidification defects can be avoided, structures can be composed of dissimilar material and secondary materials (both metallic and non-metallic) can be successfully embedded into the metal matrix. These advantages allow UAM to have tremendous potential to create metal matrix composite structures that cannot be built using any other manufacturing technique. Although UAM has tremendous engineering potential, the effect of interfacial bonding defects on the mechanical and thermal properties have not be characterized. Incomplete interfacial bonding at the laminar surfaces due to insufficient welding energy can result in interfacial voids. Voids create discontinuities in the structure which change the mechanical and thermal properties of the component, resulting in a structure that has different properties than the monolithic material used to create it. In-situ thermal experiments and thermal modeling demonstrates that voids at partially bonded interfaces significantly affected heat generation and thermal conductivity in UAM parts during consolidation as well as in the final components. Using ultrasonic testing, elastic properties of UAM structures were found to be significantly reduced due to the presence of voids, with the reduction being the most severe in the transverse (foil staking) direction. Elastic constants in all three material directions decreased linearly with a reduction in the interfacial bonded area. The lin (open full item for complete abstract)

Committee: Wei Zhang PhD (Advisor); Sudarsanam Suresh Babu PhD (Committee Member); Glenn Daehn PhD (Committee Member); Stanislav Rokhlin PhD (Committee Member) Subjects: Aerospace Materials; Materials Science; Mechanical Engineering

Master of Science, The Ohio State University, 2014, Welding Engineering

Laser Engineered Net Shaping (LENS) is a solid freeform fabrication process capable of producing net shape, custom parts through a layer-by-layer deposition of material using a laser energy source. LENS based Ti-6Al-4V parts are currently being explored for applications to aerospace and biomedical implant applications. To achieve satisfactory mechanical performance in the components, homogeneity of the microstructure and the physical structure is important. This study explores methods of improving the fatigue life of Ti-6Al-4V LENS deposits through the creation of defect free components with appropriate microstructure. The work focuses on the impact of beta grain refinement and the elimination of lack of fusion porosity defects on the fatigue life of the alloy. Further, a model is developed to predict the epitaxial grain growth in LENS builds of Ti-64. This model is used to augment the prediction capability of a simultaneous transformation kinetics (STK theory) based model developed previously. The beta grain refinement in the fatigue properties of Ti-64 is achieved through addition of boron in amounts < 3 wt%. The addition of boron is found to refine the columnar beta structure typically observed in LENS deposited Ti-64. However, at high concentrations of boron, it was difficult to discern the prior beta grain size to visualize the extent of grain refinement. The boron alloying further causes a significant change in the structure of alpha laths, leading the shorter and thicker individual laths. Grain boundary alpha is not observed in the microstructure on addition of boron above a certain threshold. The addition of boron is observed to improve the fatigue properties of deposited Ti-64 samples. The Ti-64 LENS builds are observed to contain lack-of-fusion porosity in the lower regions of the deposit close to the substrate. The effect of process parameters namely the power, travel speed, hatch width, pre-heating, powder flow rate, substrate surface quality, a (open full item for complete abstract)

Committee: Wei Zhang (Advisor); Dave Farson (Committee Member); Sudarsanam Babu (Committee Member) Subjects: Materials Science

Master of Science, The Ohio State University, 2013, Materials Science and Engineering

Laser based additive manufacturing has become an enabling joining process for making one-of-a-kind parts, as well as, repairing of aerospace components. Although, the process has been established for more than a decade, optimization of the process is still performed by trial and error experimentation. At the same time, deployment of integrated process-microstructure models has remained as a challenge due to some of the reasons listed below: (1) lack of good process models to consider the laser-material interactions; (2) inability to capture all the heat transfer boundary conditions; (3) thermo-physical-mechanical properties; and (4) robust material model. This work pertains to the development of robust material model for predicting microstructure evolution as a function of arbitrary thermal cycles (multiple heating and cooling cycles) that can be integrated into a process model. This study focuses on the development of a material model for Ti-6Al-4V and Alloy 718. These two alloys are heavily used in turbine engines and undergo complex phase transformations, making them suited to developing a material model for laser metal deposition (LMD). The model uses simultaneous transformation kinetics (STK) theory to predict the transformation of one parent phase into several products. The model uses calculated thermodynamic properties of the alloys for portions of the respective transformation characteristics. Being a phenomenological model there are several user defined calibration parameters to fit the predicted output to experimental data. These parameters modify the nucleation and growth kinetics of the individual transformations. Analyses of experimental LMD builds are used to calibrate the material model. A Ti-6Al-4V build made on a room temperature substrate showed primarily colony alpha morphology in the bottom half of the build with a transition to basketweave alpha in the top half. An increase in hardness corresponding to the microstructural transition was o (open full item for complete abstract)

