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This is the fifteenth volume of I Physica Status Solidi B i focussed on materials and models showing negative Poisson's ratio (PR), which are often called auxetics, and other systems of unusual, e.g., "negative", characteristics. SP [ sp [1] SP ] sp This time it contains 19 papers which are grouped into three sections. This non-classical effect cannot occur in classical thermo-elasticity but is allowable in Cosserat solids. SP [ sp [17] SP ] sp Next, I Elena Pasternak and Arcady Dyskin i propose a mechanism to control the constriction of elastic rod modulus by lateral compression. This, amongst other things, opens a way to design materials ensuring vibration isolation. SP [ sp [18] SP ] sp I Haifeng Ruan and Dong Li i propose a hierarchical acoustic metamaterial with a spider-web-like structure. [Extracted from the article]

The paper discusses the problem of recovery of the microstructure of the least compliant bodies of non-homogeneous optimal isotropic properties predicted by the Isotropic Material Design method. The three-dimensional microstructure is assumed as constructed by a subsequent lamination process in which two isotropic materials of ordered properties are used, the process being repeated three or six times, subsequently. The Hooke tensors closest to the optimal ones are found by making use of the analytical Francfort--Murat formulae for effective moduli of third and sixth rank sequential laminates. The ability to model an auxetic behavior within the subdomains where the optimal Poisson's ratio assumes negative values is also shown. [ABSTRACT FROM AUTHOR]

We propose in this paper analytical and numerical models that describe the in-plane uniaxial elastic properties (Young's moduli and Poisson's ratios) of a honeycomb structure with curved walls. We perform a parametric analysis of the mechanical performance of this honeycomb also by taking into account the different types of deformations acting inside the cell walls. The curved wall honeycomb possesses higher magnitudes of the Poisson's ratio ν12 in the auxetic configuration compared to classical center symmetric configuration with straight cell wall. The presence of the curvature also allows creating configurations with positive Poisson's ratio even for negative internal cell angles, and makes this honeycomb design attractive for mechanical tailoring. [ABSTRACT FROM AUTHOR]

This paper reports a development of bi-stretch auxetic woven fabrics by using non-auxetic yarns and weaving technology. The fabric structure is first designed based on a re-entrant hexagonal geometry by combination of loose weave and tight weave in a woven fabric structure, and then fabricated on a rapier weaving machine by using both non-elastic and elastic yarns. Two variations of the fabric are produced by using different elastic yarn arrangement in weft direction. The designed auxetic geometry is finally achieved after a washing process due to creation of non-uniform contraction or shrinkage profiles within the fabric structural unit cell. The testing results showed that the developed fabrics exhibit negative Poisson ratio effect in both weft and warp directions in a large range of tensile strain. [ABSTRACT FROM AUTHOR]

This paper reports a new type of auxetic yarn made with circular braiding technology to overcome the yarn slippage problem in the conventional helical auxetic yarn structure. Various auxetic yarn structures are firstly produced on a vertical circular braiding machine with 16 yarn carries by changing the number and arrangement of stiff yarn as well as diameter of elastic yarn and core yarn, and then tested under single and repeating tensile conditions. The results show that not only yarn slippage problem could be overcome in the newly developed auxetic yarn structure, but also an early activation and a higher magnitude of negative Poisson's ratio could be achieved. The results also show that all structural parameters including stiff yarn number and arrangement, core yarn, and elastic yarn diameter have an influence on the auxetic effect of the novel yarn structure. Since the new auxetic yarn is produced by using standard braiding manufacturing technique and conventional non-auxetic yarns, there are few technological barriers for its largescale manufacture for practical application. [ABSTRACT FROM AUTHOR]

