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Articles 1 - 30 of 256
Full-Text Articles in Mechanical Engineering
Fatigue Behavior Of Cu-Zr Metallic Glasses Under Cyclic Loading, Nikolai Priezjev
Fatigue Behavior Of Cu-Zr Metallic Glasses Under Cyclic Loading, Nikolai Priezjev
Mechanical and Materials Engineering Faculty Publications
The effect of oscillatory shear deformation on the fatigue life, yielding transition, and flow localization in metallic glasses is investigated using molecular dynamics simulations. We study a well-annealed Cu-Zr amorphous alloy subjected to periodic shear at room temperature. We find that upon loading for hundreds of cycles at strain amplitudes just below a critical value, the potential energy at zero strain remains nearly constant and plastic events are highly localized. By contrast, at strain amplitudes above the critical point, the plastic deformation is gradually accumulated upon continued loading until the yielding transition and the formation of a shear band across …
Additively Manufactured Polymeric Surface-Based Lattice Structures For Vibration Attenuation, Imabin Kelvin Ekpelu
Additively Manufactured Polymeric Surface-Based Lattice Structures For Vibration Attenuation, Imabin Kelvin Ekpelu
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The focus of this study was to select triply periodic minimal surface (TPMS) structures made of 3D-printed polymers. The primary variables in this study were: TPMS shape, lattice volume ratio, and lattice material. Vibration absorption was characterized by damping ratio via transmissibility at the system’s natural frequency. The vibration testing was performed using an electro-dynamic shaker, a known mass, an input/control accelerometer, and an output/response accelerometer. The 3D-printed absorber/lattice was mounted to the shaker baseplate and a mass will be mounted on top of the absorber. One accelerometer will be mounted to the shaker baseplate and the other will be …
Developing Scaling Laws To Predict Compressive Mechanical Properties And Determine Geometrical Parameters Of Modified Bcc Lattice Structures, Hasanain Abdulhadi, Abdalsalam Fadeel, Tahseen A. Alwattar, Ahsan Mian
Developing Scaling Laws To Predict Compressive Mechanical Properties And Determine Geometrical Parameters Of Modified Bcc Lattice Structures, Hasanain Abdulhadi, Abdalsalam Fadeel, Tahseen A. Alwattar, Ahsan Mian
Mechanical and Materials Engineering Faculty Publications
The objective of this study is to develop generalized empirical closed-form equations to predict the compressive mechanical properties and determine geometrical parameters. To achieve that, 117 models are built and analyzed using ABAQUS/CAE 2016 to provide two types of reliable data: one for lattice mechanical properties based on finite element method and the other for geometrical parameters using the measurements of ABAQUS diagnostic tool. All the models are created by modifying the basic feature of body-centered cubic lattice structure based on a range of strut angles, a set of relative densities, and two design sets. Also, the influence of lattice …
Advances In Mechanical Metamaterials For Vibration Isolation: A Review, Mohammed Al Rifaie, Hasanain Abdulhadi, Ahsan Mian
Advances In Mechanical Metamaterials For Vibration Isolation: A Review, Mohammed Al Rifaie, Hasanain Abdulhadi, Ahsan Mian
Mechanical and Materials Engineering Faculty Publications
The adverse effect of mechanical vibration is inevitable and can be observed in machine components either on the long- or short-term of machine life-span based on the severity of oscillation. This in turn motivates researchers to find solutions to the vibration and its harmful influences through developing and creating isolation structures. The isolation is of high importance in reducing and controlling the high-amplitude vibration. Over the years, porous materials have been explored for vibration damping and isolation. Due to the closed feature and the non-uniformity in the structure, the porous materials fail to predict the vibration energy absorption and the …
Computational Investigation Of The Post-Yielding Behavior Of 3d-Printed Polymer Lattice Structures, Abdalsalam Fadeel, Hasanain Abdulhadi, Golam Newaz, Raghavan Srinivasan, Ahsan Mian
Computational Investigation Of The Post-Yielding Behavior Of 3d-Printed Polymer Lattice Structures, Abdalsalam Fadeel, Hasanain Abdulhadi, Golam Newaz, Raghavan Srinivasan, Ahsan Mian
