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31.
The relaxor based ferroelectric (1-x)Pb(Zn(1/3)Nb(2/3))O(3)-xPbTiO(3) and (1-x)Pb(Mg(1/3)Nb(2/3))O(3)-xPbTiO(3) single crystals provided new challenges in property characterization because their extraordinarily large piezoelectric coefficients and electromechanical coupling coefficients. Large errors may occur in some of the derived material constants using conventional characterization techniques. This paper will analyze the inadequacy of the traditional characterization methods and provide some basic guidelines for properly characterizing piezoelectric materials with extremely high piezoelectric and electromechanical coupling coefficients. 相似文献
32.
Indentation Load Effect on Young's Modulus and Hardness of Porous Sialon Ceramic by Depth Sensing Indentation Tests
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Osman SAHIN 《中国物理快报》2007,24(11):3206-3209
Depth sensing indentation (DSI) tests at the range of 200-1800mN are performed on porous sialon ceramic to determine the indentation load on Young's modulus and hardness values. The Young modulus and hardness (Dynamic and Martens) values are deduced by analysing the unloading segments of the DSI test load-displacement curves using the Oliver-Pharr method. It is found that Young's modulus ET, the dynamic hardness HD and the Martens hardness HM exhibit significant indentation load dependences. The values of Young's modulus and hardness decrease with the increasing indentation load, as a result of indentation load effect. The experimental hf /hm ratios lower than the critical value 0.7, with hm being the maximum penetration depth during loading and hf the final unloading depth, indicate that our sample shows the work hardening behaviour. 相似文献
33.
Aditya M. Vora 《Journal of Physics and Chemistry of Solids》2007,68(9):1725-1729
The computations of the static and vibrational properties of four equiatomic Na-based binary alloys viz. Na0.5Li0.5, Na0.5K0.5, Na0.5Rb0.5 and Na0.5Cs0.5, to second order in local model potential is discussed in terms of real-space sum of Born von Karman central force constants. The local field correlation functions due to Hartree (H), Ichimaru-Utsumi (IU) and Sarkar et al. (S) are used to investigate the influence of the screening effects on the aforesaid properties. Results for the lattice constants C11, C12, C44, C12-C44, C12/C44 and bulk modulus B obtained using the H-local field correction function have higher values in comparison with the results obtained for the same properties using IU- and S-local field correction functions. The results for the Shear modulus (C′), deviation from Cauchy's relation, Poisson's ratio σ, Young modulus Y, propagation velocity of elastic waves, phonon dispersion curves and degree of anisotropy A are highly appreciable for the four equiatomic Na-based binary alloys. 相似文献
34.
The stability of nitrogen-doped zirconia/zirconium oxonitride Zr7O11N2 has been studied at pressures up to 20 GPa and temperatures up to 2273 K using a multi-anvil press and X-ray powder diffraction. Depending on pressure and temperature it was found to decompose into the respective stable oxides and nitrides. Therefore the critical influence of temperature, pressure and consequently mechanical tension on doped materials have been revealed. The transition pressures of some oxidic and nitridic high-pressure modifications have been confirmed. The coefficient of thermal expansion of Zr7O11N2 was determined to α(T)=17.94(20)×10−6 K−1+6.35(14)×10−9 K−2×T. 相似文献
35.
Walter C. P. M. Blondel Bertrand Lehalle Gérard Maurice Xiong Wang Jean-François Stoltz 《Rheologica Acta》2000,39(5):461-468
Cryopreservation is widely used to preserve blood vessels for a while but is controversially suspected to affect the mechanical
behavior of these allografts. The aim of this study was to determine whether differences in the three-dimensional mechanical
behavior exist or not between fresh and cryopreserved arteries. Using a previously developed experimental system, in vitro
inflation tests were performed on twenty segments of human fresh and cryopreserved arteries, in static conditions. Opening
angles were also measured from images of rings in zero-stress state. The initial reference state was chosen as the unloaded
state and tests were performed on specimens stretched at natural “in vivo” length. Mechanical measures calculated are “natural”
(Hencky) strains (finite deformations), “true” (Cauchy) stresses in radial, circumferential, and longitudinal directions as
well as strain energy per unit volume. Tangent moduli are derived from radial and circumferential stress-strain characteristics
using non-linear curve fitting. Values of incremental and pressure-strain elastic parameters, wall stiffness, and compliance
per unit length are also calculated. Results are presented in terms of characteristics of stresses and strains in the three
directions, axial force, tangent moduli vs strains or stresses, and energy per unit volume, for both types of artery, with
reference to transmural pressure. Detailed numerical results are given at mean transmural pressure or in the physiological
range. Significant differences are indicated by statistic Student T-tests. Results obtained show that significant differences
exist between rheological properties of fresh and cryopreserved segments of human artery. Strains, stresses, axial force,
strain energy, and wall stiffness values highlight those differences whereas elastic parameters, compliance, and opening angle
do not. The usefulness of some parameters to compare the mechanical behavior existing between fresh and cryopreserved arteries
is therefore underlined.
