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Articles 1  30 of 49
FullText Articles in Mechanical Engineering
An Exact Formulation For ExponentialLogarithmic Transformation Stretches In A Multiphase Phase Field Approach To Martensitic Transformations, Anup Basak, Valery I. Levitas
An Exact Formulation For ExponentialLogarithmic Transformation Stretches In A Multiphase Phase Field Approach To Martensitic Transformations, Anup Basak, Valery I. Levitas
Aerospace Engineering Publications
A general theoretical and computational procedure for dealing with an exponentiallogarithmic kinematic model for transformation stretch tensor in a multiphase phase field approach to stress and temperature induced martensitic transformations with N martensitic variants is developed for transformations between all possible crystal lattices. This kinematic model, where the natural logarithm of transformation stretch tensor is a linear combination of natural logarithm of the Bain tensors, yields isochoric variantvariant transformations for the entire transformation path. Such a condition is plausible and cannot be satisfied by the widely used kinematic model where the transformation stretch tensor is linear in Bain tensors. Earlier ...
Tensorial Stress−Strain Fields And Large Elastoplasticity As Well As Friction In Diamond Anvil Cell Up To 400 Gpa, Valery I. Levitas, Mehdi Kamrani, Biao Feng
Tensorial Stress−Strain Fields And Large Elastoplasticity As Well As Friction In Diamond Anvil Cell Up To 400 Gpa, Valery I. Levitas, Mehdi Kamrani, Biao Feng
Aerospace Engineering Publications
Various phenomena (fracture, phase transformations, and chemical reactions) studied under extreme pressures in diamond anvil cell are strongly affected by fields of all components of stress and plastic strain tensors. However, they could not be measured. Here, we suggest a coupled experimental−theoretical−computational approach that allowed us (using published experimental data) to refine, calibrate, and verify models for elastoplastic behavior and contact friction for tungsten (W) and diamond up to 400 GPa and reconstruct fields of all components of stress and large plastic strain tensors in W and diamond. Despite the generally accepted straininduced anisotropy, strain hardening, and pathdependent ...
Nde InProcess For Metal Parts Fabricated Using Powder Based Additive Manufacturing, Leonard J. Bond, Lucas W. Koester, Hossein Taheri
Nde InProcess For Metal Parts Fabricated Using Powder Based Additive Manufacturing, Leonard J. Bond, Lucas W. Koester, Hossein Taheri
Aerospace Engineering Publications
Ensuring adequate quality for additive manufactured (AM) materials presents unique metrology challenges to the online process measurement and nondestructive evaluation (NDE) communities. AM parts now have complex forms that are not possible using subtractive manufacturing and there are moves for their use in safety criticality components. This paper briefly reviews the status, challenges and metrology opportunities throughout the AM process from powder to finished parts. The primary focus is on new acoustic signatures that have been demonstrated to correlate process parameters with online measurement for monitoring and characterization during the build. Inprocess, quantitative characterization and monitoring of material state is ...
Slip Of Shuffle Screw Dislocations Through Tilt Grain Boundaries In Silicon, Hao Chen, Valery Levitas, Liming Xiong
Slip Of Shuffle Screw Dislocations Through Tilt Grain Boundaries In Silicon, Hao Chen, Valery Levitas, Liming Xiong
Aerospace Engineering Publications
In this paper, molecular dynamics (MD) simulations of the interaction between tilt grain boundaries (GBs) and a shuffle screw dislocation in silicon are performed. Results show that dislocations transmit into the neighboring grain for all GBs in silicon. For Σ3, Σ9 and Σ19 GBs, when a dislocation interacts with a heptagon site, it transmits the GB directly. In contrast, when interacting with a pentagon site, it first cross slips to a plane on the heptagon site and then transmits the GB. The energy barrier is also quantified using the climbing image nudged elastic band (CINEB) method. Results show that Σ3 ...
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 ...
