共查询到20条相似文献,搜索用时 15 毫秒
1.
We report on a novel extension of the recently introduced phase-field crystal (PFC) method [Elder, Phys. Rev. Lett. 88, 245701 (2002)10.1103/PhysRevLett.88.245701], which incorporates elastic interactions as well as crystal plasticity and diffusive dynamics. In our model, elastic interactions are mediated through wave modes that propagate on time scales many orders of magnitude slower than atomic vibrations but still much faster than diffusive time scales. This allows us to preserve the quintessential advantage of the PFC model: the ability to simulate atomic-scale interactions and dynamics on time scales many orders of magnitude longer than characteristic vibrational time scales. We demonstrate the two different modes of propagation in our model and show that simulations of grain growth and elastoplastic deformation are consistent with the microstructural properties of nanocrystals. 相似文献
2.
A simplified phenomenological theory of the temperature dependence of the second-order elastic constants of crystals is considered.
The temperature dependences of the second-order elastic constants are calculated for a series of cubic crystals with various
types of predominant chemical bonding. Satisfactory agreement between the calculation results and experimental data is obtained.
Fiz. Tverd. Tela (St. Petersburg) 41, 235–240 (February 1999) 相似文献
3.
The paper deals with a detailed numerical study of the sections of the inverse and ray velocity surfaces for cubic crystals.
The figures for the sections of the inverse and ray surfaces by the (001) and (110) planes have been plotted for over 65 crystals
and from these, the nature of the cuspidal edges has been discussed. Typical graphs of the inverse and ray surfaces have been
given. The parameters characterising the dimensions of the cusps have been tabulated. It is shown that the A-15 compounds
exhibit very unusual and interesting wave surfaces at temperatures below superconducting critical temperatures. 相似文献
4.
The models of new isotropic cubic crystals of single-layered carbon nanotubes are proposed. The structural, elastic, and electronic properties and the energies of formation of these crystals were calculated using the density functional-based tight binding (DFTB) method. The crystals proposed were found to exhibit extreme compression moduli (550–650 GPa) and a minimum compressibility (0.0018–0.0015 GPa?1); in this case, the type of conduction of the parent nanotubes was retained. For this reason, the above crystals are of interest for the development of new superhard materials with controllable electrophysical properties. 相似文献
5.
Experimental studies (by the ultrasonic pulse method) and theoretical investigations (with the model of polarizable ions) were made of changes in the elastic moduli of single crystals of NaCl, NaBr, NaI, KCl, KBr, and KI in cubic hydrostatic compression in the pressure range up to 108 Pa at a temperature of 298°K. The experimental unit and method of measurement are described. Theoretical values of the derivatives of the elastic moduli with respect to pressure are presented for the compounds studied and are compared with existing empirical data.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 71–75, October, 1985. 相似文献
6.
W. Maysenhölder 《Physics letters. A》1984,100(6):289-292
The Eshelby factor for cubic crystals has been calculated for arbitrary anisotropy. One of the two integrations needed could be performed analytically. An expansion up to 4th order in the anisotropy and exact results for special cases are also given. 相似文献
7.
J.N. Johnson 《Journal of Physics and Chemistry of Solids》1974,35(5):609-616
When solids are subjected to high-pressure shock-wave loading, multiple stress waves propagate with velocities dependent upon the elastic and inelastic compressibilities of the solid. The present paper shows that the inelastic or plastic waves in cubic and hexagonal single crystals do not necessarily propagate with the bulk sound speed as they do in isotropic elastic-plastic solids. This result is a consequence of anisotropy in the plastic deformation which depends on the slip plane orientation in the crystal and has important consequences with regard to the determination of compressibilities from shock-wave data. In particular, for wave propagation in the <110> directions of cubic crystals the departure from the bulk velocity can be significant (5–25 per cent). For wave propagation normal to the c-axis in hexagonal crystals, the plastic wave velocity also differs from the bulk sound speed (10–25 per cent). Plastic wave velocities are tabulated for a number of cubic crystals on the basis of the various slip systems common to these materials. The calculated velocities are then compared with experimental data on shock-loaded single-crystal aluminum and sodium chloride. 相似文献
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9.