Committee: Sudarsanam Babu (Advisor); Wolfgang Windl (Committee Member) Subjects: Aerospace Materials; Materials Science; Metallurgy

Master of Sciences (Engineering), Case Western Reserve University, 2024, EECS - System and Control Engineering

Wire Arc Additive Manufacturing (WAAM) has emerged as a promising technology for producing metal parts, offering reduced lead times and costs compared to traditional methods. However, achieving optimal process parameters in WAAM and accurately predicting bead height remain challenging due to complex interactions between input variables and output characteristics. This thesis addresses the challenge of developing a machine learning regression model to predict the average bead height of single deposited beads, crucial for building simple and complex shapes in WAAM. The research investigates the relationship between four critical input parameters - Voltage, Wire Feed Speed (WFS), Travel Speed, Contact Tip to Work Distance (CTWD) - and their influence on bead dimensions in WAAM. A comprehensive experimental setup is employed, utilizing a custom-built WAAM 3D metal printer equipped with a gantry system and controlled by a Duet 3 controller. Steel wire ER70s-6 with a diameter of 0.9mm is used for printing, producing single beads with heights ranging from 2.5mm to 3.55mm. A total of 248 experiments are performed using the Arc-One Machine at Case Western Reserve University (CWRU) for the model training, which are then analyzed. A machine learning regression model is built using this dataset, with four inputs (Voltage, Travel Speed, Wire Feed Speed, Contact Tip to Work Distance) and two corresponding outputs (average bead height and variance of bead heights). Various analytical techniques were explored to predict the average bead height and its variance, leading to the adoption of the Gradient 18 Boosting regression model as the most effective approach. Two models, a forward model and an inverse model, were developed to predict WAAM parameters and outputs. The forward model predicts the average bead height and variance based on the input parameters (Voltage, Wire Feed Speed, Travel Speed, and Contact Tip to Work Distance), providing insights into how th (open full item for complete abstract)

Committee: Kenneth Loparo (Committee Chair); Robert Gao (Committee Member); John Lewandowski (Committee Member); Robert Gao (Committee Member); John Lewandowski (Committee Member); Kenneth Loparo (Advisor) Subjects: Aerospace Engineering; Design; Experiments; Materials Science

Master of Science, Miami University, 2025, Mechanical Engineering

Polydimethylsiloxane (PDMS), a versatile silicon-based polymer, is widely used in biomedical devices, microfluidic systems, wearable technology, and electronics due to its mechanical flexibility, optical clarity, electrical conductivity, and biocompatibility. However, its low Young's modulus and tensile strength limit its application in high-stress environments. To enhance its mechanical and functional properties, this study explores the incorporation of carbon fibers (CF) and graphene (Gr) as reinforcements. Despite the potential benefits of these nanomaterials, challenges such as aggregation, void formation, and poor interfacial bonding often compromise composite performance. This research integrates acoustic field (AF) technology into inkjet-based additive manufacturing (AM) to address these issues. The AF enhances material dispersion, reduces defects, and improves bonding between reinforcements and the PDMS matrix. The study evaluates the effects of CF and Gr reinforcements with AF treatment on the mechanical, microstructural, and dynamic properties of PDMS composites. Furthermore, it investigates the impact of different percentages of graphene content on the electrical resistance and mechanical properties graphene-reinforced-PDMS for wearable sensor applications. Results demonstrate that optimal graphene content balances dispersion and aggregation, thus, maximizing mechanical strength and electrical conductivity. By introducing AF-assisted AM, this study provides insights into producing high-performance PDMS composites for advanced applications, particularly in sensors and flexible electronics.

