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Articles 61 - 81 of 81
Full-Text Articles in Mechanical Engineering
Fabrication And Characterization Of Advanced Materials Using Laser Metal Deposition From Elemental Powder Mixture, Xueyang Chen
Fabrication And Characterization Of Advanced Materials Using Laser Metal Deposition From Elemental Powder Mixture, Xueyang Chen
Doctoral Dissertations
"Over the past decades of years, a great deal of money has been spent to machine large and complex parts from high-performance metals (i.e., titanium components for aerospace applications), so users attempt to circumvent the high cost of materials. Laser metal deposition (LMD) is an additive manufacturing technique capable of fabricating complicated structures with superior properties. This dissertation aims to improve the applications of LMD technique for manufacturing metallic components by using various elemental powder mixture according to the following three categories of research topics. The first research topic is to investigate and develop a cost-effective possibility by using elemental …
Laser Foil Printing And Surface Polishing Processes, Chen Chen
Laser Foil Printing And Surface Polishing Processes, Chen Chen
Doctoral Dissertations
"A foil-based additive manufacturing technology for fabricating metal parts, called Laser Foil Printing (LFP), was proposed and developed in this dissertation. The manufacturing sub-processes comprising the LFP technology were comprehensively studied, which include the laser spot welding of foil, laser raster-scan welding of foil, laser cutting of foil, and laser polishing processes. The fabricated free-form parts were demonstrated and own better mechanical properties (micro hardness and tensile strength) than the raw material, because of the rapid-cooling process of laser welding. The full and strong bond between layers was formed by the laser welding process, with no micro-cracks or pores observed. …
Research On Additive Manufacturing Of Metallic Glass Alloy, Yiyu Shen
Research On Additive Manufacturing Of Metallic Glass Alloy, Yiyu Shen
Doctoral Dissertations
"The required rapid cooling has limited the dimension of the Bulk Metallic glasses (BMGs) produced by traditional method, and hence has seriously limited their applications, despite their remarkable mechanical properties. In this present project, a detailed study is conducted on the methodology and understanding of manufacturing large Zr- based metallic glass part by laser based additive manufacturing technology, which breaks the size limitation. The first research issue proposes and develops a new additive manufacturing technology, named Laser-Foil-Printing (LFP). Sheet foils of LM105 (Zr52.5Ti5Al10Ni14.6Cu17.9 (at. %)) metallic glass are used as feed …
Investigation Of Microstructure And Mechanical Properties By Direct Metal Deposition, Jingwei Zhang
Investigation Of Microstructure And Mechanical Properties By Direct Metal Deposition, Jingwei Zhang
Doctoral Dissertations
"Microstructure and properties of Direct Metal Deposition (DMD) parts are very crucial to meeting industrial requirements of parts quality. Prediction, and control of microstructure and mechanical properties have attracted much attention during conventional metal manufacturing process under different conditions. However, there is few investigations focused on microstructure simulation and mechanical properties control under different process parameters during DMD process. This dissertation is intended to develop a multiscale model to investigate Ti6Al4V grain structure development and explore Ti6Al4V based functionally graded material (FGM) deposit properties during DMD process. The first research topic is to investigate and develop a cellular automaton-finite element …
High Temperature Polymer Composites Using Out-Of-Autoclave Processing, Sudharshan Anandan
High Temperature Polymer Composites Using Out-Of-Autoclave Processing, Sudharshan Anandan
Doctoral Dissertations
"High performance polymer composites possess high strength-to-weight ratio, corrosion resistance, and have design flexibility. Carbon/epoxy composites are commonly used aerospace materials. Bismaleimide based composites are used as a replacement for epoxy systems at higher service temperatures. Aerospace composites are usually manufactured, under high pressure, in an autoclave which requires high capital investments and operating costs. In contrast, out-of-autoclave manufacturing, specifically vacuum-bag-only prepreg process, is capable of producing low cost and high performance composites. In the current study, out-of-autoclave processing of high temperature carbon/bismaleimide composites was evaluated. The cure and process parameters were optimized. The properties of out-of-autoclave cured laminates compared …
