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Articles 1 - 23 of 23
Full-Text Articles in Mechanical Engineering
Structural Transformations In Porous Glasses Under Mechanical Loading. Ii. Compression, Nikolai V. Priezjev, Maxim A. Makeev
Structural Transformations In Porous Glasses Under Mechanical Loading. Ii. Compression, Nikolai V. Priezjev, Maxim A. Makeev
Mechanical and Materials Engineering Faculty Publications
The role of porous structure and glass density in response to compressive deformation of amorphous materials is investigated via molecular dynamics simulations. The disordered, porous structures were prepared by quenching a high-temperature binary mixture below the glass transition into the phase coexistence region. With decreasing average glass density, the pore morphology in quiescent samples varies from a random distribution of compact voids to a porous network embedded in a continuous glass phase. We find that during compressive loading at constant volume, the porous structure is linearly transformed in the elastic regime and the elastic modulus follows a power-law increase as …
Slow Relaxation Dynamics In Binary Glasses During Stress-Controlled, Tension-Compression Cyclic Loading, Nikolai V. Priezjev
Slow Relaxation Dynamics In Binary Glasses During Stress-Controlled, Tension-Compression Cyclic Loading, Nikolai V. Priezjev
Mechanical and Materials Engineering Faculty Publications
The effect of cyclic loading on relaxation dynamics and mechanical properties of metallic glasses is studied using molecular dynamics simulations. We consider the Kob-Andersen three-dimensional binary mixture rapidly cooled across the glass transition and subjected to thousands of tension-compression cycles in the elastic range. It was found that during cyclic loading at constant pressure, the system is relocated to progressively lower levels of the potential energy, thus promoting greater densification and higher strength. Furthermore, with increasing stress amplitude, the average glass density increases and the minimum of the potential energy becomes deeper, while the elastic modulus is reduced. The typical …
The Critical Pressure For Microfiltration Of Oil-In-Water Emulsions Using Slotted-Pore Membranes, Nikolai V. Priezjev, Tohid Darvishzadeh, Bishal Bhattarai
The Critical Pressure For Microfiltration Of Oil-In-Water Emulsions Using Slotted-Pore Membranes, Nikolai V. Priezjev, Tohid Darvishzadeh, Bishal Bhattarai
Mechanical and Materials Engineering Faculty Publications
The influence of geometrical parameters and fluid properties on the critical pressure of permeation of an oil micro-droplet into a slotted pore is studied numerically by solving the Navier-Stokes equations. We consider a long slotted pore, which is partially blocked by the oil droplet but allows a finite permeate flux. An analytical estimate of the critical permeation pressure is obtained from a force balance model that involves the drag force from the flow around the droplet and surface tension forces as well as the pressure variation inside the pore. It was found that numerical results for the critical pressure as …
Structural Transformations In Porous Glasses Under Mechanical Loading. I. Tension, Nikolai V. Priezjev, Maxim A. Makeev
Structural Transformations In Porous Glasses Under Mechanical Loading. I. Tension, Nikolai V. Priezjev, Maxim A. Makeev
Mechanical and Materials Engineering Faculty Publications
The evolution of porous structure and mechanical properties of binary glasses under tensile loading were examined using molecular dynamics simulations. We consider vitreous systems obtained in the process of phase separation after a rapid isochoric quench of a glass-forming liquid to a temperature below the glass transition. The porous structure in undeformed samples varies from a connected porous network to a random distribution of isolated pores upon increasing average glass density. We find that at small strain, the elastic modulus follows a power-law dependence on the average glass density and the pore size distribution remains nearly the same as in …
The Yielding Transition In Periodically Sheared Binary Glasses At Finite Temperature, Nikolai V. Priezjev
The Yielding Transition In Periodically Sheared Binary Glasses At Finite Temperature, Nikolai V. Priezjev
Mechanical and Materials Engineering Faculty Publications
