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Articles 1 - 12 of 12

Full-Text Articles in Physics

Imaging Stress And Magnetism At High Pressures Using A Nanoscale Quantum Sensor, S. Hsieh, P. Bhattacharyya, C. Zu, T. Mittiga, T. J. Smart, F. Machado, B. Kobrin, T. O. Hohn, N. Z. Rui, Mehdi Kamrani, S. Chatterjee, S. Choi, M. Zaletel, V. V. Struzhkin, J. E. Moore, Valery I. Levitas, R. Jeanloz, N. Y. Yao Dec 2018

Imaging Stress And Magnetism At High Pressures Using A Nanoscale Quantum Sensor, S. Hsieh, P. Bhattacharyya, C. Zu, T. Mittiga, T. J. Smart, F. Machado, B. Kobrin, T. O. Hohn, N. Z. Rui, Mehdi Kamrani, S. Chatterjee, S. Choi, M. Zaletel, V. V. Struzhkin, J. E. Moore, Valery I. Levitas, R. Jeanloz, N. Y. Yao

Aerospace Engineering Publications

Pressure alters the physical, chemical and electronic properties of matter. The development of the diamond anvil cell (DAC) enables tabletop experiments to investigate a diverse landscape of high-pressure phenomena ranging from the properties of planetary interiors to transitions between quantum mechanical phases. In this work, we introduce and utilize a novel nanoscale sensing platform, which integrates nitrogen-vacancy (NV) color centers directly into the culet (tip) of diamond anvils. We demonstrate the versatility of this platform by performing diffraction-limited imaging (~600 nm) of both stress fields and magnetism, up to pressures ~30 GPa and for temperatures ranging from 25-340 K. For ...


Impact Ignition And Combustion Of Micron-Scale Aluminum Particles Pre-Stressed With Different Quenching Rates, Kevin J. Hill, Nobumichi Tamura, Valery I. Levitas, Michelle L. Pantoya Sep 2018

Impact Ignition And Combustion Of Micron-Scale Aluminum Particles Pre-Stressed With Different Quenching Rates, Kevin J. Hill, Nobumichi Tamura, Valery I. Levitas, Michelle L. Pantoya

Materials Science and Engineering Publications

Pre-stressing aluminum (Al) particles by annealing and quenching alters dilatational strain and is linked to increased particle reactivity. The quenching rate associated with pre-stressing is a key parameter affecting the final stress state within the Al particle, with faster quenching rates theoretically favoring a higher, more desirable stress state. Micron scale Al particles are annealed to 573 K, then quenched at different rates (i.e., 200 and 900 K/min), mixed with bismuth oxide (Bi2O3), and the Al + Bi2O3 mixtures are examined under low-velocity, drop-weight impact conditions. Both quenching rates showed increased impact ignition sensitivity (i.e., between 83% and ...


Phase Field Study Of Surface-Induced Melting And Solidification From A Nanovoid: Effect Of Dimensionless Width Of Void Surface And Void Size, Anup Basak, Valery I. Levitas May 2018

Phase Field Study Of Surface-Induced Melting And Solidification From A Nanovoid: Effect Of Dimensionless Width Of Void Surface And Void Size, Anup Basak, Valery I. Levitas

Physics and Astronomy Publications

The size effect and the effects of a finite-width surface on barrierless transformations between the solid (S), surface melt (SM), and melt (M) from a spherical nanovoid are studied using a phase field approach. Melting (SM → M and S → M) from the nanovoid occurs at temperatures which are significantly greater than the solid-melt equilibrium temperature θe but well below the critical temperature for solid instability. The relationships between the SM and M temperatures and the ratio of the void surface width and width of the solid-melt interface, Δ⎯⎯⎯, are found for the nanovoids of different sizes. Below a critical ratio ...


Fem Modeling Of Plastic Flow And Strain-Induced Phase Transformation In Bn Under High Pressure And Large Shear In A Rotational Diamond Anvil Cell, Biao Feng, Valery I. Levitas, Wanghui Li Jan 2018

Fem Modeling Of Plastic Flow And Strain-Induced Phase Transformation In Bn Under High Pressure And Large Shear In A Rotational Diamond Anvil Cell, Biao Feng, Valery I. Levitas, Wanghui Li

Aerospace Engineering Publications

Combined three-dimensional plastic flow and strain-induced phase transformation (PT) in boron nitride (BN) under high pressure and large shear in a rotational diamond anvil cell (rotational DAC or RDAC) are investigated. Geometrically nonlinear frameworks including finite elastic, transformational, and plastic deformations and finite element method (FEM) are utilized. Quantitative information is obtained on the evolutions of the stress tensor, plastic strain, volume fraction of phases in the entire sample, and slip-cohesion transitions, all during torsion under a fixed compressive load in RDAC. The effects of the applied compressive stress and the sample radius on PT and plastic flow are discussed ...