Committee: Muhammad Jahan (Advisor); Yingbin Hu (Committee Member); Zhijiang Ye (Committee Member); Jinjuan She (Committee Member) Subjects: Mechanical Engineering

Master of Science (M.S.), University of Dayton, 2024, Bioengineering

Electrospun nanofiber (ESNF) membranes have attracted widespread interest in many applications due to their advantages in high specific surface area, high porosity, and structural controllability. This study combines gap electrospinning and electrolyte-assisted electrospinning techniques to develop a novel electrospinning approach for producing nanofiber mats of arbitrary geometry. A 3D printed conductive gelatin-based polymer electrolyte (GPE) solution is used as a geometric collector to focus the deposition of electrospun mats. The method utilizes syringe extrusion 3D printing of the GPE solution to produce a shape upon which ESNF are focused. The printable GPE ink is formulated to ensure it possesses the necessary conductivity, shear-thinning, and thixotropic properties. We have developed a gelatin-based GPE ink, enhanced with Laponite to improve shear-thinning properties and salts to increase conductivity. The 3D printing equipment then extrudes the GPE solution on the surface of the target device according to the pre-designed pattern. The optimized GPE solution formulation contained 8% w/v gelatin, 0.2% w/v Laponite, 2 mol/L sodium chloride, and 14.3% v/v glycerol, which was shown to meet the dual requirements of 3D printing and assisting electrospinning. The ink's conductivity was 8.02 S/m measured using a custom developed four-point probe system for gels. Rheological analysis demonstrated that the ink exhibits shear thinning (fluid behavior index n=0.223), which allows GPE ink to maintain a balance between easy extrusion and structural stability. We tested the electrospinning solution used during the experiment and investigated and characterized electrospinning operating parameters to explore several relationships between unrestricted mat diameter (UMD) and electrospinning operating parameters and GPE patterning threshold. The performance of the GPE ink was thoroughly examined experimentally: under the conditions of 25°C and 26% relative humidity, the (open full item for complete abstract)

Committee: Russell Pirlo (Committee Chair); Donald Klosterman (Committee Member); Erick Vasquez (Committee Member); Li Cao (Committee Member) Subjects: Biomedical Engineering; Biomedical Research

Master of Science, Miami University, 2024, Mechanical and Manufacturing Engineering

Selective laser sintering (SLS) technique has emerged as an important method in additive manufacturing, facilitating the manufacturability of complex lattice structures, known for their high stiffness-to-weight ratios. However, these structures face mechanical limitations, such as low compressive strength and energy absorption, restricting their use in demanding industries like aerospace and automotive. This study addresses these challenges by reinforcing SLS-printed Nylon 12 (Polyamide 12, PA12) lattice structures with thermoset resins (Bisphenol A, BPA epoxy), forming layered composites that significantly improve compressive performance. A continuous rotation coating technique was introduced to overcome the uneven reinforcement observed in traditional dip-coating methods, achieving a uniform resin distribution. The optimized coating method resulted in a 13% improvement in compressive yield strength compared to dip-coated samples, contributing to an overall 139% increase relative to unreinforced PA12. Further enhancement was achieved through the incorporation of functionalized graphene nanofillers into the PA12/thermoset matrix, with the optimal configuration (68:32 PA12-to-BPA epoxy ratio with 0.1 wt% graphene) yielding a 201% increase in compressive yield strength and a 154% increase in specific energy absorption. Image analysis confirmed improved adhesion, and improved structural integrity at the samples with optimal configuration. Findings from this study provide a pathway for industrial applications of SLS-printed lattice structures, enabling lightweight, high-strength components for aerospace and automotive industries.

Committee: Muhammad Jahan (Advisor); Kumar Singh (Committee Member); Jinjuan She (Committee Member); Yingbin Hu (Committee Member) Subjects: Aerospace Materials; Automotive Materials; Engineering; Materials Science; Mechanical Engineering