Modeling And Characterization Of Thermo-Oxidative Behavior Of Bismaleimide Composites, Rafid Muhammad Hussein
Modeling And Characterization Of Thermo-Oxidative Behavior Of Bismaleimide Composites, Rafid Muhammad Hussein
Doctoral Dissertations
"High-temperature polymer matrix composites (HTPMCs) are susceptible to thermo-oxidation, which accelerates the composites' degradation and reduces the service life. Mechanical properties of HTPMCs deteriorate due to coupled thermo-oxidation and cross-linking mechanisms. Bismaleimides (BMIs) are commonly used high-temperature resins for aerospace applications. This work presents the viability of using experimental weight loss to model the spatial distribution of oxidation when the oxidized polymer matrix is not discernible. Three tasks are introduced: (1) Anisotropic oxidation prediction using optimized weight loss behavior of bismaleimide composites, (2) A multi-scale modeling of thermo-oxidative effects on the flexural behavior of cross-ply bismaleimide composites, and (3) Thermo-oxidative …
Modeling And Simulation Of Viscoplasticity, Recrystallization, And Softening Of Alloyed Steel During Hot Rolling Process, Xin Wang
Doctoral Dissertations
"Hot rolling is one of the most important and complex deformation processes in steel manufacturing and is essential to final product quality. The objective of this study is to investigate viscoplasticity, dynamic recrystallization, and static softening of alloyed metal during hot rolling process. Gleeble hot compression tests were performed to provide experimental stress-strain curves at different temperatures and strain rates. An inverse finite element analysis was performed to calibrate the experimental curves. Viscoplastic models including a Johnson-Cook (JC) model, a Zerilli-Armstrong (ZA) model, and a combined JC and ZA model were developed. Dynamic recrystallization behavior was investigated and modeled based …
Soy-Based Polyurethane Foam For Insulation And Structural Applications, Gurjot S. Dhaliwal
Soy-Based Polyurethane Foam For Insulation And Structural Applications, Gurjot S. Dhaliwal
Doctoral Dissertations
"Polyurethane (PU) foams are widely used as insulation materials due to their high insulation properties and low cost compared to conventional materials such as styrene and mineral wool. PU foams are traditionally fabricated with petroleum-based precursors. However, high crude price and higher carbon footprint has lead interest of researchers to synthesis PU foams using plant-based raw materials, that are inexpensive and renewable. In this dissertation, PU foams were fabricated using soy-based polyol and its thermal and mechanical properties were investigated. In the first part, of PU foam samples with different formulations were fabricated using soy-based polyol HB230, and varying amounts …
Direct Printing Of Single-Crystal Silicon By Microscale Nanoparticle Printing And Confined Laser Melting And Crystallization, Wan Shou
Doctoral Dissertations
"The transport and interfacial phenomena in laser melting and crystallization of silicon in micro-/nano-scale confinement lacks sufficient understanding. Uncovering the underlying mechanisms, and hence harness the melting and crystallization processes can help the formation of controllable single-crystal structures or patterns. In this dissertation, a molecular dynamics (MD) simulation was conducted to calculate the interfacial free energy of the silicon system in contact with flat and structured walls. Then the calculated interfacial energies were employed to predict the nucleation mechanisms in a slab of liquid silicon confined by two walls and compared with MD simulation results. Further, in combination with a …
Design For Optical Metamaterial Design For Optical Metamaterial Absorber, Huixu Deng
Design For Optical Metamaterial Design For Optical Metamaterial Absorber, Huixu Deng
Doctoral Dissertations
“Optical metamaterlal (MM) absorbers in the visible or near-infrared range have been widely investigated in these years since they are crucial in many promising applications, such as solar energy harvesting systems, thermo-photovoltaic energy conversion devices, thermal imaging and emissivity control. This dissertation aims to design and investigate various optical metamaterial absorbers based on different mechanisms and theories, such as cavity resonance, impedance match, equivalent circuit model and waveguide stop light mode. First, via utilizing the cavity resonance, a tunable narrowband MM absorber/emitter for thermophotovoltaic (TPV) is designed and analyzed based on gold nanowire cavities to improve the overall efficiency of …
Quantitative Phase-Field Modeling Of Crack Propagation In Multi-Phase Materials, Arezoo Emdadi
Quantitative Phase-Field Modeling Of Crack Propagation In Multi-Phase Materials, Arezoo Emdadi
Doctoral Dissertations