Non-equilibrium molecular dynamics simulations are performed to investigate the dynamic behavior of three-dimensional binary glasses prepared via an instantaneous quench across the glass transition. We found that with increasing strain amplitude up to a critical value, the potential energy approaches lower minima in steady state, whereas the amplitude of shear stress oscillations becomes larger. Below the yielding transition, the storage modulus dominates the mechanical response, and the gradual decay of the potential energy over consecutive cycles is accompanied by reduction in size of transient clusters of atoms with large nonaffine displacements. In contrast, above the yield strain, the loss modulus …
Aligned Carbon Nanotube Arrays Bonded To Solid Graphite Substrates: Thermal Analysis For Future Device Cooling Applications, Betty T. Quinton, Levi Elston, James D. Scofield, Sharmila M. Mukhopadhyay
Aligned Carbon Nanotube Arrays Bonded To Solid Graphite Substrates: Thermal Analysis For Future Device Cooling Applications, Betty T. Quinton, Levi Elston, James D. Scofield, Sharmila M. Mukhopadhyay
Mechanical and Materials Engineering Faculty Publications
Carbon nanotubes (CNTs) are known for high thermal conductivity and have potential use as nano-radiators or heat exchangers. This paper focuses on the thermal performance of carpet-like arrays of vertically aligned CNTs on solid graphite substrates with the idea of investigating their behavior as a function of carpet dimensions and predicting their performance as thermal interface material (TIM) for electronic device cooling. Vertically aligned CNTs were grown on highly oriented pyrolytic graphite (HOPG) substrate, which creates a robust and durable all-carbon hierarchical structure. The multi-layer thermal analysis approach using Netzsch laser flash analysis system was used to evaluate their performance …
In Situ Defect Detection Using Three Color Spectroscopy In Laser Powder Bed Additive Manufacturing, Andrew Drieling
In Situ Defect Detection Using Three Color Spectroscopy In Laser Powder Bed Additive Manufacturing, Andrew Drieling
The University Honors Program
Additive Manufacturing (AM) provides a way to create parts that would be extremely difficult or impossible with conventional manufacturing processes. However, AM also introduces defects, which are detrimental to the mechanical performance. These defects are potentially unknown until post-processing inspection and testing, wasting time and resources on an unusable part or initiating unexpected failure. Historically, spectroscopy has successfully been used for in situ monitoring of laser welding, using changing parameters in the generated plume to predict defects. In situ monitoring using a visible spectrometer for fabrication of Alloy 718 on a test bed laser powder bed fusion system is performed. …
Distributions Of Pore Sizes And Atomic Densities In Binary Glasses Revealed By Molecular Dynamics Simulations, Nikolai V. Priezjev, Maxim A. Makeev
Distributions Of Pore Sizes And Atomic Densities In Binary Glasses Revealed By Molecular Dynamics Simulations, Nikolai V. Priezjev, Maxim A. Makeev
Mechanical and Materials Engineering Faculty Publications
We report on the results of a molecular dynamics simulation study of porous glassy media, formed in the process of isochoric rapid quenching from a high-temperature liquid state. The transition to a porous solid occurs due to the concurrent processes of phase separation and material solidification. The study is focused on topographies of the model porous structures and their dependence on temperature and average density. To quantify the pore-size distributions, we put forth a scaling relation that provides a satisfactory data collapse in systems with high porosity. We also find that the local density of the solid domains in the …
Wetting Properties Of Structured Interfaces Composed Of Surface-Attached Spherical Nanoparticles, Nikolai V. Priezjev, Bishal Bhattarai
Wetting Properties Of Structured Interfaces Composed Of Surface-Attached Spherical Nanoparticles, Nikolai V. Priezjev, Bishal Bhattarai
Mechanical and Materials Engineering Faculty Publications
The influence of the external pressure and surface energy on the wetting transition at nanotextured interfaces is studied using molecular dynamics and continuum simulations. The surface roughness of the composite interface is introduced via an array of spherical nanoparticles with controlled wettability. We find that in the absence of an external pressure, the liquid interface is flat and its location relative to the solid substrate is determined by the particle size and the local contact angle. With increasing pressure on the liquid film, the interface becomes more curved and the three-phase contact line is displaced along the spherical surface but …