In this paper, a novel three-dimensional (3D) cellular structure with negative Poisson's ratio was designed by alternating cuboid surface indents on the vertical ribs of the unit cells. The Poisson's ratio and Young's modulus of structures with different geometric parameters were determined using the finite element method (FEM) as a function of these parameters. Samples with identical geometric variables were fabricated via 3D printing, and their through-thickness direction Poisson's ratios were measured and compared with simulation results. Results showed that the Poisson's ratio of the 3D cellular structures can be tuned from positive to negative and can reach a minimal value of −0.958. Good agreement was found between the experimental results and the simulation. This lattice structure is considerably stiffer than re-entrant negative Poisson's ratio foam with the same solid phase. The design concept developed here can be optimized for specific applications via geometric parameters manipulation. [ABSTRACT FROM AUTHOR]

The structure, elastic properties, and thermodynamic properties of cubic boron arsenide (c‐BAs) under high temperature and high pressure are studied based on first‐principles calculations. The obtained equilibrium structure and mechanical properties are in good agreement with other theoretical results. First, the phonon dispersion spectra at zero pressure and high pressure are calculated. The results show that c‐BAs is dynamically stable under pressure of 0–110 GPa. Second, the lattice constants, elastic constants, Young's modulus, bulk modulus, shear modulus, Poisson's ratio, B/G, sound velocity, and Debye temperature of c‐BAs under zero pressure and high pressure are calculated. c‐BAs are predicted to be unstable above 112.3 GPa in accordance with the elastic stability criterion. Furthermore, it is indicated by the calculated B/G ratio that c‐BAs is brittle at zero GPa and begins to tend to be ductile as pressure rises to 46.4 GPa. The calculated elastic anisotropy coefficients indicate that c‐BAs has elastic anisotropy. The thermodynamic properties of c‐BAs are investigated at high temperatures and pressures by combining generalized density function theory and the quasiharmonic Debye model. It is suggested by the calculated elastic and thermodynamic properties that c‐BAs can be used as candidate structures for the fabrication of efficient solar cells and thermoelectric materials. [ABSTRACT FROM AUTHOR]

Heusler compounds have generated significant interest in spintronics due to their unique features. The structural stability, electronic structure, magnetic, and elastic properties of Heusler alloys VXRh2 (X = Sn, Ge, and Si) are investigated using first‐principles calculations of density functional theory in the Quantum Espresso code. The alloys exhibit three magnetic states (nonmagnetic, ferromagnetic, and ferrimagnetic) and several structural phases (face centered cubic (FCC) and tetragonal). It is found that pressures below 0 GPa produce the FCC phase, while greater pressures produce two tetragonal phases. VSnRh2 is a ferromagnetic metal, while VSiRh2 and VGeRh2 exhibit excellent half‐metallic ferromagnetism. The equilibrium lattice constants of VSiRh2 and VGeRh2 are stable against changes, making these Heusler alloys ideal for spintronic devices. Elastic constant computations show that compounds are mechanically stable. [ABSTRACT FROM AUTHOR]

Monte Carlo simulations in the isobaric-isothermal ensemble with variable shape of the periodic box are used to study elastic properties of two-dimensional (2D) model systems of hard discs with parallel layers of hard cyclic hexamers. Both the particles in their pure phases form elastically isotropic crystals. However, the crystal of discs shows positive and that of hexamers - negative Poisson's ratio (PR). The studied systems with layers are of low symmetry. Hence, a general analytic formula for the orientational dependence of PR in 2D systems is applied to such systems. It is shown that, by changing parameters of the particles and their relative concentration, as well as orientation of the layers, one can obtain systems which are non-auxetic (their PR is positive), auxetic (their PR is negative), or partially auxetic ones (their PR is negative for some directions and positive for other ones). If the disks and hexamers are interpreted as small molecules, the obtained results indicate that by introducing auxetic nano-layers one can strongly modify PR of crystals or even thin layers. The periodic box with N = 224 particles can be thought of as a model of a thin layer or as a model crystalline structure with parallel horizontal layers built of four hard cyclic hexamer rows in the hard disc system. [ABSTRACT FROM AUTHOR]

