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1.
The Bethany iron meteorite which is a part of the Gibeon shower is a fine octahedrite with zoned plessite fields of various sizes. The optically irresolvable microstructural details inside the plessitic fields have been studied by transmission electron microscopy, and the crystallographic relationships between the primary kamacite () and the parent taenite (), and between the and particles in the coarse plessite, have been examined using electron diffraction. In the case of primary kamacite the orientation-relationship with was close to the Nishiyama-Wasserman relationship, whereas, for the plessitic , the orientation-relationship with was close to Kurdjumov-Sachs. It was also found that the (111) and (110) planes were not strictly parallel. Additionally, measurements of the composition profile through the zoned plessite have been made using STEM microanalysis technique, and related to microstructure.  相似文献   

2.
Summary The response of a solidly rotating liquid bridge consisting of inviscid liquid is determined for pitch excitation about its undisturbed center of mass. Free liquid surface displacement and velocity distribution has been determined in the elliptic (>20) and hyperbolic (<20) excitation frequency range.List of symbols a radius of liquid column - h length of column - I 1 modified Besselfunction of first kind and first order - J 1 Besselfunction of first kind and first order - r, ,z cylindrical coordinates - t time - u, v, w velocity distribution in radial-, circumferential-and axial direction resp. - mass density of liquid - free surface displacement - velocity potential - 0 rotational excitation angle - 0 velocity of spin - forcing frequency - 1n natural frequency - surface tension - acceleration potential - for elliptic range >20 - for hyperbolic range >20  相似文献   

3.
We present data on the copper isotope effect (63Cu-65Cu), Cu =-nTc/nmCu, for two isotopic pairs of oxygen-deficient YBa2Cu3O7–, where varies between 0.06 and 0.52. Cu is below 0.01 at =0.06 (fully oxygenated), it takes values between –0.14 and –0.34 in the 60 K plateau. Larger negative values of Cu are observed away from the plateau. The dependence of Cu is similar to that of the pressure effect dnTc/dP.  相似文献   

4.
The dielectric properties of chemically vapour-deposited (CVD) amorphous and crystalline Si3N4 were measured in the temperature range from room temperature to 800° C. The a.c. conductivity ( a.c.) of the amorphous CVD-Si3N4 was found to be less than that of the crystalline CVD-Si3N4 below 500° C, but became greater than that of the crystalline CVD-Si3N4 over 500° C due to the contribution of d.c. conductivity ( d.c.). The measured loss factor () and dielectric constant () of the amorphous CVD-Si3N4 are smaller than those of the crystalline CVD-Si3N4 in all of the temperature and frequency ranges examined. The relationships of n-1, (- ) n-1 and/(- ) = cot (n/2) (were observed for the amorphous and crystalline specimens, where is angular frequency andn is a constant. The values ofn of amorphous and crystalline CVD-Si3N4 were 0.8 to 0.9 and 0.6 to 0.8, respectively. These results may indicate that the a.c. conduction observed for both of the above specimens is caused by hopping carriers. The values of loss tangent (tan) increased with increasing temperature. The relationship of log (tan) T was observed. The value of tan for the amorphous CVD-Si3N4 was smaller than that of the crystalline CVD-Si3N4.  相似文献   

5.
Sub-parallel concentric conic fractures can be produced consecutively in Perspex by liquid indentation. There is a linear relationshp between the conic angle, , of Hertzian fracture and the Poisson's ratio, , of the material. This angle is about 10 higher than the calculated path of the principal stress trajectory for a given . decreases with the increase of stress application rate. This dependence of is very marked in materials with high Poisson's ratios.  相似文献   

6.
A method is proposed for the joint determination of the coefficients of horizontal particle diffusion and external heat exchange in a stagnant fluidized bed.Notation cf, cs, cn specific heat capacities of gas, particles, and nozzle material, respectively, at constant pressure - D effective coefficient of particle diffusion horizontally (coefficient of horizontal thermal diffusivity of the bed) - d equivalent particle diameter - dt tube diameter - H0, H heights of bed at gas filtration velocities u0 and u, respectively - Ha height of active section - l width of bed - L tube length - l o width of heating chamber - N number of partition intervals - p=H/H0 expansion of bed - sn surface area of nozzle per unit volume of bed - Sh, Sv horizontal and vertical spacings between tubes - tc, t0, ts, tn, tw initial temperature of heating chamber, entrance temperature of gas, particle temperature, nozzle temperature, and temperature of apparatus walls, respectively - u0, u velocity of start of fluidization and gas filtration velocity - y horizontal coordinate - *, coefficient of external heat exchange between bed and walls of apparatus and nozzle - 1, 1, 2, ... coefficients in (4) - thickness of tube wall - b bubble concentration in bed - 0 porosity of emulsion phase of bed - n porosity of nozzle - =(ts – t0)/(tc – t0) dimensionless relative temperature of particles - n coefficient of thermal conductivity of nozzle material - f, s, n densities of gas, particles, and nozzle material, respectively - be=s(1 – 0) (1 – b) average density of bed - time - max time of onset of temperature maximum at a selected point of the bed - R =l o/l Fourier number - Pe = 1 l 2/D Péclet number - Bi = /n Biot number Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 41, No. 3, pp. 457–464, September, 1981.  相似文献   