Morphology And Stress Evolution During The Initial Stages Of Intergranular Corrosion Of X70 Steel, Denizhan Yavas, Abdullah Alshehri, Pratyush Mishra, Pranav Shrotriya, Ashraf F. Bastawros, Kurt R. Hebert
Morphology And Stress Evolution During The Initial Stages Of Intergranular Corrosion Of X70 Steel, Denizhan Yavas, Abdullah Alshehri, Pratyush Mishra, Pranav Shrotriya, Ashraf F. Bastawros, Kurt R. Hebert
Aerospace Engineering Publications
Pipeline steels are vulnerable to stress corrosion cracking (SCC) during intergranular corrosion (IGC) at potentials of active dissolution in moderately alkaline carbonatebicarbonate solutions. Morphology evolution accompanying IGC has not been fully described, despite the relevance of the corrosion geometry to crack initiation. The present article reports a characterization of concurrent morphology and mechanical stress development during the initial stages of IGC of X70 steel in sodium bicarbonate solution, in the potential range of high SCC susceptibility. Morphology was revealed by scanning electron microscope examination of cross sections through the IGC layer, and stress evolution was monitored by curvature interferometry. At ...
Resonance Analysis Of A High Temperature Piezoelectric Disc For Sensitivity Characterization, Prathamesh N. Bilgunde, Leonard J. Bond
Resonance Analysis Of A High Temperature Piezoelectric Disc For Sensitivity Characterization, Prathamesh N. Bilgunde, Leonard J. Bond
Aerospace Engineering Publications
Ultrasonic transducers for high temperature (200 °C+) applications are a key enabling technology for advanced nuclear power systems and in a range of chemical and petrochemical industries. Design, fabrication and optimization of such transducers using piezoelectric materials remains a challenge. In this work, experimental databased analysis is performed to investigate the fundamental causal factors for the resonance characteristics of a piezoelectric disc at elevated temperatures. The effect of all ten temperaturedependent piezoelectric constants (ε33, ε11, d33, d31, d15, s11, s12, s13, s33, s44) is studied numerically on both the radial and thickness mode resonances of a piezoelectric disc. A sensitivity ...
Nanoscale Multiphase Phase Field Approach For Stress And TemperatureInduced Martensitic Phase Transformations With Interfacial Stresses At Finite Strains, Anup Basak, Valery I. Levitas
Nanoscale Multiphase Phase Field Approach For Stress And TemperatureInduced Martensitic Phase Transformations With Interfacial Stresses At Finite Strains, Anup Basak, Valery I. Levitas
Aerospace Engineering Publications
A thermodynamically consistent, novel multiphase phase field approach for stress and temperatureinduced martensitic phase transformations at finite strains and with interfacial stresses has been developed. The model considers a single order parameter to describe the austenite↔martensitic transformations, and another N order parameters describing N variants and constrained to a plane in an Ndimensional order parameter space. In the free energy model coexistence of three or more phases at a single material point (multiphase junction), and deviation of each variantvariant transformation path from a straight line have been penalized. Some shortcomings of the existing models are resolved. Three different kinematic ...
Wear Evolution And Stress Distribution Of Single Cbn Superabrasive Grain In HighSpeed Grinding, Jingwei Wang, Tianyu Yu, Wenfeng Ding, Yucan Fu, Ashraf F. Bastawros
Wear Evolution And Stress Distribution Of Single Cbn Superabrasive Grain In HighSpeed Grinding, Jingwei Wang, Tianyu Yu, Wenfeng Ding, Yucan Fu, Ashraf F. Bastawros
Aerospace Engineering Publications
In this study, both finite element analysis (FEA) and experimental observations were used to investigate the single CBN grain wear in highspeed grinding of Inconel 718 superalloy. The wear characteristics for each grinding pass were numerically assessed utilizing the tensile and compressive strength limits of the cutting grain. Additionally, stress distribution within the grain, chip formation and grinding force evolution during multiple passes were investigated. The combined experimental and numerical results show that the CBN grain wear has two major modes: the macro fracture on the grain top surface propagating from the rake surface, and the micro fracture near the ...