Fabrication And Characterizations Of Lithium Aluminum Titanate Phosphate Solid Electrolytes For Li-Based Batteries, Anurag Yaddanapudi
Fabrication And Characterizations Of Lithium Aluminum Titanate Phosphate Solid Electrolytes For Li-Based Batteries, Anurag Yaddanapudi
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Demands for electric vehicles and flexible electronics have escalated research in developing high-performance lithium batteries based on solid-state chemistry. The present work is to develop highly-conductive and flexible solid electrolyte for such applications. Lithium aluminum titanate phosphate (LATP or Li1.3Al0.3Ti1.7(PO4)3), both in ceramic pellets and free-standing composite membranes, have been fabricated. The crystal structure, surface morphology, and ionic conductivity are systematically studied. LATP pellets are prepared using solid state reaction approach. The results indicate that calcine temperature has significant impacts on the phase impurity and sintering temperature and duration have more impacts on the grain size and porosity of LATP …
Hierarchical Hybrid Architectures For Robust And Reusable Nano-Devices, Sharmila M. Mukhopadhyay
Hierarchical Hybrid Architectures For Robust And Reusable Nano-Devices, Sharmila M. Mukhopadhyay
Mechanical and Materials Engineering Faculty Publications
No abstract provided.
Mechanical Annealing Of Model Glasses: Effects Of Strain Amplitude And Temperature, Nikolai V. Priezjev
Mechanical Annealing Of Model Glasses: Effects Of Strain Amplitude And Temperature, Nikolai V. Priezjev
Mechanical and Materials Engineering Faculty Publications
Molecular dynamics simulations are performed to examine the dynamic response of amorphous solids to oscillatory shear at finite temperatures. The data were collected from a poorly annealed binary glass, which was deformed periodically in the elastic regime during several hundred shear cycles. We found that the characteristic time required to reach a steady state with a minimum potential energy is longer at higher temperatures and larger strain amplitudes. With decreasing strain amplitude, the asymptotic value of the potential energy increases but it remains lower than in quiescent samples. The transient decay of the potential energy correlates well with a gradual …
In Vitro Assessment Of The Effects Of Valvular Stenosis On Aorta Hemodynamics And Left Ventricular Function, Ashish Madan
In Vitro Assessment Of The Effects Of Valvular Stenosis On Aorta Hemodynamics And Left Ventricular Function, Ashish Madan
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Calcific aortic stenosis (CAS) is the most common valvular heart disease and is associated with aortopathy and ventricular dysfunction. Hemodynamic alterations due CAS could affect the aorta lining (endothelium), that is in direct contact with the blood, triggering adverse biological responses that may possibly cause aortic dilation and dissection. Also, CAS could impose excessive ventricular load leading to ventricular wall thickening, thus putting an individual at a higher risk of heart attack or stroke. These pathophysiological effects of CAS are highly dependent on the degree of calcification. However, the impact of CAS development on aorta flow and left ventricular workload …
Influence Of Fdm Build Parameters On Tensile And Compression Behaviors Of 3d Printed Polymer Lattice Structures, Sai Avinash Yadlapati
Influence Of Fdm Build Parameters On Tensile And Compression Behaviors Of 3d Printed Polymer Lattice Structures, Sai Avinash Yadlapati
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This research focuses on the compression and tensile behavior of three-dimensional printed polymer lattice structures with different printing parameters such as build orientation, infill density, and layer thickness. The body-centered cubic (BCC) lattice unit cell, which has been extensively investigated for energy absorption applications, is considered here to create compression and tensile specimens. Special test fixture was designed and developed to perform the tensile tests. The specimens were printed using Acrylonitrile Butadiene Styrene (ABS) polymer material on a Stratasys uPrint 3D printer. The printing parameters considered in this case are: (a) Three different build orientations (0, 45 and 90 degrees); …
