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Articles 1  12 of 12
FullText Articles in Physics
FatigueResistant HighPerformance Elastocaloric Materials Via Additive Manufacturing, Huilong Hou, Emrah Simsek, Tao Ma, Nathan S. Johnson, Suxin Qian, Cheikh Cissé, Drew Stasak, Naila Al Hasan, Lin Zhou, Yunho Hwang, Reinhard Radermacher, Valery I. Levitas, Matthew J. Kramer, Mohsen Asle Zaeem, Aaron P. Stebner, Ryan T. Ott, Jun Cui, Ichiro Takeuchi
FatigueResistant HighPerformance Elastocaloric Materials Via Additive Manufacturing, Huilong Hou, Emrah Simsek, Tao Ma, Nathan S. Johnson, Suxin Qian, Cheikh Cissé, Drew Stasak, Naila Al Hasan, Lin Zhou, Yunho Hwang, Reinhard Radermacher, Valery I. Levitas, Matthew J. Kramer, Mohsen Asle Zaeem, Aaron P. Stebner, Ryan T. Ott, Jun Cui, Ichiro Takeuchi
Aerospace Engineering Publications
Elastocaloric cooling, which exploits the latent heat released and absorbed as stressinduced phase transformations are reversibly cycled in shape memory alloys, has recently emerged as a frontrunner in nonvaporcompression cooling technologies. The intrinsically high thermodynamic efficiency of elastocaloric materials is limited only by work hysteresis. Here, we report on creating highperformance lowhysteresis elastocaloric cooling materials via additive manufacturing of TitaniumNickel (TiNi) alloys. Contrary to established knowledge of the physical metallurgy of TiNi alloys, intermetallic phases are found to be beneficial to elastocaloric performances when they are combined with the binary TiNi compound in nanocomposite configurations. The resulting microstructure gives rise ...
Kinetics Of The Γ–Δ Phase Transition In Energetic NitramineOctahydro1,3,5,7Tetranitro1,3,5,7Tetrazocine, P. Bowlan, B. F. Henson, L. Smilowitz, Valery I. Levitas, N. Suvorova, D. Oschwald
Kinetics Of The Γ–Δ Phase Transition In Energetic NitramineOctahydro1,3,5,7Tetranitro1,3,5,7Tetrazocine, P. Bowlan, B. F. Henson, L. Smilowitz, Valery I. Levitas, N. Suvorova, D. Oschwald
Aerospace Engineering Publications
The solid, secondary explosive nitramineoctahydro1,3,5,7tetranitro1,3,5,7 or HMX has four different stable polymorphs which have different molecular conformations, crystalline structures, and densities, making structural phase transitions between these nontrivial. Previous studies of the kinetics of the β–δ HMX structural transition found this to happen by a nucleation and growth mechanism, where growth was governed by the heat of fusion, or melting, even though the phase transition temperature is more than 100 K below the melting point. A theory known as virtual melting could easily justify this since the large volume difference in the two ...
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
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 highpressure 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 nitrogenvacancy (NV) color centers directly into the culet (tip) of diamond anvils. We demonstrate the versatility of this platform by performing diffractionlimited imaging (~600 nm) of both stress fields and magnetism, up to pressures ~30 GPa and for temperatures ranging from 25340 K. For ...
Lattice Instability During SolidSolid Structural Transformations Under A General Applied Stress Tensor: Example Of Si I → Si Ii With Metallization, Nikolai A. Zarkevich, Hao Chen, Valery I. Levitas, Duane D. Johnson
Lattice Instability During SolidSolid Structural Transformations Under A General Applied Stress Tensor: Example Of Si I → Si Ii With Metallization, Nikolai A. Zarkevich, Hao Chen, Valery I. Levitas, Duane D. Johnson
Aerospace Engineering Publications
The density functional theory was employed to study the stressstrain behavior and elastic instabilities during the solidsolid phase transformation (PT) when subjected to a general stress tensor, as exemplified for semiconducting Si I and metallic Si II, where metallization precedes the PT, so stressed Si I can be a metal. The hydrostatic PT occurs at 76 GPa, while under uniaxial loading it is 11 GPa (3.7 GPa mean pressure), 21 times lower. The Si I → Si II PT is described by a critical value of the phasefield’s modified transformation work, and the PT criterion has only two parameters ...