An Experimental Study On The Characteristics Of Wind-Driven Surface Water Film Flows By Using A Multi-Transducer Ultrasonic Pulse-Echo Technique, Yang Liu, Wen-Li Chen, Leonard J. Bond, Hui Hu Jan 2017

An Experimental Study On The Characteristics Of Wind-Driven Surface Water Film Flows By Using A Multi-Transducer Ultrasonic Pulse-Echo Technique, Yang Liu, Wen-Li Chen, Leonard J. Bond, Hui Hu

Aerospace Engineering Publications

An experimental study was conducted to investigate the characteristics of surface water film flows driven by boundary layer winds over a test plate in order to elucidate the underlying physics pertinent to dynamic water runback processes over ice accreting surfaces of aircraft wings. A multi-transducer ultrasonic pulse-echo (MTUPE) technique was developed and applied to achieve non-intrusive measurements of water film thickness as a function of time and space to quantify the transient behaviors of wind-driven surface water filmflows. The effects of key controlling parameters, including freestream velocity of the airflow and flow rate of the water film, on the dynamics ...


Triaxial-Stress-Induced Homogeneous Hysteresis-Free First-Order Phase Transformations With Stable Intermediate Phases, Valery I. Levitas, Hao Chen, Liming Xiong Jan 2017

Triaxial-Stress-Induced Homogeneous Hysteresis-Free First-Order Phase Transformations With Stable Intermediate Phases, Valery I. Levitas, Hao Chen, Liming Xiong

Aerospace Engineering Publications

Starting with thermodynamic predictions and following with molecular dynamics simulations, special triaxial compression-tension states were found for which the stresses for the instability of the crystal lattice of silicon (Si) are the same for direct and reverse phase transformations (PTs) between semiconducting Si I and metallic Si II phases. This leads to unique homogeneous and hysteresis-free first-order PTs, for which each intermediate crystal lattice along the transformation path is in indifferent thermodynamic equilibrium and can be arrested and studied by fixing the strain in one direction. By approaching these stress states, a traditional two-phase system continuously transforms to homogenous intermediate ...


Phase Field Simulations Of Plastic Strain-Induced Phase Transformations Under High Pressure And Large Shear, Mahdi Javanbakht, Valery I. Levitas Dec 2016

Phase Field Simulations Of Plastic Strain-Induced Phase Transformations Under High Pressure And Large Shear, Mahdi Javanbakht, Valery I. Levitas

Aerospace Engineering Publications

Pressure and shear strain-induced phase transformations (PTs) in a nanograined bicrystal at the evolving dislocations pile-up have been studied utilizing a phase field approach (PFA). The complete system of PFA equations for coupled martensitic PT, dislocation evolution, and mechanics at large strains is presented and solved using the finite element method (FEM). The nucleation pressure for the high-pressure phase (HPP) under hydrostatic conditions near a single dislocation was determined to be 15.9 GPa. Under shear, a dislocation pile-up that appears in the left grain creates strong stress concentration near its tip and significantly increases the local thermodynamic driving force ...


Phase Field Approach With Anisotropic Interface Energy And Interface Stresses: Large Strain Formulation, Valery I. Levitas, James A. Warren Jun 2016

Phase Field Approach With Anisotropic Interface Energy And Interface Stresses: Large Strain Formulation, Valery I. Levitas, James A. Warren

Aerospace Engineering Publications

A thermodynamically consistent, large-strain, multi-phase field approach (with consequent interface stresses) is generalized for the case with anisotropic interface (gradient) energy (e.g. an energy density that depends both on the magnitude and direction of the gradients in the phase fields). Such a generalization, if done in the “usual” manner, yields a theory that can be shown to be manifestly unphysical. These theories consider the gradient energy as anisotropic in the deformed configuration, and, due to this supposition, several fundamental contradictions arise. First, the Cauchy stress tensor is non-symmetric and, consequently, violates the moment of momentum principle, in essence the ...


