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Phase transitions

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Full-Text Articles in Mechanical Engineering

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 Jul 2013

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 strain-induced 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, equal-strength, and stronger high pressure phases, using different scaling parameters in a strain-controlled 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 ...


Strain-Induced Phase Transformations Under Compression, Unloading, And Reloading In A Diamond Anvil Cell, Biao Feng, Oleg M. Zarechnyy, Valery I. Levitas May 2013

Strain-Induced Phase Transformations Under Compression, Unloading, And Reloading In A Diamond Anvil Cell, Biao Feng, Oleg M. Zarechnyy, Valery I. Levitas

Aerospace Engineering Publications

Strain-induced 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 ...


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 Jan 2012

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 large-strain problem on phase transformations (PTs) under compression in a diamond anvil cell is studied in detail using the finite-element method. The combined effect of transformation kinetics and ratios of the yield strengths of low- and high-pressure 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 strain-induced PTs.


Phase-Field Modeling Of Fracture In Liquid, Valery I. Levitas, Alexander V. Idesman, Ameeth K. Palakala Aug 2011

Phase-Field Modeling Of Fracture In Liquid, Valery I. Levitas, Alexander V. Idesman, Ameeth K. Palakala

Aerospace Engineering Publications

Phase-field theory for the description of the overdriven fracture in liquid (cavitation) in tensile pressure wave is developed. Various results from solid mechanics are transferred into mechanics of fluids. Thermodynamic potential is formulated that describes the desired tensile pressure–volumetric strain curve and for which the infinitesimal damage produces infinitesimal change in the equilibrium bulk modulus. It is shown that the gradient of the order parameter should not be included in the energy, in contrast to all known phase-field approaches for any material instability. Analytical analysis of the equations is performed. Problems relevant to the melt-dispersion mechanism of the reaction ...


Phase Transition And Structure Of Silver Azide At High Pressure, Dongbin Hou, Fuxiang Zhang, Cheng Ji, Trevor Hannon, Hongyang Zhu, Jianzhe Wu, Valery I. Levitas, Yanzhang Ma Jul 2011

Phase Transition And Structure Of Silver Azide At High Pressure, Dongbin Hou, Fuxiang Zhang, Cheng Ji, Trevor Hannon, Hongyang Zhu, Jianzhe Wu, Valery I. Levitas, Yanzhang Ma

Aerospace Engineering Publications

ilver azide (AgN 3) was compressed up to 51.3 GPa. The results reveal a reversible second-order orthorhombic-to-tetragonal phase transformation starting from ambient pressure and completing at 2.7 GPa. The phase transition is accompanied by a proximity of cell parameters aand b, a 3° rotation of azide anions, and a change of coordination number from 4-4 (four short, four long) to eight fold. The crystal structure of the high pressure phase is determined to be inI4/mcm space group, with Ag at 4a, N1 at 4d, and N2 at 8h Wyckoff positions. Both of ...