We describe here a heat-compression protocol used on needle-punched commercial nonwoven fabrics which induces an out-of-plane auxetic response in these treated fabrics. The as-received samples, however, are not auxetic and show a decrease in thickness when stretched uniaxially. Using micro-CT imaging it was found that the vertical fiber bundles/columns, produced in the needle punching step of fabric manufacture, are tilted and buckled as a result of the heat-compression treatment. It is suggested that it is likely the reorientation of these columns during subsequent uniaxial strain that drives thickness increase (auxetic response). Variation of instantaneous Poisson's ratio with axial strain for as-received and treated nonwovens. [ABSTRACT FROM AUTHOR]

Two-dimensional dilational materials, for which the only easy mode of deformation is dilation are reviewed and connections are drawn between models previously proposed in the literature. Some models, which appear to be dilational materials, but which in fact are not, are also discussed. Finally, four new examples of three-dimensional dilational materials are given. [ABSTRACT FROM AUTHOR]

A meshless numerical procedure, known as the method of fundamental solutions, is used to determine elastic deformations of some hypothetical, three-dimensional continua of common or auxetic properties. Demanding boundary conditions, being a mixture of Dirichlet and Neumann ones, are used. The obtained results show very good agreement with those from the standard finite element method. As the applied meshless method is very efficient, it can constitute an interesting alternative to existing methods exploiting various meshes. [ABSTRACT FROM AUTHOR]

Herein, the effects of Cu doping with different concentrations on the stability, elastic properties, and electronic structure of Mg2Si are investigated by first‐principles calculations based on density functional theory. The research results show that Mg2Si and Mg8−xSi4−yCux+y (x, y) = {(0.125, 0), (0, 0.125), (0.25, 0), (0, 0.25), (0.5, 0), (0, 0.5), (1, 0), (0, 1)} are stable in the system. The Cu atoms tend to preoccupy Mg sites in Mg2Si lattices, and the alloying ability is stronger than that of Mg8Si4−yCuy (y = 0.125, 0.25, 0.5, 1). Although all dopants are brittle phases, the doping behavior of Cu atoms improves the elastic and plastic properties of the Mg2Si alloy system. The bonding modes of the crystal are also changed. The SiCu covalent bond formed by Mg8−xSi4Cux (x = 0.125, 0.25, 0.5, 1) further increases the structure stability. Meanwhile, Mg7Si4Cu and Mg8Si3Cu are changed from semiconducting to metallic state by energy band structure analysis. It not only increases the carrier concentration, but also reduces the free electron transition energy, which improves the conductivity of the intrinsic Mg2Si. These investigations will provide some theoretical basis for the application of Mg2Si intermetallic compounds in structural materials and thermoelectric materials. [ABSTRACT FROM AUTHOR]

A stiff tubular cellular structure topology is designed by alternatively indenting rectangular contour patterns on the cell ribs. Modified topologies can be obtained by tailoring the geometric parameters. The Poisson's ratios and elastic moduli of the proposed tubular structures with various geometric parameters are determined using finite element method (FEM). Results show that the minimum Poisson's ratio of the proposed structures can reach −0.28. The unit cell topology and orientation can significantly affect the structures deformation behaviors. The structures exhibit mixed mode of bending‐ and stretching‐dominated deformation responses, and show improved specific elastic moduli compared with traditional open‐cell stochastic foams with positive Poisson's ratios. 3D‐printed samples with identical geometric variables to those of the FE models are fabricated, and their Poisson's ratios and stress–strain relationships are determined experimentally, and compared with simulation results. Excellent agreement is achieved between measurements and simulations. The design concept proposed here can be optimized for specific applications via geometric parameters manipulation. [ABSTRACT FROM AUTHOR]

Chiral materials may exhibit negative Poisson's ratio and deformation‐mode coupling phenomena. The finite element numerical method is adopted to analyze a class of 2D chiral and nonchiral materials and to show the effects of microstructural geometry on their effective elastic properties and coupling between tension/compression and bending. With the same area fraction (AF), nonchiral samples show larger effective moduli than chiral ones. The number of unit cells may reduce negativity in effective Poisson's ratio of the chiral samples due to nonuniform lateral deformation under uniaxial straining. Increasing AF in a hierarchical pattern in the chiral samples makes their Poisson's ratio more negative. Bending occurs in the chiral samples when they are under uniform, uniaxial, tensile, or compressive straining due to the coupling of deformation modes. The sensibility of tension–bending coupling may be controlled by the chiral microstructure. Optimization of the coupling sensitivity may help develop novel mechanical sensors. [ABSTRACT FROM AUTHOR]

