Elastic,dielectric, and piezoelectric characterization of 0.92Pb(Zn1/3Nb2/3)O3-0.08PbTiO3 single crystal by Brillouin scattering

In this paper,a complete set of elastic,piezoelectric,and dielectric constants of high-quality tetragonal poled0.92Pb(Zn_(1/3)Nb_(2/3))O_3-0.08PbTiO_3 single crystal grown by the modified flux method is determined using high-resolution Brillouin scattering.A comparison is made between the results obtained by a hybrid method combining ultrasonic and resonant techniques and the results obtained by the Brillouin scattering.The elastic,piezoelectric,and dielectric constants obtained by the two methods are similar.The Brillouin spectrum consists of one longitudinal and two transverse acoustic phonon modes,and the variations of the Brillouin shifts,the full widths at half maximum,and the scattering intensities of these modes with scattering angle 9 are investigated.In particular,the transverse acoustic phonon mode at the lowfrequency becomes markedly soft from 28.2 GHz to 18.4 GHz and broadens gradually with the increase of θ,while its intensity decreases gradually as compared with that of the original one.The possible origins of the results are discussed.     

First-Principles Calculations of Elastic and Thermal Properties of Molybdenum Disilicide

The first-principles plane-wave pseudopotential method using the generalized gradient approximation within the framework of density functional theory is applied to anaylse the equilibrium lattice parameters, six independent elastic constants, bulk moduli, thermal expansions and heat capacities of MoSi2. The quasi-harmonic Debye model, using a set of total energy versus cell volume obtained with the plane-wave pseudopotential method, is applied to the study of the elastic properties, thermodynamic properties and vibrational effects. The calculated zero pressure elastic constants are in overall good agreement with the experimental data. The calculated heat capacities and the thermal expansions agree well with the observed values under ambient conditions and those calculated by others. The results show that the temperature has hardly any effect under high pressure.     

Elastic properties of anatase titanium dioxide nanotubes:A molecular dynamics study

The elastic properties of anatase nanotubes are investigated by molecular dynamics(MD) simulations. Young's modulus, Poisson ratio, and shear modulus are calculated by transversely isotropic structure model. The calculated elastic constants of bulk rutile, anatase, and Young's modulus of nanotube are in good agreement with experimental values, respectively, demonstrating that the Matsui and Akaogi(MA) potential function used in the simulation can accurately present the elastic properties of anatase titanium dioxide nanotubes. For single wall anatase titanium dioxide nanotube, the elastic moduli are shown to be sensitive to structural details such as the chirality and radius. For different chirality nanotubes with the same radius, the elastic constants are not proportional to the chiral angle. The elastic properties of the nanotubes with the chiral angle of 0° are worse than those of other chiral nanotubes. For nanotubes with the same chirality but different radii, the elastic constant, Young's modulus, and shear modulus decrease as the radius increases. But there exist maximal values in a radius range of 10 nm–15 nm. Such information can not only provide a deep understanding of the influence of geometrical structure on nanotubes mechanical properties, but also present important guidance to optimize the composite behavior by using nanotubes as the addition.     

Equation of State and Elastic Constants of Compressed fcc Cu

First-principles calculations of equation of state and single-crystal elastic constants of copper are carried out up to twofold compression. The Helmholtz free energies are calculated using the quasi-harmonic phonon approach based on density-functional theory within both the local density approximation and the generalized gradient approximation （GGA）. We find that the results calculated within GGA agree better with the experimental measurements in overall. The equation of state and the zero-pressure single-crystal elastic constants are close to the experimental values.     

A Calculation Approach to Elastic Constants of Crystallines at High Pressure and Finite Temperature

Elastic constants of Na and Li metals are calculated successfully for temperatures up to 350K and pressures up to 30GPa using a scheme without involving any adjustable parameter.Elastic constants are assumed to depend only on an effective pair potential that is only determined by the average interatomic distance.Temperature has an effect on elastic constants by way of charging the equilibrium.The elastic constants can be obtained by fitting the relationship between total energy and strain tensor using the new set of lattice parameters obtained by calculating displacement of atoms at the finite temperature and at a fixed pressure.The relationship between the effective pair potential and the interatiomic distance is fitted by using a series of data of cohesive energy corresponding to lattice parameters.     