”Research presented in this dissertation is focused on developing and validating a computational framework for study of crack propagation in polycrystalline composite ceramics capable of designing micro-architectures of phases to improve fracture toughness and damage tolerance of ZrB2-based ultra-high temperature ceramics (UHTCs). A quantitative phase-field model based on the regularized formulation of Griffith’s theory is presented for crack propagation in homogenous and heterogeneous brittle materials. This model utilizes correction parameters in the total free energy functional and mechanical equilibrium equation within the crack diffusive area to ensure that the maximum stress in front of the crack tip is …
Laser-Aided Additive Manufacturing Of Glass, John Michael Hostetler
Laser-Aided Additive Manufacturing Of Glass, John Michael Hostetler
Masters Theses
“This thesis presents various approaches for the laser-aided additive manufacturing of glass. First, a technique is investigated to create free-form, low to zero coefficient of thermal expansion structures out of silica-gel. A CO2 laser was coupled through a gantry system and focused onto a binder-free silica-gel powder bed (15-40 μm particles). Prior to writing each layer, powder is dispensed by sifting it onto the build platform as opposed to a conventional wiper system, avoiding contacting and potentially damaging sensitive parts. After deposition, the parts are annealed in a furnace to increase their strength. The influence of various process parameters …
Behavior Of Eb Frp Masonry Bond Under Service Temperature, Zuhair Al-Aljaberi, John J. Myers, K. Chandrashekhara
Behavior Of Eb Frp Masonry Bond Under Service Temperature, Zuhair Al-Aljaberi, John J. Myers, K. Chandrashekhara
Civil, Architectural and Environmental Engineering Faculty Research & Creative Works
The interest in advanced composites in repairing and strengthening infrastructure systems has considerably increased, especially as the application externally bonded (EB) fiber reinforced polymer (FRP) has become more well established. Previous research on bond behavior has focused on impact of durability by considering exposure to harsh environmental conditions and testing the specimens after exposure, rather than testing bond performance during exposure. The influence of directly applying temperature on bond behavior represents an open topic that needs to be investigated in more detail. This study is one of the first studies to investigate the bond behavior when the composite is subjected …
Controlling Phase Fractions Of 304l-Ss In Selective Laser Melting Using Cooling Rate, Eberechukwu Anthony Okoro
Controlling Phase Fractions Of 304l-Ss In Selective Laser Melting Using Cooling Rate, Eberechukwu Anthony Okoro
Masters Theses
"This study examines the thermal profile and the ferrite-austenite phase fractions upon heating and cooling of 304- stainless steel powder via Selective Laser Melting (SLM). Experiments were performed to validate the ABAQUS finite element model, while the phase transformation simulation was performed using MatCalc and ThermoCalc. A correlation between the thermo-mechanical changes in ABAQUS and the microstructural changes from MatCalc was obtained by matching their cooling rates. The result indicates that cooling rate has a significant effect on the phase fractions of FCC and BCC formed in 304L stainless steel via the SLM process. The results also indicate that for …
Investigation Of The Information Provided By Light Touch For Balance Improvement In Humans, Anirudh Saini
Investigation Of The Information Provided By Light Touch For Balance Improvement In Humans, Anirudh Saini
Masters Theses
"This study investigates the information provided by Light Touch (LT) in improving human postural stability without mechanical assistance. Light Touch, an interaction force with a magnitude about 1 N, is known to improve postural stability in humans during quiet standing. However, the nature of the information from LT that helped improve balance is yet unknown. In this work, we hypothesized that LT provides information about one's body kinematics. We used a haptic robot to provide modulated, measurable light interaction force on the high back haptic location of humans to provide body kinematics-dependent information through LT. Standing balance experiments were performed …
Computational Investigation Of Polymer Electrolyte Membrane Fuel Cell With Nature-Inspired Fibonacci Spiral Flow Field, Suleyman Kose
Computational Investigation Of Polymer Electrolyte Membrane Fuel Cell With Nature-Inspired Fibonacci Spiral Flow Field, Suleyman Kose
Masters Theses