Elastic properties and Poisson's ratio of the face centered cubic (fcc) phases of three systems of particles which interact, respectively, through: 1) hard sphere potential (HSP), 2) repulsive Yukawa potential (RYP), and 3) hard‐core repulsive Yukawa potential (HCRYP), studied by Monte Carlo (MC) simulations in the NpT ensemble, are compared in a broad range of pressures between melting and close packing. Partial auxeticity is observed in each of the considered systems and the role of the RYP and HSP, incorporated in HCRYP, is revealed. This study confirms intuitive expectations that the elastic properties of the system with particles interacting through HCRYP at high pressures are well approximated by hard spheres, whereas in the low pressures regime they are close to those obtained for the system with pure Yukawa interactions. It is also demonstrated that in the "transition region", when the HCRYP system is neither close to RYP nor to HSP system, its Poisson's ratio in the directions [110][11¯0] exceeds the ranges given by RYP and HSP for those directions. [ABSTRACT FROM AUTHOR]

Diamond-like structures, that include sp² and sp³ hybridized carbon atoms, are of considerable interest nowadays. In the present work, various carbon auxetic structures are studied by the combination of molecular dynamics (MD) and analytical approach. Two fullerites based on the fullerene C60 and fullerene-like molecule C48 are investigated as well as diamond-like structures based on other fullerene-like molecules (called fulleranes), carbon nanotubes (called tubulanes) and graphene sheets. MD is used to find the equilibrium states of the structures and calculate compliance and stiffness coefficients for stable configurations. Analytical methods are used to calculate the engineering elastic coefficients (Young's modulus, Poisson's ratio, shear modulus and bulk modulus), and to study their transformation under rotation of the coordinate system. All the considered structures are partial auxetics with the negative value of Poisson's ratio for properly chosen tensile directions. It is shown that some of these structures, in a particular tension direction, have a very high Young's modulus, that is, 1852GPa for tubulane TA6. [ABSTRACT FROM AUTHOR]

First principles calculations have been performed to investigate the effects of hydrostatic pressure and biaxial strains (ϵxx) on the electronic and elastic properties of β‐Si3N4. Both bulk modulus and Vickers hardness enhance (decrease) with pressure and compressive (tensile) ϵxx. The evolution of BH/GH ratio indicates that β‐Si3N4 has a better (worse) ductile behavior under pressure and compressive (tensile) ϵxx. The 3D plots of Young's modulus show huge difference in mechanical properties between [0001] direction and a‐b plane and the anisotropy becomes larger by using strain engineering. The sound velocities and Debye temperature are also discussed. The energy gap increases monotonically with pressure, however, strain‐induced changes in band gap are asymmetric and nonlinear. β‐Si3N4 undergoes an indirect to direct band gap transition at biaxial strain of 5%, while β‐Si3N4 is always an indirect band gap semiconductor under pressure and compressive strains. [ABSTRACT FROM AUTHOR]

Soft materials with an embedded stiffer layer are increasingly used in medical and sports engineering. A detailed understanding of the mechanical behavior of such a material system under localised load and resistance to indentation is very important. In this work, the deformation of an isotropic soft matrix with a buried stiffer thin layer under a circular flat indenter was investigated through finite element (FE) modeling. A practical approach in simulating the indentation resistance of such a system (soft matrix with a buried thin stiffer layer) is evaluated. The numerical result is correlated with the data based on analytical approaches for both homogeneous materials and elastic half space with an embedded stiffer layer. The influence of Poisson's ratio and auxeticity of the matrix on the deformation and indentation stiffness of the material system under different conditions (indenter size, sheet thickness, and embedment depth) were established and main influences of the Poisson's ratio on the material deformation and stresses are discussed. The result shows that the influence of matrix auxeticity on indentation resistance is highly depth dependent, with over 30% enhancement of the indentation resistance being predicted for materials with matrix of a negative Poisson's ratio. [ABSTRACT FROM AUTHOR]