Fem Modeling Of Plastic Flow And StrainInduced Phase Transformation In Bn Under High Pressure And Large Shear In A Rotational Diamond Anvil Cell, Biao Feng, Valery I. Levitas, Wanghui Li
Fem Modeling Of Plastic Flow And StrainInduced 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 threedimensional plastic flow and straininduced 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 slipcohesion 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 ...
Phase Transitions And Their Interaction With Dislocations In Silicon, Valery I. Levitas, Hao Chen, Liming Xiong
Phase Transitions And Their Interaction With Dislocations In Silicon, Valery I. Levitas, Hao Chen, Liming Xiong
Aerospace Engineering Publications
In this paper, phase transformations (PTs) in silicon were investigated through molecular dynamics (MD) using Tersoff potential. In the first step, simulations of PTs in single crystal silicon under various stresscontrolled loading were carried out. Results shows that all instability points under various stress states are described by criteria, which are linear in the space of normal stresses. There is a region in the stress space in which conditions for direct and reverse PTs coincide and a unique homogeneous phase transition (without nucleation) can be realized. Finally, phase transition in bicrystalline silicon with a dislocation pileup along the grain boundary ...
High Pressure Phase Transformations Revisited, Valery I. Levitas
High Pressure Phase Transformations Revisited, Valery I. Levitas
Aerospace Engineering Publications
High pressure phase transformations play an important role in the search for new materials and material synthesis, as well as in geophysics. However, they are poorly characterized, and phase transformation pressure and pressure hysteresis vary drastically in experiments of different researchers, with different pressure transmitting media, and with different material suppliers. Here we review the current state, challenges in studying phase transformations under high pressure, and the possible ways in overcoming the challenges. This field is critically compared with fields of phase transformations under normal pressure in steels and shape memory alloys, as well as plastic deformation of materials. The ...
TriaxialStressInduced Homogeneous HysteresisFree FirstOrder Phase Transformations With Stable Intermediate Phases, Valery I. Levitas, Hao Chen, Liming Xiong
TriaxialStressInduced Homogeneous HysteresisFree FirstOrder 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 compressiontension 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 hysteresisfree firstorder 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 twophase system continuously transforms to homogenous intermediate ...
An Experimental Study On The Characteristics Of WindDriven Surface Water Film Flows By Using A MultiTransducer Ultrasonic PulseEcho Technique, Yang Liu, WenLi Chen, Leonard J. Bond, Hui Hu
An Experimental Study On The Characteristics Of WindDriven Surface Water Film Flows By Using A MultiTransducer Ultrasonic PulseEcho Technique, Yang Liu, WenLi 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 multitransducer ultrasonic pulseecho (MTUPE) technique was developed and applied to achieve nonintrusive measurements of water film thickness as a function of time and space to quantify the transient behaviors of winddriven 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 ...
Phase Field Simulations Of Plastic StrainInduced Phase Transformations Under High Pressure And Large Shear, Mahdi Javanbakht, Valery I. Levitas
Phase Field Simulations Of Plastic StrainInduced Phase Transformations Under High Pressure And Large Shear, Mahdi Javanbakht, Valery I. Levitas
Aerospace Engineering Publications
Pressure and shear straininduced phase transformations (PTs) in a nanograined bicrystal at the evolving dislocations pileup 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 highpressure phase (HPP) under hydrostatic conditions near a single dislocation was determined to be 15.9 GPa. Under shear, a dislocation pileup 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
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, largestrain, multiphase 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 nonsymmetric and, consequently, violates the moment of momentum principle, in essence the ...
Simulation Of Chemical Mechanical Planarization Of Copper With Molecular Dynamics, Y. Ye, Rana Biswas, Ashraf F. Bastawros, Abhijit Chandra
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 ...