Thermodynamically Consistent And ScaleDependent Phase Field Approach For Crack Propagation Allowing For Surface Stresses, Valery I. Levitas, Hossein Jafarzadeh, Gholam Hossein Farrahi, Mahdi Javanbakht
Thermodynamically Consistent And ScaleDependent Phase Field Approach For Crack Propagation Allowing For Surface Stresses, Valery I. Levitas, Hossein Jafarzadeh, Gholam Hossein Farrahi, Mahdi Javanbakht
Aerospace Engineering Publications
A thermodynamicallyconsistent phase field approach for crack propagation which includes the following novel features is presented. (1) Scale dependency was included by relating the length scale to the number of cohesive interatomic planes at the crack tip. Because of this, the developed theory is applicable from the atomistic to the macroscopic scales. (2) The surface stresses (tension) are introduced by employing some geometrical nonlinearities even in small strain theory. They produce multiple contributions to the GinzburgLandau equation for crack propagation. (3) Crack propagation in the region with compressive closing stresses is eliminated by employing a stressstatedependent kinetic coefficient in the ...
PhaseField Approach For Stress And TemperatureInduced Phase Transformations That Satisfies Lattice Instability Conditions. Part 2. Simulations Of Phase Transformations Si I↔↔ Si Ii, Hamed Babaei, Valery I. Levitas
PhaseField Approach For Stress And TemperatureInduced Phase Transformations That Satisfies Lattice Instability Conditions. Part 2. Simulations Of Phase Transformations Si I↔↔ Si Ii, Hamed Babaei, Valery I. Levitas
Aerospace Engineering Publications

A complete system of equations of the advanced phasefield theory for martensitic phase transformations (PTs) under a general stress tensor is presented. Theory includes a fully geometrically nonlinear formulation for the general case of finite elastic and transformational strains as well as anisotropic and different elastic properties of phases. Material parameters are calibrated, in particular, based on the crystal lattice instability conditions from atomistic simulations for martensitic PTs between cubic Si I and tetragonal Si II phases under complex triaxial compressiontension loading. A finite element algorithm and numerical procedure is developed and implemented in the code deal.II. Various 3D ...
Comparison Of Acoustoelastic Lamb Wave Propagation In Stressed Plates For Different Measurement Orientations, Ning Pei, Leonard J. Bond
Comparison Of Acoustoelastic Lamb Wave Propagation In Stressed Plates For Different Measurement Orientations, Ning Pei, Leonard J. Bond
Aerospace Engineering Publications
High order Lamb waves are investigated for the effects of stress on both symmetrical and antisymmetrical modes in an aluminum plate for wave propagation and load parallel. Data are compared with those for the case of load and measurement axis perpendicular. It is the S1 mode which exhibits significantly higher sensitivity to stress than other Lamb modes. For aluminum the use of the S1 mode for stress measurement is found to be about six times more sensitive, than bulk waves, for the loadmeasurement axes parallel case and this compares with about ten times for the case of loadmeasurement axes perpendicular.
Performance And Modeling Of Paired Polishing Process, Tianyu Yu, David Thomas Asplund, Ashraf F. Bastawros, Abhijit Chandra
Performance And Modeling Of Paired Polishing Process, Tianyu Yu, David Thomas Asplund, Ashraf F. Bastawros, Abhijit Chandra
Aerospace Engineering Publications
Paired polishing process (PPP) is a variant of the chemical mechanical polishing process which facilitates defect mitigation via minimization of maximum force as well as effective planarization via profile driven determination of force gradient. The present embodiment of PPP machine employs two polishing wheels, radially spanning the wafer surface on a countergimbaled base. The PPP machine is deployed to experimentally investigate the role of the process parameters on the surface roughness evolution, and the effective material removal rate. Two sets of copper and aluminum blanket layers were polished under a range of applied down force, polishing wheel speed and transverse ...
