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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 …
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 …