Mechanical and Materials Engineering Faculty Publications
Sandwich structures are widely used due to their light weight, high specific strength, and high specific energy absorption. Three-dimensional (3D) printing has recently been explored for creating the lattice cores of these sandwich structures. Experimental evaluation of the mechanical response of lattice cell structures (LCSs) is expensive in time and materials. As such, the finite element analysis (FEA) can be used to predict the mechanical behavior of LCSs with many different design variations more economically. Though there have been several reports on the use of FEA to develop models for predicting the post-yielding stages of 3D-printed LCSs, they are still …
Behavior Of 3d Printed Polymeric Triply Periodic Minimal Surface (Tpms) Cellular Structures Under Low Velocity Impact Loads, Jesse James Leiffer
Behavior Of 3d Printed Polymeric Triply Periodic Minimal Surface (Tpms) Cellular Structures Under Low Velocity Impact Loads, Jesse James Leiffer
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Surface-based lattice structures such as triply periodic minimal surface (TPMS) lattices are lightweight structures that are widely being investigated for applications in automotive, aerospace, military, railway, and naval structures. Due to the recent advent of three-dimensional (3D) printing (3DP) technologies, architected cellular materials such as surface- or strut-based periodic lattice cell structures have emerged as a unique class of lightweight metamaterials. These materials possess enhanced strength to weight ratio, high stiffness, exceptional capabilities in reducing noise and vibration, insulating heat, and effective impact energy absorption. Understanding the impact behavior of such materials are important so that they can be reliably …
Simulation Of Residual Stress Generation In Additive Manufacturing Of Complex Lattice Geometries, Katie Sue Bruggeman
Simulation Of Residual Stress Generation In Additive Manufacturing Of Complex Lattice Geometries, Katie Sue Bruggeman
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Residual stresses developed during additive manufacturing (AM) can influence the mechanical performance of structural components in their intended applications. In this study, thermomechanical residual stress simulations of the laser powder bed fusion (LPBF) process are conducted for both simplified (plate and cube-shaped) geometries as well as five complex lattice geometries fabricated with Inconel 718. These simulations are conducted with the commercial software package Simufact Additive©, which uses a non-linear finite element analysis and layer-by-layer averaging approach in determining residual stresses. To verify the efficacy of the Simufact Additive© simulations, numerical results for the plate and cube-shape geometries are analyzed for …
Demonstration Of High-Temperature Operation Of Beta-Gallium Oxide (Β-Ga2o3) Metal-Oxide-Semiconductor Field Effect Transistors (Mosfet) With Electrostatic Model In Comsol, Nicholas Paul Sepelak
Demonstration Of High-Temperature Operation Of Beta-Gallium Oxide (Β-Ga2o3) Metal-Oxide-Semiconductor Field Effect Transistors (Mosfet) With Electrostatic Model In Comsol, Nicholas Paul Sepelak
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β-Ga2O3 is a robust semiconductor material set with a large band gap of ~4.8 eV, low intrinsic carrier concentration, and high melting point that offers a stable platform for operating electronic devices at high temperatures and extreme environments. The first half of this thesis will cover the fabrication of a fixture and packaging to test electronic components at high temperatures. Then it will highlight the characterization of β-Ga2O3 field effect transistors from room temperature (RT) up to 500 °C. The devices, fabricated with Ni/Au and Al2O3 gate metal-oxide-semiconductor (MOS), demonstrate stable operation up to 500 oC. The tested device shows …
A Digital Twin For Synchronized Multi-Laser Powder Bed Fusion (M-Lpbf) Additive Manufacturing, Shayna Petitjean
A Digital Twin For Synchronized Multi-Laser Powder Bed Fusion (M-Lpbf) Additive Manufacturing, Shayna Petitjean
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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 …