Multiple Pure Tone Noise Prediction, Fei Han, Anupam Sharma, Umesh Paliath, Chingwei Shieh
Multiple Pure Tone Noise Prediction, Fei Han, Anupam Sharma, Umesh Paliath, Chingwei Shieh
Aerospace Engineering Publications
This paper presents a fully numerical method for predicting multiple pure tones, also known as “Buzzsaw” noise. It consists of three steps that account for noise source generation, nonlinear acoustic propagation with hard as well as lined walls inside the nacelle, and linear acoustic propagation outside the engine. Noise generation is modeled by steady, partannulus computational fluid dynamics (CFD) simulations. A linear superposition algorithm is used to construct fullannulus shock/pressure pattern just upstream of the fan from partannulus CFD results. Nonlinear wave propagation is carried out inside the duct using a pseudotwodimensional solution of Burgers׳ equation. Scattering from nacelle ...
StrainInduced Phase Transformation Under Compression In A Diamond Anvil Cell: Simulations Of A Sample And Gasket, Biao Feng, Valery I. Levitas, Yanzhang Ma
StrainInduced Phase Transformation Under Compression In A Diamond Anvil Cell: Simulations Of A Sample And Gasket, Biao Feng, Valery I. Levitas, Yanzhang Ma
Aerospace Engineering Publications
Combined high pressure phase transformations (PTs) and plastic flow in a sample within a gasket compressed in diamond anvil cell (DAC) are studied for the first time using finite element method. The key point is that phase transformations are modelled as straininduced, which involves a completely different kinetic description than for traditional pressureinduced PTs. The model takes into account, contact sliding with Coulomb and plastic friction at the boundaries between the sample, gasket, and anvil. A comprehensive computational study of the effects of the kinetic parameter, ratio of the yield strengths of high and lowpressure phases and the gasket, sample ...
Unambiguous Gibbs Dividing Surface For Nonequilibrium FiniteWidth Interface: Static Equivalence Approach, Valery I. Levitas
Unambiguous Gibbs Dividing Surface For Nonequilibrium FiniteWidth Interface: Static Equivalence Approach, Valery I. Levitas
Aerospace Engineering Publications
The definition of all properties of the nonequilibrium interface depends on the choice of the position of the dividing surface. However, the definition of its position has been an unsolved problem for more than a century. A missing principle to unambiguously determine the position of the Gibbs’ dividing surface is found: the principle of static equivalence. A sharp interface (dividing surface) is statically equivalent to a nonequilibrium finitewidth interface with distributed tensile stresses if it possesses (a) the same resultant force, equal to the interface energy, and (b) the same moment, which is zero about the interface position. Each of ...
Multiple Twinning And VariantVariant Transformations In Martensite: PhaseField Approach, Valery I. Levitas, Arunabha M. Roy, Dean L. Preston
Multiple Twinning And VariantVariant Transformations In Martensite: PhaseField Approach, Valery I. Levitas, Arunabha M. Roy, Dean L. Preston
Aerospace Engineering Publications
A phasefield theory of transformations between martensitic variants and multiple twinning within martensitic variants is developed for large strains and lattice rotations. It resolves numerous existing problems. The model, which involves just one order parameter for the description of each variantvariant transformation and multiple twinnings within each martensitic variant, allows one to prescribe the twin interface energy and width, and to introduce interface stresses consistent with the sharp interface limit. A finiteelement approach is developed and applied to the solution of a number of examples of twinning and combined austenitemartensite and martensitemartensite phase transformations (PTs) and nanostructure evolution. A similar ...