First-principles calculations for the elastic properties of Ni-base model superalloys: Ni/Ni3Al multilayers

A model system consisting of Ni[001](100)/Ni3Al[001](100) multi-layers are studied using the density functional theory in order to explore the elastic properties of single crystal Ni-based superalloys. Simulation results are consistent with the experimental observation that rafted Ni-base superalloys virtually possess a cubic symmetry. The convergence of the elastic properties with respect to the thickness of the multilayers are tested by a series of multilayers from 2γ′+2γ to 10γ′+10γ atomic layers. The elastic properties are found to vary little with the increase of the multilayer’s thickness. A Ni/Ni3Al multilayer with 10γ′+10γ atomic layers (3.54 nm) can be used to simulate the mechanical properties of Ni-base model superalloys. Our calculated elastic constants, bulk modulus, orientation-dependent shear modulus and Young’s modulus, as well as the Zener anisotropy factor are all compatible with the measured results of Ni-base model superalloys R1 and the advanced commercial superalloys TMS-26, CMSX-4 at a low temperature. The mechanical properties as a function of the γ′ phase volume fraction are calculated by varying the proportion of the γ and γ′ phase in the multilayers. Besides, the mechanical properties of two-phase Ni/Ni3Al multilayer can be well predicted by the Voigt-Reuss-Hill rule of mixtures.     

Electronic and Elastic Properties of Helical Nickel Nanowires

The structural and elastic properties of ultrathin nickel nanowires are investigated by using molecular dynamics simulation with a Sutton-Chen potential. Helical multi-shell structures are obtained as the most stable structures for Ni nanowires with diameters of about 1 nm. The electronic states of these nanowires are computed and compared with that of Ni solid. The mechanical responses of the helical nanowires under tensile forces are simulated. We observe elastic deformation of nanowires characterized by periodic oscillations of the nanowire length under constant force. Within an elastic limit, both the atomic structures and the electronic structures remain stable under external tensile loading.     

Elastic and Dynamical Properties of YB4： First-Principles Study

We present the elastic and dynamical properties of YB4 from first-principles calculations. It is found that the optimized lattice constants and bulk modulus （182 GPa） agree well with the experimental data. The structural stability of tetragonal YB4 is confirmed by the calculated elastic constants and phonon spectra. YB4 holds a Debye temperature of 874 K and has small elastic anisotropy. The estimated hardness of YB4 is about 17 GPa, indicating that YB4 is a hard solid while not a superhard one.     

Laser Generation of Surface Waves on Cylinder with a Slow Coating

An analytical model of acoustic field excited by a pulsed-laser line source on a coated cylinder is presented. Surface wave dispersive behaviours for a cylinder with a slow coating are analysed and compared with that of a bare cylinder. Based on this analysis, the laser-generated transient response of the perturbed Rayleigh wave and the higher modes of steel cylinder with a zinc coating are calculated from the model using residue theory and FFT technique. The theoretical result from the superposed waveform of the perturbed Rayleigh wave and higher modes agree well with the waveform obtained in experiment. The results show that the model and numerical method provide a useful technique for quantitatively characterizing coating parameters of coated cylinder by the laser generated surface waves.     

Dynamic Tensile Behavior and Fracture Mechanism of Polymer Composites Embedded with Tetraneedle-Shaped ZnO Nanowhiskers

Dynamic tensile properties of glass-fiber polymer composites embedded with ZnO nanowhiskers are investigated by a split Hopkinson tensile bar. The stress-strain curves, ultimate strength, failure strain and elastic modulus are obtained and the failure mechanism of the composites is investigated by the macroscopic and microscopic observation of fractured specimens. The strain rate effect on the mechanical behavior is discussed and a constitutive model is derived by simulating the experimental data. The experimental results show that the materials have an obvious non-linear constitutive relation and strain rate strengthening effect. The composites with ZnO nanowhiskers under dynamic loading have various failure modes and better mechanical properties.