Development Of Improved Cfd Tools For The Optimization Of A Scramjet Engine, Francis A. Centlivre
Development Of Improved Cfd Tools For The Optimization Of A Scramjet Engine, Francis A. Centlivre
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In the present work, a plugin has been developed for use with the DoD HPCMP CREATE-AV Kestrel multi-physics solver that adds volumetric source terms to the energy equation. These source terms model the heat released due to combustion, but are much more computationally efficient than a full chemistry model. A thrust-based optimization study was then carried out under the control of Sandia National Laboratories' Dakota toolkit. Dakota was allowed to control the amount of heat added to three regions of the scramjet combustor. The plugin was then extended to consider ignition delay time. By comparing ignition delay time to dwell …
Printing, Characterization, And Mechanical Testing Of Additively Manufactured Refractory Metal Alloys, Brianna M. Sexton
Printing, Characterization, And Mechanical Testing Of Additively Manufactured Refractory Metal Alloys, Brianna M. Sexton
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Refractory metal alloys in the tungsten molybdenum rhenium ternary system were additively manufactured using laser power bed fusion. Four ternary alloys with varying concentrations of tungsten, molybdenum, and rhenium were manufactured and manufactured again with an addition of 1 wt% hafnium carbide. Samples were heat treated to heal cracks, reduce porosity, and reduce inhomogeneity. Material microstructure was characterized before and after heat treatment using microscopy, energy dispersive x-ray spectroscopy, and electron backscatter diffraction mapping. Mechanical testing was conducted on both three-point bend specimens and compression specimens, resulting in maximum bending strengths of 677.86 MPa, and maximum compression 0.2% yield strengths …
Molecular Dynamics Simulation Study Of A Polymer Droplet Transport Over An Array Of Spherical Nanoparticles, Anish Thomas
Molecular Dynamics Simulation Study Of A Polymer Droplet Transport Over An Array Of Spherical Nanoparticles, Anish Thomas
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This study uses molecular dynamics simulations to evaluate the dynamic behavior of a partially wetting polymer droplet driven over a nanostructured interface. We consider the bead-spring model to represent a polymeric liquid that partially wets a rough surface composed of a periodic array of spherical particles. Results show that at sufficiently small values of external force, the droplet remains pinned at the particle's surface, whereas above the threshold its motion consists of alternating periods of pinning and rapid displacements between neighboring particles. The latter process involves large periodic variation of the advancing and receding contact angles due to the attachment …
Hypersonic Conceptual Design Tool Comparison, James G. Wnek
Hypersonic Conceptual Design Tool Comparison, James G. Wnek
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The many iterations needed to explore a design space in the conceptual design process preclude the use of time-consuming RANS CFD for all but a few flight conditions. This research focuses on identifying the level of fidelity needed to adequately predict the aerothermodynamic characteristics of hypersonic vehicles. Three tools with differing levels of fidelity – CBAERO, Cart3D, and Kestrel – were used to analyze the Generic Hypersonic Vehicle (GHV) at the design condition of Mach 5.85 and an off-design condition of Mach 4.5. The results are representative of the different design tools but are not definitive due to the mesh …
Vibration Bending Fatigue Analysis Of Additively Repaired Ti-6al-4v Airfoil Blades, Lucas Jordan Smith
Vibration Bending Fatigue Analysis Of Additively Repaired Ti-6al-4v Airfoil Blades, Lucas Jordan Smith
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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 …
Design Of A Surrogate Hypersonic Inlet For The Hifire-6 Configuration, Joseph W. Mileski
Design Of A Surrogate Hypersonic Inlet For The Hifire-6 Configuration, Joseph W. Mileski