"Polymer electrolyte membrane fuel cells (PEMFC) are promising clean energy devices. The flow field design has crucial role in PEMFC performance for effective distribution of reactants and removal of products. Several nature-inspired flow field designs have recently been proposed in the literature. Common characteristics of these designs were sudden changes in the flow direction through sharp bends and flow field geometries restrained to areas having corners. In this thesis, Fibonacci spiral configuration, which is found in the nature from hurricanes to seashells, was considered for flow field pattern of a PEMFC. Contrary to the bio-inspired designs proposed in previous studies, …
Designed Extrudate For Ceramic Additive Manufacturing, Devin Mcmillen
Designed Extrudate For Ceramic Additive Manufacturing, Devin Mcmillen
Masters Theses
"The objective of this thesis work was to design ceramic paste systems that assist in achieving a high theoretical density ( > 95%) after deposition by a novel additive manufacturing process, i.e. Ceramic On-Demand Extrusion (CODE). The work is encompassed in five main sections: Sections 1 and 2 provide an introduction and literature review of relevant topics for the following sections of experimentation. Section 3 provides an analysis of a reaction chemistry to identify three discrete materials that could be combined via CODE and result in zirconium diboride (ZrB2) post-sintering. Section 4 describes the development of a high solids …
Smart Augmented Reality Instructional System For Mechanical Assembly, Ze-Hao Lai
Smart Augmented Reality Instructional System For Mechanical Assembly, Ze-Hao Lai
Masters Theses
"Quality and efficiency are pivotal indicators of a manufacturing company. Many companies are suffering from shortage of experienced workers across the production line to perform complex assembly tasks such as assembly of an aircraft engine. This could lead to a significant financial loss. In order to further reduce time and error in an assembly, a smart system consisting of multi-modal Augmented Reality (AR) instructions with the support of a deep learning network for tool detection is introduced. The multi-modal smart AR is designed to provide on-site information including various visual renderings with a fine-tuned Region-based Convolutional Neural Network, which is …
Advanced Process To Embed Optical Fiber Sensors Into Casting Mold For Smart Manufacturing, Raghavender Reddy Jakka
Advanced Process To Embed Optical Fiber Sensors Into Casting Mold For Smart Manufacturing, Raghavender Reddy Jakka
Masters Theses
"Optical fiber sensors embedded in metals with distributed sensing can sense temperature at multiple points with single fiber. This is useful for smart manufacturing like structural health monitoring in aerospace industry and smart molds in manufacturing plants. There is a huge difference in thermal coefficient of expansion for fiber and metal. This is the reason for the increase in sensitivity for embedded fiber sensors. However, at high temperatures, the stress on the fiber increases, eventually damaging the sensor. The fiber-metal interface determines the sensor performance. A tight interface results in high sensitivity and a gap in the interface enhances sensing …
Multiscale Approaches Toward Advanced Lithium-Ion Battery: From Nano To Meso Scale, Susmita Sarkar
Multiscale Approaches Toward Advanced Lithium-Ion Battery: From Nano To Meso Scale, Susmita Sarkar
Masters Theses
“Battery performance and its degradation are determined by various aspects such as the transport of ions and electrons through heterogeneous internal structures composed of constituent particles, kinetic reactions at the interfaces, and a corresponding interplay between mechanical, chemical, and thermal responses. Further, modern battery materials require a variety of engineering processes such as coating, doping and mixing. As a result, in order to fully understand the behavior of the battery material and improve battery performance, it is necessary to understand and control the individual particle behavior and then connect it to the electrode. This study elucidated the physical phenomena associated …
Enhancement Of Performance Of Micro Direct Ethanol Fuel Cells By Structural Modification, Sindhuja Valluri
Enhancement Of Performance Of Micro Direct Ethanol Fuel Cells By Structural Modification, Sindhuja Valluri
Masters Theses
“Direct Ethanol Fuel Cells (DEFC’s) are becoming more important in current energy conversion devices because of their higher efficiency compared to other fuel cells. However, the performance of current DEFC’s is not efficient in providing energy to meet increasing energy demand. The objective of this work is to make the cell compact and at the same time improve performance. For this purpose, we have removed gasket and endplates to make structure compact and increased surface area by developing a new corrugated structure. This work also uses 3D printing technology Fused Deposition Modeling (FDM) to make pocket backing case to improve …