Calculations of mean-square displacements 〈u2〉 of the atoms in adsorbed monolayers on fcc crystals are presented and compared with LEED experimental results. This text is restricted to the case of a C(2 × 2) adsorbed layer on a (100) surface [experimental case of Ni(100) with adsorbed sulfur, sodium, cesium or oxygen]. 〈u2〉's perpendicular to and parallel to a (100) surface are calculated for the adsorbed atoms and the atoms of the first surface layer of the crystal. The values obtained are compared with those for a clean (100) surface and the volume of the crystal. Every possibility for force constants between adsorbate and substrate atoms is examined. It is shown that the measurement of 〈u2〉 perpendicular to the (100) surface yields the adsorbate-substrate force constants and that 〈u2〉 parallel to the (100) surface yields the adsorbate-adsorbate force constants. 相似文献
10.
Planar oscillations of a chain of dumbbell-shaped particles possessing three degrees of freedom are studied. This system models
the dynamics of quasi-one-dimensional crystals consisting of elongated anisotropic molecules. A system of nonlinear differential
equations describing the anharmonic interaction of the elastic and orientational waves in the lattice, corresponding to different
degrees of freedom of the particles, is constructed assuming a cubic interparticle interaction potential. It is shown that
in the low-frequency approximation the system obtained is equivalent to the equations of the moment theory of elasticity,
widely employed for describing nonlinear and dispersion properties of layered crystals and phase transformations in alloys.
Some types of three-wave collinear interactions are investigated, suggesting the possibility of exciting orientational waves
in organic crystals because of their nonlinear interaction with acoustic waves.
Fiz. Tverd. Tela (St. Petersburg) 39, 137–144 (January 1997) 相似文献
11.
12.
Elastic waves in cubic crystals are considered. A new classification of cubic crystals is proposed based on their elastic properties. All cubic crystals are shown to be divided into crystals with a positive or negative anisotropy of their second-order elastic moduli. The vibrational-branch spectra of crystals of these two types differ qualitatively in shape. The angular dependences of the polarization vectors are analyzed. The transverse component in quasi-longitudinal vibrations in cubic crystals is shown to be small and can be neglected. The longitudinal component in quasi-transverse modes is not small: its maximum value is 16.5% for Ge and reaches 27% for KCl. 相似文献
13.
A survey is made of pairs of heteronormal planar elastic waves, which can propagate in an unlimited crystal medium and have equal theoretical values of the phase velocity, using Voigt elastic moduli. Such pairs are chosen for which it is possible that the theoretical equality of velocities will be disturbed when using another theory of the elastic properties of crystals with generally different tensors of material constants (for example Kuvshinskij J. V., Aero E. L.: Fiz. tv. tela5 (1963), 2591). In such a case, a comparison of the measured velocities of a suitable pair of waves can help to decide between the two theories. Pairs of waves are found for 12 non-piezoelectric crystal classes. Among such pairs it is easy to find pairs of waves of the same properties for piezoelectric crystal classes. 相似文献
14.
15.
Decay kinetic properties of a two-level atom near the band edges of photonic crystals (PCs) with absolute gaps are studied based on the Green's function expression for the evolution operator. The local coupling strength between the photons and an atom is evaluated by an exact numerical method. It is found that the decay behavior of an excited atom can be fundamentally changed by the variation of the atomic position: Weisskopf-Wigner and non-Weisskopf-Wigner decay phenomena occur at different atomic positions in the PCs as a result of a significant difference in the local coupling strength. Our finding implies that it is possible to engineer the luminescence spectrum by controlling the atomic position. 相似文献
16.
17.
A statistical approach including direct correlation functions is applied to study the influence of the surface confining the
nematic liquid phase on the Franck elastic coefficients. Specific calculations are made for a model system composed of ellipsoidal
molecules interacting by means of the Gay-Berne potential near the interacting surface.
Fiz. Tverd. Tela (St. Petersburg) 40, 1356–1359 (July 1998) 相似文献
18.
A. I. Smirnov 《Russian Physics Journal》1970,13(9):1227-1229
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20.
The role of elastic stress in statistical and scaling properties of elastic turbulence in a polymer solution flow between two disks is discussed. The analogy with a small-scale magnetodynamics and a passive scalar turbulent advection in the Batchelor regime is used to explain the experimentally observed statistical properties, the flow structure, and the scaling of elastic turbulence. The emergence of a new length scale, namely, the boundary layer thickness, is observed and studied. 相似文献