Prediction Of Aerodynamic Tonal Noise From Open Rotors, Anupam Sharma, HsuanNien Chen
Prediction Of Aerodynamic Tonal Noise From Open Rotors, Anupam Sharma, HsuanNien Chen
Aerospace Engineering Publications
A numerical approach for predicting tonal aerodynamic noise from ‘‘open rotors’’ is presented. ‘‘Open rotor’’ refers to an engine architecture with a pair of counterrotating propellers. Typical noise spectra from an open rotor consist of dominant tones, which arise due to both the steady loading/thickness and the aerodynamic interaction between the two bladerows. The proposed prediction approach utilizes Reynolds Averaged Navier–Stokes (RANS) Computational Fluid Dynamics (CFD) simulations to obtain near field description of the noise sources. The neartofarfield propagation is then carried out by solving the Ffowcs Williams–Hawkings equation. Since the interest of this paper is limited ...
Plastic Flows And Phase Transformations In Materials Under Compression In Diamond Anvil Cell: Effect Of Contact Sliding, Biao Feng, Valery I. Levitas, Oleg M. Zarechnyy
Plastic Flows And Phase Transformations In Materials Under Compression In Diamond Anvil Cell: Effect Of Contact Sliding, Biao Feng, Valery I. Levitas, Oleg M. Zarechnyy
Aerospace Engineering Publications
Modeling of coupled plastic flows and straininduced phase transformations (PTs) under high pressure in a diamond anvil cell is performed with the focus on the effect of the contact sliding between sample and anvils. Finite element software ABAQUS is utilized and a combination of Coulomb friction and plastic friction is considered. Results are obtained for PTs to weaker, equalstrength, and stronger high pressure phases, using different scaling parameters in a straincontrolled kinetic equation, and with various friction coefficients. Compared to the model with cohesion, artificial shear banding near the constant surface is eliminated. Sliding and the reduction in friction coefficient ...
Phase Field Approach To Interaction Of Phase Transformation And Dislocation Evolution, Valery I. Levitas, Mahdi Javanbakht
Phase Field Approach To Interaction Of Phase Transformation And Dislocation Evolution, Valery I. Levitas, Mahdi Javanbakht
Aerospace Engineering Publications
Phase field approach to coupled evolution of martensitic phase transformations (PTs) anddislocation is developed. A fully geometrically nonlinear formulation is utilized. The finite element method procedure is developed and applied to study the hysteretic behavior and propagation of an austenite (A)–martensite (M) interface with incoherency dislocations, the growth and arrest of martensitic plate for temperatureinduced PT, and the evolution of phase and dislocation structures for stressinduced PT. A similar approach can be developed for the interaction of dislocations with twins and diffusive PTs described by CahnHilliard theory.
StrainInduced Phase Transformations Under Compression, Unloading, And Reloading In A Diamond Anvil Cell, Biao Feng, Oleg M. Zarechnyy, Valery I. Levitas
StrainInduced Phase Transformations Under Compression, Unloading, And Reloading In A Diamond Anvil Cell, Biao Feng, Oleg M. Zarechnyy, Valery I. Levitas
Aerospace Engineering Publications
Straininduced phase transformations (PTs) in a sample under compression, unloading, and reloading in a diamond anvil cell are investigated in detail, by applying finite element method. In contrast to previous studies, the kinetic equation includes the pressure range in which both direct and reverse PTs occur simultaneously. Results are compared to the case when “no transformation” region in the pressure range exists instead, for various values of the kinetic parameters and ratios of the yield strengths of low and high pressure phases. Under unloading (which has never been studied before), surprising plastic flow and reverse PT are found, which were ...