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Shock wave-boundary layer interactions can significantly impact the operability of high-speed inlets by inducing flow separation. This flow separation is difficult to visualize in three-dimensional, inward-turning inlets because of the curved surfaces that form their internal flow paths. To remedy this challenge, a surrogate test article was created. Using the results from a previously completed Computational Fluid Dynamic (CFD) analysis of the HIFiRE-6, a surrogate inlet with a rectangular isolator section was streamline-traced, allowing for the use of schlieren imagery to capture the separation bubble. This thesis discusses the process of developing the test article. Experimental results from a planned …
Development Of A Combined Thermal Management And Power Generation System Using A Multi-Mode Rankine Cycle, Nathaniel M. Payne
Development Of A Combined Thermal Management And Power Generation System Using A Multi-Mode Rankine Cycle, Nathaniel M. Payne
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Two sub-systems that present a significant challenge in the development of high performance air vehicle exceeding speeds of Mach 5 are the power generation and thermal management sub-systems. The air friction experienced at high speeds, particularly around the engine, generates large thermal loads that need to be managed. In addition, traditional jet engines do not operate at speeds greater than Mach 3, therefore eliminating the possibility of a rotating power generator. A multi-mode water-based Rankine cycle is an innovative method to address both of these constraints of generating power and providing cooling. Implementing a Rankine cycle-based system allows for the …
Development Of A Robust And Tunable Aircraft Guidance Algorithm, Jacob R. Spangenberg
Development Of A Robust And Tunable Aircraft Guidance Algorithm, Jacob R. Spangenberg
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A set of guidance control laws is developed for application to a reduced order dynamic aircraft model. A feedback control formulation utilizing a linear quadratic regulator (LQR) is developed, together with methods for easing the design burden associated with gain tuning. Metrics are developed to assess the stability margin of the controller over the full flight envelope of a notional unmanned aerial vehicle (UAV) model. A feedforward control path is then added to the architecture. The performance of the guidance control laws is assessed through time domain step response metrics as well as through execution of a design mission. The …
Development Of A Robust And Tunable Aircraft Guidance Algorithm, Jacob R. Spangenberg
Development Of A Robust And Tunable Aircraft Guidance Algorithm, Jacob R. Spangenberg
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A set of guidance control laws is developed for application to a reduced order dynamic aircraft model. A feedback control formulation utilizing a linear quadratic regulator (LQR) is developed, together with methods for easing the design burden associated with gain tuning. Metrics are developed to assess the stability margin of the controller over the full flight envelope of a notional unmanned aerial vehicle (UAV) model. A feedforward control path is then added to the architecture. The performance of the guidance control laws is assessed through time domain step response metrics as well as through execution of a design mission. The …
Performance Of A Dual Plane Airfoil Model With Varying Gap, Stagger, And Decalage Using Pressure Measurements And Particle Image Velocimetry, Salome Kenneth Nunes
Performance Of A Dual Plane Airfoil Model With Varying Gap, Stagger, And Decalage Using Pressure Measurements And Particle Image Velocimetry, Salome Kenneth Nunes
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The dual-plane airfoil has been adopted in the design of aircraft wings, wind turbine blades, and propellers. The purpose of this research is to investigate the most important design parameters of a dual-plane airfoil model for the best aerodynamic performance, such as gap, stagger, and decalage. The dual-plane airfoil model was designed using the S826 profile. A mechanical mechanism with electrical actuator control is particularly designed to alter the gap and stagger smoothly, as well as the angle of attack (AOA) for each airfoil. It results in a gap range of 1.38c to 2.17c, a stagger range of -0.75c to …
Contact Fatigue Of Spur Gear Operating Under Starved Lubrication Condition, Aparna Udthala