Self-Consistent Swept Frequency Eddy Current Measurements For Characterization Of Near Surface Material Conditions, Chester C.H. Lo, Anatoli M. Frishman, Y. Shen, Norio Nakagawa Jul 2008

Self-Consistent Swept Frequency Eddy Current Measurements For Characterization Of Near Surface Material Conditions, Chester C.H. Lo, Anatoli M. Frishman, Y. Shen, Norio Nakagawa

Center for Nondestructive Evaluation Conference Papers, Posters and Presentations

This paper reports on a self‐consistent, swept frequency eddy current (SFEC) technique for characterizing surface and sub‐surface conditions of materials, with specific applications to detecting residual stresses in shot‐peened Ni‐base superalloys and surface oxidation in engineering components. The technique involves measuring lift‐off normalized vertical component signal to suppress lift off noise and instrumentation effect. Theoretical study shows that the vertical component signals are insensitive to coil dimensions, thus enabling EC measurements in separate frequency bands using multiple coils, while yielding continuous broad‐band data so that both the bulk conductivity and near‐surface conductivity profile ...


A Scaling Law For Nondestructive Evaluation Of Shot Peening Induced Surface Material Property Deviations, Anatoli M. Frishman, Chester C.H. Lo, Y. Shen, Norio Nakagawa Jul 2008

A Scaling Law For Nondestructive Evaluation Of Shot Peening Induced Surface Material Property Deviations, Anatoli M. Frishman, Chester C.H. Lo, Y. Shen, Norio Nakagawa

Center for Nondestructive Evaluation Conference Papers, Posters and Presentations

Shot peening is frequently used to improve mechanical characteristics of metallic components’ surfaces. The physical properties of shot peened surfaces exhibit deviations from their bulk values. This paper shows that there exists a scaling law (universality) among seemingly unrelated material property deviations and among different peening conditions. We present examples and support for scaling behaviors based on experimental data on Almen strip deflection, cold work and residual stress profiles of a shot peened nickel‐base superalloy (Waspaloy), and swept frequency eddy current signals used for NDE studies of another shot peened nickel‐base superalloy (Inconel 718). In addition, a fast ...


Shot-Peening Intensities Vs. Eddy Current Signals As Seen In Iterative Treatment-Measurement Experiment, Norio Nakagawa, Anatoli M. Frishman, Y. Shen, Chester C.H. Lo Jul 2008

Shot-Peening Intensities Vs. Eddy Current Signals As Seen In Iterative Treatment-Measurement Experiment, Norio Nakagawa, Anatoli M. Frishman, Y. Shen, Chester C.H. Lo

Center for Nondestructive Evaluation Conference Papers, Posters and Presentations

We report on progress in a swept high frequency eddy current (SHFEC) technique for characterization of surface residual stress on shot‐peened superalloy surfaces. Our aim here is to demonstrate the sensitivity of our measurement for practical shot peening intensities, i.e. at 4 ∼ 6 A. First, we present our improved probe and instrumentation being sufficiently sensitive to resolve the surface conditions at these low Almen intensities, where our earlier measurements encountered noise problems. The previous coil was also larger (18 mm in diameter) than desirable. Our new probe integrates smaller coils (12 mm in diameter, forming an AC bridge ...


Simulation Of Chemical Mechanical Planarization Of Copper With Molecular Dynamics, Y. Ye, Rana Biswas, Ashraf F. Bastawros, Abhijit Chandra Sep 2002

Simulation Of Chemical Mechanical Planarization Of Copper With Molecular Dynamics, Y. Ye, Rana Biswas, Ashraf F. Bastawros, Abhijit Chandra

Aerospace Engineering Publications

With an aim to understanding the fundamental mechanisms underlying chemical mechanical planarization ~CMP! of copper, we simulate the nanoscale polishing of a copper surface with molecular dynamics utilizing the embedded atom method. Mechanical abrasion produces rough planarized surfaces with a large chip in front of the abrasive particle, and dislocations in the bulk of the crystal. The addition of chemical dissolution leads to very smooth planarized copper surfaces and considerably smaller frictional forces that prevent the formation of bulk dislocations. This is a first step towards understanding the interplay between mechanistic material abrasion and chemical dissolution in chemical mechanical planarization ...