Anisotropic Compositional Expansion And Chemical Potential For Amorphous Lithiated Silicon Under Stress Tensor, Valery I. Levitas, Hamed Attariani
Anisotropic Compositional Expansion And Chemical Potential For Amorphous Lithiated Silicon Under Stress Tensor, Valery I. Levitas, Hamed Attariani
Aerospace Engineering Publications
Si is a promising anode material for Liion batteries, since it absorbs large amounts of Li. However, insertion of Li leads to 334% of volumetric expansion, huge stresses, and fracture; it can be suppressed by utilizing nanoscale anode structures. Continuum approaches to stress relaxation in LixSi, based on plasticity theory, are unrealistic, because the yield strength of LixSi is much higher than the generated stresses. Here, we suggest that stress relaxation is due to anisotropic (tensorial) compositional straining that occurs during insertionextraction at any deviatoric stresses. Developed theory describes known experimental and atomistic simulation data. A method to reduce stresses ...
Interface Stress For Nonequilibrium Microstructures In The Phase Field Approach: Exact Analytical Results, Valery I. Levitas
Interface Stress For Nonequilibrium Microstructures In The Phase Field Approach: Exact Analytical Results, Valery I. Levitas
Aerospace Engineering Publications
An exact expression for the temperaturedependent interface stress tensor (tension) and energy is derived within a phase field approach. The key problem, of which part of the thermal energy should contribute to the surface tension, is resolved with the help of an analytical solution for a nonequilibrium interface. Thus, for a propagating interface at any temperature, the interface stress tensor represents biaxial tension with magnitude equal to the temperaturedependent interface energy. Explicit expressions for the distributions of interface stresses are obtained for a nonequilibrium interface and a critical nucleus. The results obtained are applicable for various phase transformations (solidsolid, meltingsolidification ...
Coupled Phase Transformations And Plastic Flows Under Torsion At High Pressure In Rotational Diamond Anvil Cell: Effect Of Contact Sliding, Biao Feng, Valery I. Levitas
Coupled Phase Transformations And Plastic Flows Under Torsion At High Pressure In Rotational Diamond Anvil Cell: Effect Of Contact Sliding, Biao Feng, Valery I. Levitas
Aerospace Engineering Publications
A threedimensional largesliding contact model coupled with straininduced phase transformations (PTs) and plastic flow in a disklike sample under torsion at high pressure in rotational diamond anvil cell (RDAC) is formulated and studied. Coulomb and plastic friction are combined and take into account variable parameters due to PT. Results are obtained for weaker, equalstrength, and stronger high pressure phases, and for three values of the kinetic coefficient in a straincontrolled kinetic equation and friction coefficient. All drawbacks typical of problem with cohesion are overcome, including eliminating meshdependent shear band and artificial plastic zones. Contact sliding intensifies radial plastic flow, which ...
Advanced PhaseField Approach To Dislocation Evolution, Valery I. Levitas, Mahdi Javanbakht
Advanced PhaseField Approach To Dislocation Evolution, Valery I. Levitas, Mahdi Javanbakht
Aerospace Engineering Publications
The phasefield approach to dislocations is conceptually advanced. Large strain formulation is developed. A local thermodynamic potential eliminates stress dependence of the Burgers vector and reproduces the desired local stressstrain curve, as well as the desired, meshindependent, dislocation height for any dislocation orientation. A gradient energy contains an additional term, which excludes localization of dislocation within a height smaller than the prescribed height but does not produce artificial interface energy and dislocation widening. Problems for nucleation and evolution of multiple dislocations along the single and multiple slip systems, and the interaction of dislocations with an austenite (A)martensite (M) interface ...
CrystalCrystal Phase Transformation Via SurfaceInduced Virtual Premelting, Valery I. Levitas, Zhaohui Ren, Yuewu Zeng, Gaorong Han
CrystalCrystal Phase Transformation Via SurfaceInduced Virtual Premelting, Valery I. Levitas, Zhaohui Ren, Yuewu Zeng, Gaorong Han
Aerospace Engineering Publications
A mechanism for crystalcrystal phase transformations (PTs) via surfaceinduced virtual premelting is justified thermodynamically and confirmed experimentally for the PTs in PbTiO_{3} nanofibers. When the thickness of the surface melt (which appears much below the melting temperature, especially for nanoobjects) exceeds the size of the critical product nucleus, nucleation and growth of the product crystal occur. For nanowires, premelting starts near the smallest size, and hydrodynamic flow driven by reduction in the external surface leads to a large change in shape and further promotion of crystalcrystal PT. During the product crystalgrowth stage, virtual melting is observed experimentally within the ...