Contact Fatigue Of Spur Gear Operating Under Starved Lubrication Condition, Aparna Udthala
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This study describes contact fatigue behavior of spur gear contacts operating under mixed elastohydrodynamic condition. The focus is placed on the starvation effect on fatigue crack initiation. With the model, parametric simulations are carried out with different contact parameters. In the process, the lubricant supply is varied to alter the lubrication condition from fully flooded to severely starved circumstance. Multi-axial stress fields induced by surface normal and tangential tractions are evaluated, whose amplitudes and means are used in a multi-axial fatigue criterion to determine the crack initiation life. It is found a lower lubricant viscosity elongates fatigue life when severe …
Numerical Investigation Of Flow Around A Deformed Vacuum Lighter-Than-Air Vehicle, Jared N. Kerestes
Numerical Investigation Of Flow Around A Deformed Vacuum Lighter-Than-Air Vehicle, Jared N. Kerestes
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This study characterizes the functional dependence of drag on Reynolds number for a deformed vacuum lighter-than-air vehicle. The commercial computational fluid dynamics (CFD) code, FLUENT, is used to preform large eddy simulations (LES) over a range of Reynolds numbers; only Reynolds numbers less than 310,000 are considered. While the overarching goal is drag characterization, general flow-field physics are also discussed, including basic turbulence spectra. All large eddy simulations are preceded by a Reynolds-averaged Navier-Stokes (RANS) simulation using Menter’s shear stress transport (SST) model. The precursor RANS simulation serves to (1) provide realistic initial conditions, (2) decrease the time needed to …
Cooling Under Applied Stress Rejuvenates Amorphous Alloys And Enhances Their Ductility, Nikolai Priezjev
Cooling Under Applied Stress Rejuvenates Amorphous Alloys And Enhances Their Ductility, Nikolai Priezjev
Mechanical and Materials Engineering Faculty Publications
The effect of tensile stress applied during cooling of binary glasses on the potential energy states and mechanical properties is investigated using molecular dynamics simulations. We study the three-dimensional binary mixture that was first annealed near the glass transition temperature and then rapidly cooled under tension into the glass phase. It is found that at larger values of applied stress, the liquid glass former freezes under higher strain and its potential energy is enhanced. For a fixed cooling rate, the maximum tensile stress that can be applied during cooling is reduced upon increasing initial temperature above the glass transition point. …
Developing An Equivalent Solid Material Model For Bcc Lattice Cell Structures Involving Vertical And Horizontal Struts, Tahseen A. Alwattar, Ahsan Mian
Developing An Equivalent Solid Material Model For Bcc Lattice Cell Structures Involving Vertical And Horizontal Struts, Tahseen A. Alwattar, Ahsan Mian
Mechanical and Materials Engineering Faculty Publications
In this study, a body-centered cubic (BCC) lattice unit cell occupied inside a frame structure to create a so-called “InsideBCC” is considered. The equivalent quasi-isotropic properties required to describe the material behavior of the InsideBCC unit cell are equivalent Young’s modulus ( E e ) , equivalent shear modulus ( G e ) , and equivalent Poisson’s ratio ( ν e ) . The finite element analysis (FEA) based computational approach is used to simulate and calculate the mechanical responses of InsideBCC unit cell, which are the mechanical responses of the equivalent solid. Two separates finite element models are then …
Additive Manufacturing And How 3d Printing Is Fighting Covid-19, Raghavan Srinivasan, Ahsan Mian, Joy Gockel, Laura M. Luehrmann
Additive Manufacturing And How 3d Printing Is Fighting Covid-19, Raghavan Srinivasan, Ahsan Mian, Joy Gockel, Laura M. Luehrmann
Mechanical and Materials Engineering Faculty Publications
This is the fourth installment in the Shelter in Place (SiP) Lecture series. This installment covers the creative ways that 3D printing has supported efforts to combat the pandemic. It covers the basics of what 3D printing is, some of the various creative projects that have used 3D printing to combat the pandemic, among other topics and questions by the pandemic.