Several isotropic two-dimensional crystalline structures are described that exhibit maximum values of the Poisson's ratio at very high pressures. The considered crystals are formed by hard discs of two different diameters which are very close to each other. The investigations of the models are based on Monte Carlo simulations in the isobaric-isothermal ensemble with variable shape of the periodic box. [ABSTRACT FROM AUTHOR]

Microstructured plates, consisting of various conventional and re-entrant cells, are numerically constructed and analyzed for their effective elastic properties under in-plane deformation. The finite element numerical method is adopted. The calculated effective Poisson's ratios of the plates are found to be in the range between −1 and 1, in consistency with the theory of two-dimensional elasticity. Auxetic angles need to be greater than about 20° in order to obtain negative Poisson's ratio. Increasing the auxetic angles reduces the effective pure shear modulus. Elastically anisotropic characteristics of the homogenized plate are analyzed with the calculated effective Young's modulus, Poisson's ratio, and pure shear modulus. [ABSTRACT FROM AUTHOR]

Effective Young's modulus and Poisson's ratios of two-layered cylindrical hollow tubes made of cubic crystals (auxetics and nonauxetics) are considered. An analysis of longitudinal tension of stretching tubes is performed within the framework of curvilinear-anisotropic elasticity and Saint-Venant's approximation. Analytical dependences of effective Young's modulus on the compliance coefficients of the initial crystals and layer thickness as ratio of composites auxetics-nonauxetics are obtained. Deviations from the 'rule of mixtures' predictions which increase with increasing Young's modulus of initial nonauxetics are demonstrated. It is found that effective Poisson's ratios of two-layered tubes depend on the ratio of their thicknesses, the dimensionless combinations of compliance coefficients and a dimensionless radial distance. An effect of tube components on negativeness of effective Poisson's ratio of the composite auxetics-nonauxetics proved to be strongly dependent on the value of Young's modulus for nonauxetic component. It is shown that effective Poisson's ratios for some characteristics of the initial crystals and ratios of layer thicknesses may fall outside the limits on Poisson's ratios of isotropic materials. It is shown that many two-layered tubes composed of pairs of nonauxetics can have large negative effective Poisson's ratios. [ABSTRACT FROM AUTHOR]

We report the high-pressure synthesis and elastic properties of stoichiometric cubic δ-NbN investigated by a combination of experiments and first principles calculations. Using the high pressure solid-state ion-exchange reaction route, we have successfully synthesized polycrystalline δ-NbN at 5.5 GPa and 1673 K. The refined lattice parameter of as-synthesized sample is 4.3960(6) Å, corresponding to the stoichiometric niobium nitride. The determined bulk modulus of δ-NbN is B0 = 319(2) GPa with [ABSTRACT FROM AUTHOR]

Here three analytical models are presented through the layout of wine-rack mechanism in three dimensions (3D) where the conditions for these models to exhibit an extraordinary property, i.e. negative compressibility are specified. In particular, we show that these three models have adjustable compressibility that can be tailored for specific applications and can exhibit NLC, NAC, zero and negative Poisson's ratios in some cases. In this way, the potential of this 2D mechanism in designing 3D models with anomalous properties can be brought out. [ABSTRACT FROM AUTHOR]