Reply To “Comment On 'Mechanochemical Continuum Modeling Of Nanovoid Nucleation And Growth In Reacting Nanoparticles'″, Valery I. Levitas, Hamed Attariani
Reply To “Comment On 'Mechanochemical Continuum Modeling Of Nanovoid Nucleation And Growth In Reacting Nanoparticles'″, Valery I. Levitas, Hamed Attariani
Aerospace Engineering Publications
The problem of the mechanisms of void nucleation in nanoparticles and related problem of the stresses and their relaxation in nanoparticles are of signiﬁcant importance and far from being resolved. It is not surprising that there are several approaches with diﬀerent and, in the given case, opposite assumptions. Thus, in ref 1, surface tension is neglected, and volumetric strain due to oxidation is introduced in the oxide shell. It is stated that for linear lattice mismatch α ≥ 0.3 large tensile stresses in a metal core are suﬃcient for void nucleation.
HighDensity Amorphous Phase Of Silicon Carbide Obtained Under Large Plastic Shear And High Pressure, Valery I. Levitas, Yanzhang Ma, Emre Selvi, Jianzhe Wu, John A. Patten
HighDensity Amorphous Phase Of Silicon Carbide Obtained Under Large Plastic Shear And High Pressure, Valery I. Levitas, Yanzhang Ma, Emre Selvi, Jianzhe Wu, John A. Patten
Aerospace Engineering Publications
In situ xray diffraction study of the hexagonal 6H SiC under pressure and shear in rotational diamond anvil cell is performed that reveals phase transformation to the new highdensity amorphous (hda) phase SiC. In contrast to known lowdensity amorphous SiC, hdaSiC is promoted by pressure and unstable under pressure release. The critical combination of pressure ∼30 GPa and rotation of an anvil of 2160° that causes disordering is determined.
Coupled Plastic Flow And Phase Transformation Under Compression Of Materials In A Diamond Anvil Cell: Effects Of Transformation Kinetics And Yield Strength, Oleg M. Zarechnyy, Valery I. Levitas, Yanzhang Ma
Coupled Plastic Flow And Phase Transformation Under Compression Of Materials In A Diamond Anvil Cell: Effects Of Transformation Kinetics And Yield Strength, Oleg M. Zarechnyy, Valery I. Levitas, Yanzhang Ma
Aerospace Engineering Publications
The largestrain problem on phase transformations (PTs) under compression in a diamond anvil cell is studied in detail using the finiteelement method. The combined effect of transformation kinetics and ratios of the yield strengths of low and highpressure phases is examined. Some experimental phenomena (e.g., plateaus in pressure distribution and plasticflow to the center of a sample) are reproduced. Results are applied to interpretation of experimental data and characterization of straininduced PTs.
Mechanochemical Continuum Modeling Of Nanovoid Nucleation And Growth In Reacting Nanoparticles, Valery I. Levitas, Hamed Attariani
Mechanochemical Continuum Modeling Of Nanovoid Nucleation And Growth In Reacting Nanoparticles, Valery I. Levitas, Hamed Attariani
Aerospace Engineering Publications
Hollow nanoparticles (NPs) are produced by void nucleation and growth during chemical reactions. However, there is no proper understanding of nucleation and growth mechanisms and their predictive modeling. Models based on the Kirkendall effect predict the process time, which is larger by orders of magnitude than in experiment. This is why some works propose that a large tensile pressure in the core causes void nucleation. Here, a continuummechanics approach for nucleation and growth of a nanovoid in reacting NPs based on the Kirkendall effect is developed. In contrast to previous approaches, void nucleation and the effects of stresses are treated ...