Correlating In-Situ Monitoring Data With Internal Defects In Laser Powder Bed Fusion Additive Manufacturing, Andrew J. Harvey
Correlating In-Situ Monitoring Data With Internal Defects In Laser Powder Bed Fusion Additive Manufacturing, Andrew J. Harvey
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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 …
Characteristics Of Nanosilver Ink (Utdag) Microdroplets And Lines On Polyimide During Inkjet Printing At High Stage Velocity, Aamir Hamad, Adam Archacki, Ahsan Mian
Characteristics Of Nanosilver Ink (Utdag) Microdroplets And Lines On Polyimide During Inkjet Printing At High Stage Velocity, Aamir Hamad, Adam Archacki, Ahsan Mian
Mechanical and Materials Engineering Faculty Publications
The performance of printed electronics strongly depends on printing techniques and printing resolution that enhance their electrical and mechanical properties. In this research paper, a Jetlab 4xl was used to control and dispense microdroplets of highly conductive nanosilver ink (UTDAg) on a polyimide substrate. The waveform effect on the droplet generation is characterized by measuring the size and the speed of the drops. The behavior of ejected drops on the substrate is studied by printing lines at different drop spacing and stage velocity. The jetting parameters that drive the piezoelectric actuator were properly determined and two waveforms (bipolar) were created …
The Effect Of Thermal History On The Atomic Structure Andmechanical Properties Of Amorphous Alloys, Nikolai V. Priezjev
The Effect Of Thermal History On The Atomic Structure Andmechanical Properties Of Amorphous Alloys, Nikolai V. Priezjev
Mechanical and Materials Engineering Faculty Publications
The influence of thermal processing on the potential energy, atomic structure, and mechanical properties of metallic glasses is examined using molecular dynamics simulations. We study the three-dimensional binary mixture, which was first relaxed near the glass transition temperature and zero pressure, and then rapidly cooled deep into the glass phase. It was found that glasses annealed at higher temperatures are relocated to higher energy states and their average glass structure remains more disordered, as reflected in the height of the first two peaks in the pair distribution function. The results of mechanical testing demonstrate that both the shear modulus and …
Thermal Modeling Of Coordinated Multi-Beam Additive Manufacturing, Rachel Elizabeth Evans
Thermal Modeling Of Coordinated Multi-Beam Additive Manufacturing, Rachel Elizabeth Evans
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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 …
Defect Modeling And Vibration-Based Bending Fatigue Of Additively Manufactured Inconel 718, Wesley Earl Eldt
Defect Modeling And Vibration-Based Bending Fatigue Of Additively Manufactured Inconel 718, Wesley Earl Eldt
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Additive manufacturing (AM) is convenient for building components with complex features. However, the long-term integrity of these components is uncertain, since AM parts have defects such as pores and rough surfaces. In this work, an analytical model was developed to determine the impact of defects, and a novel bending fatigue test was used to determine the fatigue life of channeled specimens. The analytical model, based off the theory of critical distances, investigates coupled pores and predicts their potential for fatigue failure. This resulted in a maximum allowable pore size and spacing recommendation for coupled defects. Additionally, specimens with through channels …
Adaptive Multi-Fidelity Modeling For Efficient Design Exploration Under Uncertainty, Atticus J. Beachy
Adaptive Multi-Fidelity Modeling For Efficient Design Exploration Under Uncertainty, Atticus J. Beachy
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This thesis work introduces a novel multi-fidelity modeling framework, which is designed to address the practical challenges encountered in Aerospace vehicle design when 1) multiple low-fidelity models exist, 2) each low-fidelity model may only be correlated with the high-fidelity model in part of the design domain, and 3) models may contain noise or uncertainty. The proposed approach approximates a high-fidelity model by consolidating multiple low-fidelity models using the localized Galerkin formulation. Also, two adaptive sampling methods are developed to efficiently construct an accurate model. The first acquisition formulation, expected effectiveness, searches for the global optimum and is useful for modeling …