It is demonstrated that the large-amplitude, short-wavelength vibrational modes excited in the lattice can change its elastic properties due to physical and/or geometric nonlinearity of the lattice bonds. Depending on the symmetry of the vibrational mode the symmetry of the elastic properties of the lattice can also change. Using as an example the two-dimensional honeycomb structure with β-FPU pairwise interparticle interactions, we demonstrate that the excitation of a large-amplitude vibrational mode in combination with equiaxial tensile strain can change the sign of the Poisson's ratio from positive to negative, thus leading to the auxetic property of the lattice. It is shown that the considered lattice supports discrete breathers, i.e., spatially localized nonlinear vibrational modes. The excitation of the discrete breathers as a result of the modulational instability of the extended short-wavelength modes is analyzed. Our results contribute to the understanding of the relation between the elastic properties and nonlinear dynamics of the lattices of interacting particles. Extended vibrational modes in the 2D honeycomb lattice presented by the stroboscopic pictures of the particle motion. Excitation of such modes with sufficiently large amplitude in combination with equiaxial tension changes the sign of the Poisson's ratio of the lattice from positive to negative. [ABSTRACT FROM AUTHOR]

Elastic properties of the hexagonal crystals under pressure were analyzed. Seven crystals with negative Poisson's ratio (auxetics) were revealed at zero pressure. These are crystals of MoS2, Zn, Be, BeCu (alloy with 2.4 at.% Cu), TiB2, C7H12, and MnAs. Analytical expressions of extreme values of Poisson's ratio and Young's modulus were obtained. For these materials, the variability of Poisson's ratio and Young's modulus was analyzed at pressure change. It was shown that all seven hexagonal auxetics may become completely auxetic under certain pressure values. The variability of the elastic properties of graphite and SiC, being non-auxetics at zero pressure, was considered. These crystals become partially auxetic at negative pressure (-15 GPa for graphite and -56 GPa for silicon carbide) and completely auxetic at -114 and -122 GPa, respectively. The surface of auxeticity v(θ, ψ; p)=0 for hexagonal auxetic MoS2. [ABSTRACT FROM AUTHOR]

Diamond-like carbon nanostructures with cubic anisotropy made by joining fullerene-like molecules of different types via valence bonds are studied by means of molecular dynamics simulations. The considered structures are interesting because they include both sp²- and sp³-hybridized carbon atoms, which lead to their distinct properties compared to the structures with one type of hybridization. Seven diamond-like carbon phases having different shapes of structural units and/or different ways of their connection are studied in the present work. For the relaxed equilibrium structures, the engineering elastic constants (Poisson's ratio,Young's modulus, and shear modulus) are calculated as the functions of the crystal orientation angles. Extreme values of the elastic constants are reported. It is shown that two of the considered diamond-like structures have negative Poisson's ratio and can be regarded as the partial auxetics. According to the results of the present study, elastic properties of the bulk diamond-like carbon structures can vary considerably depending on their structure. [ABSTRACT FROM AUTHOR]

The structural, mechanical, and electronic properties of four orthorhombic noble-metal nitrides TMN2 (TM = Ru, Rh, Os, and Ir) (space group of Pnnm, No: 58) under 100 GPa were investigated through the first-principles calculation using the generalized gradient approximation within the plane-wave pseudopotential density-functional theory. The obtained equilibrium structures are in excellent agreement with other experimental and theoretical results. The calculated formation energy indicates that the nitrides are thermodynamically metastable but mechanically stable at zero pressure. The calculated B/ G ratio indicated RhN2 possesses a ductile nature at 0 GPa, while RuN2, OsN2, and IrN2 are prone to brittleness under pressures of around 20.8, 20.0, and 4.3 GPa, respectively. Then, we calculated the partial and total densities of states. The results show that these four noble-metal nitrides are metallic and the order of metallicity from high to low is: RhN2 > IrN2 > RuN2 > OsN2. Through the charge-density distributions, we find that strong covalency is present in the interstitial dinitrogen units for the four orthorhombic compounds. The calculated hardness of orthorhombic RuN2, RhN2, OsN2, and IrN2 are 13.66, 11.54, 16.33, and 17.92 GPa, respectively. Through the quasiharmonic Debye model, we also investigated the thermodynamic properties of these four compounds. [ABSTRACT FROM AUTHOR]