Constitutive Modeling Of Creep In Leaded And Lead-Free Solder Alloys Using Constant Strain Rate Tensile Testing, Eric Thomas Stang
Constitutive Modeling Of Creep In Leaded And Lead-Free Solder Alloys Using Constant Strain Rate Tensile Testing, Eric Thomas Stang
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Environmental and safety concerns have necessitated a phase-out of lead-based alloys, which are often used in electronics solder applications. In order to properly assess suitable replacement materials, it is necessary to understand the deformation mechanisms relevant to the application. In the case of electronics solder, creep is an important mechanism that must be considered in the design of reliable devices and systems. In this study, Power-Law and Garofalo constitutive creep models were derived for two medium temperature solder alloys. The first alloy is known by the commercial name Indalloy 236 and is a quaternary alloy of lead, antimony, tin, and …
Design Of A Novel Tissue Culture System To Subject Aortic Tissue To Multidirectional Bicuspid Aortic Valve Wall Shear Stress, Janet Liu
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Blood vessels experience complex hemodynamics marked by three-dimensionality and pulsatility. Arterial endothelial cells interact with the characteristics of the fluid wall shear stress (WSS) to maintain homeostasis or promote disease states. In particular, the bicuspid aortic valve (BAV), a congenital heart valve anatomy consisting of two leaflets instead of three, is associated with aortic complications presumably promoted by hemodynamic abnormalities. While devices have been used to test this hypothesis, their capabilities are limited to the generation of time-varying WSS magnitude in one direction. However, the increased flow helicity generated by BAVs in the aorta is expected to result in increased …
Fabrication And Characterizations Of Lagp/Peo Composite Electrolytes For All Solid-State Lithium-Ion Batteries, Jeremy J. Lee
Fabrication And Characterizations Of Lagp/Peo Composite Electrolytes For All Solid-State Lithium-Ion Batteries, Jeremy J. Lee
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With the rise of electric vehicles and increasing dependence on mobile electronics, the demands for lithium-ion batteries have followed in tandem for their high energy and power densities. However, traditional lithium-ion batteries consisting of liquid electrolytes have limited operating temperatures and are susceptible to ignition and subsequent fires. Recently, battery research has diverged into solid state chemistry to address the aforementioned issues. In this research, we systematically investigate a series of ceramic/polymer lithium-ion conducting composite electrolytes, i.e. Li1.4Al0.4Ge1.6(PO4)3 /lithiated polyethylene oxide (LAGP/PEO). Lithiated PEO was prepared with two different lithium salts, LiBF4 and LITFSI. The impacts of the LAGP on …
Development And Thermal Management Of A Dynamically Efficient, Transient High Energy Pulse System Model, Nathaniel J. Butt
Development And Thermal Management Of A Dynamically Efficient, Transient High Energy Pulse System Model, Nathaniel J. Butt
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As technology advances, the abilities of civilian and military vehicles, both air and ground, will undoubtedly increase as well. One of the main areas of improvement is in the electronics area. The new electronics are ever smaller, use ever higher amounts of electrical power, and require ever smaller temperature tolerances. This leads to the problem of effectively managing the increasing thermal loads and temperature tolerances on these systems. One electronic system that causes concern is a high energy pulse system (HEPS). These devices have very high thermal loads (100s of kW). On an air vehicle, where thermal management by legacy …
Measurement Of Unsteady Characteristics Of Endwall Vortices Using Surface-Mounted Hot-Film Sensors, Emma Michelle Veley
Measurement Of Unsteady Characteristics Of Endwall Vortices Using Surface-Mounted Hot-Film Sensors, Emma Michelle Veley