Received: 3 January 2000 Revision received: 12 April 2000 Accepted: 8 May 2000 相似文献
36.
Markus Clemens Moritz HeliasThorsten Steinmetz Georg Wimmer 《Journal of Computational and Applied Mathematics》2008
The simulation of slowly varying transient electric high-voltage fields and magnetic fields requires the repeated and successive solution of high-dimensional linear algebraic systems of equations with identical or near-identical system matrices and different right-hand side vectors. For these solution processes which are required within implicit time integration schemes and nonlinear (quasi-)Newton–Raphson methods an iterative multiple right-hand side (mrhs) scheme is used which recycles vector subspaces resulting from previous preconditioned conjugate gradient iteration runs. The combination of this scheme with a subspace projection extrapolation start value generation scheme is discussed. Numerical results for three-dimensional electric and magnetic field simulations are presented and the efficiency of the new schemes re-using eigenvector information from previous iteration processes with different tolerance criteria are compared to those of standard conjugate gradient iterations. 相似文献
37.
Zhenhai Liu Stanisaw Migrski Anna Ochal 《Journal of Mathematical Analysis and Applications》2008,340(2):1347-1361
In this paper we consider a mathematical model describing static elastic contact problems with the Hooke constitutive law and subdifferential boundary conditions. We treat boundary hemivariational inequalities which are weak formulations of contact problems. We establish existence and uniqueness of solutions to hemivariational inequalities. Using the notion of H-convergence of elasticity tensors we investigate the limit behavior of the sequence of solutions to hemivariational inequalities. 相似文献
38.
Yuri A. Serebrennikov 《Physics letters. A》2008,372(7):1106-1108
The interplay between spin-orbit interaction in semiconductor valence bands and an adiabatic rotational distortion of the wave function of a charge carrier leads to the scalar spin-orbit-rotation term in the effective-mass Hamiltonian of the conduction-band electron. The physical origin of this result lies in the fact that, similarly to magnetic field effects, the motion of a particle and the phase of its wave function may be affected by the vector potential of the inertial Coriolis field. Here we present a straightforward derivation of this interaction within the multiband envelope function approximation. 相似文献
39.
Within the collective coordinate approach to chiral soliton models we suggest that breaking of SU(3) flavor symmetry mainly resides in the baryon wave-functions while the charge operators maintain a symmetric structure. Sizable symmetry breaking in the wave-functions is required to reproduce the observed spacing in the spectrum of the
baryons. The matrix elements of the flavor symmetric charge operators nevertheless yield gA/gV ratios for hyperon beta-decay which agree with the empirical data approximately as well as the successful F&D parameterization of the Cabibbo scheme. Demanding the strangeness component in the nucleon to vanish in the two flavor limit of the model, determines the structure of the singlet axial charge operator and yields the various quark flavor components of the axial charge of the Λ-hyperon. The suggested picture gains support from calculations in a realistic model using pion and vector meson degrees of freedom to build up the soliton. 相似文献
40.
We have shown that the non-Abelian spin-orbit gauge field strength of the Rashba and Dresselhaus interactions, when split into two Abelian field strengths, the Hamiltonian of the system can be re-expressed as a Landau level problem with a particular relation between the two coupling parameters. The quantum levels are created with up and down spins with opposite chirality and leads to the quantum spin Hall effect. 相似文献