The structural and elastic properties of the ternary silicides ScTSi (T═Co, Ni, Cu, Ru, Rh, Pd, Ir, Pt) and of the equiatomic intermetallic YTX (T═Ni, Ir; X═Si, Ge, Sn, Pb) are studied using the density-functional theory considering the orthorhombic TiNiSi crystal structure with space group Pnma. From the calculated formation energy, we obtained the following stability order of: ScCuSi < ScCoSi < ScRuSi < ScNiSi < ScPdSi < ScRhSi < ScIrSi < ScPtSi and YNiPb < YNiSn < YNiGe < YNiSi < YIrSn < YIrGe < YIrPb < YIrSi. The lattice parameters and atomic positions are in good agreement with experiments to ∼1%. All the alloys are mechanically stable using the Born elastic stability criteria. Ductile behavior inferred from the Pugh ratio, shear over bulk modulus G/B, and the Cauchy pressure, could be observed only for ScTSi (TRu, Pd, Pt) and YNiSn compounds and moderately for YIrX (Si, Ge, and Sn) and YNiPb. On the contrary, ScTSi (TCo, Ni, Cu, Rh, Ir), YNiGe, and YNiSi compounds are covalent or exhibit G/B > 0.5, leading to a brittle behavior in accordance with the Poisson ratio value. The Zener anisotropy factor is different from 1, indicating that these compounds are elastically anisotropic materials. A strong correlation is found between G and the Young's modulus E, slightly above G ∼(3/8) E widely found for polycrystalline metals. Correlation trend between the Young's modulus E and the shear modulus G of intermetallic compounds. [ABSTRACT FROM AUTHOR]

Abstractauthoren Structural, electronic, elastic, and thermodynamic properties of the spin-gapless semiconducting (SGS) Mn2CoAl inverse Heusler alloy under pressure are investigated by using the density functional theory (DFT) and the quasi-harmonic Debye model. The calculated equilibrium lattice parameter and SGS behavior agree with the experimental and other theoretical data. It is only when the external pressure is beyond about 25 GPa that the SGS behavior and dynamical stability are destroyed, indicating that the SGS behavior is robust against pressure less than 25 GPa in everyday experiments. Furthermore, the thermal properties, including bulk modulus B, thermal expansivity [ABSTRACT FROM AUTHOR]

The thermal expansion [ABSTRACT FROM AUTHOR]

Analytical and numerical features of the elastic properties of curvilinearly anisotropic six-constant tetragonal nano/microtubes are considered. The analytical formulas for Young's modulus and Poisson's ratio are obtained in the case of axial extension. Numerical calculations are performed using these formulas and data on the elastic constants from the Landolt-Börnstein Handbook. The parametric dependences of Young's modulus and Poisson's ratios for nano/microtubes are analyzed in detail. The basic parameters are elastic compliances, chiral angles, and ratios of the radii of hollow cylindrical tubes. [ABSTRACT FROM AUTHOR]

Propagation of infinitely-lived true surface waves (TSW) and of the evanescent surface resonances (pseudo surface waves, PSW) on the inner surface of a cylindrical cavity in an elastic medium coated with a thin elastic membrane is studied. An analogous flat surface with the same coating is considered as a reference system. The dispersion relations of the true surface waves and of the surface resonances are shown to depend on the interplay between the sound speeds in the substrate and in the covering layer. The short-wavelength limit of the excitations in the cavity is checked to be consistent with the case of the flat surface. Analytical expressions are obtained for the cut-offs and for the asymptotic behaviors of the excitations in the long-wavelength and short wavelength limits. The local surface densities of states (LDOS) as well as the real parts of the Green's functions, i.e., analogues of the reactive power, are calculated. The most eminent anomalies of LDOS, which correspond to the longitudinal resonance, are shown to be located close to the apparently spurious roots of the secular determinant of the surface equations of motion. The roots correspond generally to the total conversion of the longitudinal to transverse bulk waves. These roots show cut-offs, where the life time of the longitudinal resonance increases to infinity. For still lower wave vectors the maxima of LDOS follow the lines of total conversion transverse-to-longitudinal with finite life-times. The radius dependence of the cut-off wave vector in the small-radius limit for a fully symmetric torsional mode is [ABSTRACT FROM AUTHOR]