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High-lift low-pressure turbine blades produce significant losses at the junction with the endwall. The losses are caused by several complex three-dimensional vortical flow structures, which interact with the blade suction surface boundary layer. This study investigates the unsteady characteristics of these endwall flow structures on a highly loaded research profile and the adjacent endwall using surface-mounted hot-film sensors. Experiments were conducted in a low-speed linear cascade wind tunnel. The front-loaded blade profile was subjected to three different inlet conditions, consisting of two turbulence levels, and three incoming boundary layer thicknesses. Multiple surface-mounted hot-film sensors were installed throughout the passage. This …
Design Optimization Of A Non-Axisymmetric Endwall Contour For A High-Lift Low Pressure Turbine Blade, Jacob Allen Dickel
Design Optimization Of A Non-Axisymmetric Endwall Contour For A High-Lift Low Pressure Turbine Blade, Jacob Allen Dickel
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Various approaches have been used to shape the geometry at the junction of the endwall and the blade profile in high-lift low-pressure turbine passages in order to reduce the endwall losses. This thesis will detail the workflow to produce an optimized non-axisymmetric endwall contour design for a front-loaded high-lift research turbine profile. Validation of the workflow was performed and included a baseline planar and test contour case for a future optimization study. Endwall contours were defined using a series of Bezier curves across the passage to create a smooth surface. A parametric based approach was used to develop the test …
Coupling Computational Fluid Dynamics Analysis And Optimization Techniques For Scramjet Engine Design, Nathan T. Mcgillivray
Coupling Computational Fluid Dynamics Analysis And Optimization Techniques For Scramjet Engine Design, Nathan T. Mcgillivray
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Various aspects of hypersonic vehicles are being rapidly explored for improved functionality. One of the main areas of consideration is the fueling of a Supersonic Combusting Ramjet (scramjet) engine. Using Computational Fluid Dynamics (CFD), computer simulations can be performed to analyze the flow physics of a scramjet. In this research, an optimization code, Dakota, is integrated with the CFD to optimize a set of parameters to maximum thrust. In this study, the fuel injection and combustion is replaced with heat sources. This simplification greatly reduces the computational requirements. Additionally, the 3D geometry is reduced to an axisymmetric 2D geometry because …
Identification Of Nonlinear Constitutive Properties Of Damping Coatings, Mackenzie E. Tidball
Identification Of Nonlinear Constitutive Properties Of Damping Coatings, Mackenzie E. Tidball
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Scheduled and unscheduled maintenance actions are a significant cost for gas turbines. Advanced life prediction capabilities help to mitigate these costs. However, the protective thermal and damping coatings applied to the turbine rotors which can help significantly extend component life simultaneously increase the difficulty of modeling the behavior of the components due to the nonlinearity they introduce.This research approaches modeling and analysis of nonlinear coatings for turbine blades and blisks using a nonlinear constitutive law model for the coating. The theoretical frequency response of the nonlinear system is solved for using the harmonic balance method. The coefficients of the nonlinear …
Layer-To-Layer Physical Characteristics And Compression Behavior Of 3d Printed Acrylonitrile Butadiene Styrene Metastructures Fabricated Using Different Process Parameters, Sivani Patibandla
Layer-To-Layer Physical Characteristics And Compression Behavior Of 3d Printed Acrylonitrile Butadiene Styrene Metastructures Fabricated Using Different Process Parameters, Sivani Patibandla
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Three-dimensional (3D) printing, a subset of additive manufacturing, is currently being explored heavily for actual part fabrication due to its ability to create complex objects with intricate internal features. There are several 3D printing technologies; however, the extrusion-based technology such as fused deposition modeling (FDM) is the widely used one owing to its low cost. The FDM method can be used to fabricate parts with different fill densities, fill patterns, and process parameters such as extruder temperature and print speed. In this research, influence of process parameters such as extruder temperature and speed on the physical characteristics such as the …