We present the results of an atomistic study on the Poisson's ratios of face-centered cubic metal (001) nanoplates under tensile loading. Here, we find that the behavior of the Poisson's ratios of metal nanoplates is strongly dependent on the characteristics of a phase transformation that takes place in their bulk counterparts as well as on the amount of compressive stress induced in the nanoplates. In addition, we discuss the effects of the nanoplate thickness and temperature on the mechanical behavior of the nanoplates. As the thickness decreases, the amount of compressive stress increases. As a result, the metal nanoplates become more auxetic. Higher temperatures cause the phase transformation to occur sooner. Thus, strongly auxetic nanoplates can be obtained by raising the temperature. In addition to investigating the effects of the thickness and temperature, we compare the behaviors of the Poisson's ratios of (001) nanoplates of six different metals. Interestingly, the behaviors of the Poisson's ratios of the metal nanoplates differ, even though their corresponding bulks have similar and positive Poisson's ratios. This is because the six metals exhibit large differences in their surface stresses as well as in the critical strains for the phase transformation. [ABSTRACT FROM AUTHOR]

We derive the elastic field of a periodic series of straight, inclined, dislocations in a plate using isotropic elasticity for the three components of their common Burgers vector. Explicit expressions are obtained and lead to an easy formulation of spatial derivatives. The displacement field of an isolated dislocation is described asymptotically when the dislocations are distant from each other. A few numerical applications illustrate the stress fields around screw and edge dislocations. In addition, for tungsten, calculations of elastic stored energy give the equilibrium direction of the inclined dislocation as a function of the orientation of its Burgers vector. [ABSTRACT FROM AUTHOR]

The results of first principles calculations of the structural parameters, elastic moduli, electronic structure and optical properties of the ternary rhombohedral layered compounds AEuS2 (A = Na, K, Rb and Cs) are reported. These calculations were performed by employing the Linear Combination of Atomic Orbitals (LCAO) method. The calculated structural parameters using different exchange and correlation approximations are in good agreement with the experimental data, and the best agreement is obtained with the PBE0 functional. The mechanical stability of the AEuS2 compounds is investigated for the first time by calculating the single‐crystal elastic constants Cij using the stress–strain approach; and the macroscopic elastic parameters, such as the bulk modulus β and shear modulus G, were determined by using Voigt–Reuss–Hill approximations (VRH). Electronic properties have been studied through calculation of band structure and density of states. It is shown that these crystals belong to the semiconductors with an indirect band gap. Furthermore, in order to investigate the optical transitions of these compounds, linear optical functions such as the complex dielectric function, optical reflectivity and loss function were computed for an energy range from 0 to 20 eV. The calculated optical spectra show the anisotropic nature of the optical properties of the AEuS2 (A = Na, K, Rb, and Cs) compounds. [ABSTRACT FROM AUTHOR]

First‐principles calculations have been conducted for ɛ‐CL‐20 to study the pressure effects on the structures, elasticity, and sensitivity characteristics under 0–75 GPa. It is found that N–NO2 possesses smaller populations than other bonds and is verified as the trigger bond for ϵ‐CL‐20, and the nitrogen atoms on nitro groups (–NO2) are more sensitive to pressure than that on the rings. A detailed understanding of elasticity has been studied and discussed under pressure. In general, the mechanical properties of ɛ‐CL‐20 are distinctly enhanced under compression. The obtained elastic constants show better agreement with the experiment at zero pressure. As the pressure increases, the lattice interactions towards different directions present pronounced difference. A relationship of C11 ≈ C33 > C22 is obtained in the lower pressure region. However, a different relationship of C11 > C22 ≈ C33 is predicted under higher pressure. The crystal, ɛ‐CL‐20, changes from brittleness to plasticity according to the sharp increase of B/G and C12–C44 under compression. And the band gap of ɛ‐CL‐20 decreases with the increasing pressure, indicating the crystal becomes more sensitive under compression. [ABSTRACT FROM AUTHOR]