7.
The field dependence of real () and imaginary () component of ac susceptibility of superconductors within the critical state model can conveniently be used for evaluating the critical current when field amplitude is larger than the penetration field. A method to analyze the real () and imaginary () component of fundamental ac susceptibility with the objective of extracting the temperature dependence of critical current density J c(T) is reported. The procedure makes use of the ac susceptibility data of two polycrystalline (Bi-Pb)-2223 samples measured with different excitation amplitudes below and close to the critical temperature. The temperature dependence of J c is extracted using the isothermal scan over and data. Results obtained from this procedure are found to be in fair agreement with J c(T) calculated from traditional loss-maximum data.  相似文献   

8.
Summary The tangent modulus tensor, denoted as , plays a central role in finite element simulation of nonlinear applications such as metalforming. Using Kronecker product notation, compact expressions for have been derived in Refs. [1]–[3] for hyperelastic materials with reference to the Lagrangian configuration. In the current investigation, the corresponding expression is derived for materials experiencing finite strain due to plastic flow, starting from yield and flow relations referred to the current configuration. Issues posed by the decomposition into elastic and plastic strains and by the objective stress flux are addressed. Associated and non-associated models are accommodated, as is plastic incompressibility. A constitutive inequality with uniqueness implications is formulated which extends the condition for stability in the small to finite strain. Modifications of are presented which accommodate kinematic hardening. As an illustration, is presented for finite torsion of a shaft, comprised of a steel described by a von Mises yield function with isotropic hardening.Notation B strain displacement matrix - C=F T F Green strain tensor - compliance matrix - D=(L+L T )/2 deformation rate tensor - D fourth order tangent modulus tensor - tangent modulus tensor (second order) - d VEC(D) - e VEC() - E Eulerian pseudostrain - F, F e ,F p Helmholtz free energy - F=x/X deformation gradient tensor - f consistent force vector - residual function - G strain displacement matrix - h history vector - h time interval - H function arising in tangent modulus tensor - I, I 9 identity tensor - i VEC(I) - k 0,k 1 parameters of yield function - K g geometric stiffness matrix - K T tangent stiffness matrix - k k kinematic hardening coefficient - J Jacobian matrix - L=v/x velocity gradient tensor - m unit normal vector to yield surface - M strain-displacement matrix - N shape function matrix - n unit normal vector to deformed surface - n 0 unit normal vector to undeformed surface - n unit normal vector to potential surface - r, R, R 0 radial coordinate - s VEC() - S deformed surface - S 0 undeformed surface - t time - t, t 0 traction - t VEC() - VEC( ) - t VEC() - t r reference stress interior to the yield surface - t t–t r - T kinematic hardening modulus matrix - u=x–X displacement vector - U permutation matrix - v=x/t particle velocity - V deformed volume - V 0 undeformed volume - X position vector of a given particle in the undeformed configuration - x(X,t) position vector in the deformed configuration - z, Z axial coordinate - vector of nodal displacements - =(F T F–I)/2 Lagrangian strain tensor - history parameter scalar - , azimuthal coordinate - elastic bulk modulus - flow rule coefficient - twisting rate coefficient - elastic shear modulus - iterate - Second Piola-Kirchhoff stress - Cauchy stress - Truesdell stress flux - deviatoric Cauchy stress - Y, Y yield function - residual function - plastic potential - X, Xe, Xp second order tangent modulus tensors in current configuration - X, Xe, Xp second order tangent modulus tensors in undeformed configuration - (.) variational operator - VEC(.) vectorization operator - TEN(.) Kronecker operator - tr(.) trace - Kronecker product  相似文献   

9.
A new method to measure the thermal diffusivity of liquids is presented. It requires determination of the time dependence of the thermal expansion of the liquid when it is subjected to a heat source at the top of the cell containing the liquid. The high accuracy of the method (about 3%) is due to an essential reduction of convective currents and also to the absence of temperature detectors, which generally introduce unwanted perturbations on the thermal Field.Nomenclature Thermal conductivity - c Specific heat - Density - c = specific heat x density - h Newton coefficient - Thermal diffusivity - T, 0 Temperature - tV Electric signal - Calibration coefficient - exp, th Volume change of the liquid  相似文献   

10.
Some electrical properties of hot-pressed lithium sialons, Li x/8Si6–3x/4Al5x/8O x N8–x havingx<5 and an yttrium sialon were measured between 291 and 775 K; the former consisted essentially of a single crystalline phase whereas the latter contained 98% glassy phase. For lithium sialons, the charging and discharging current followed al(t) t –nlaw withn=0.8 at room temperature. The d.c. conductivities were about 10–13 ohm–1 cm–1 at 291 K and rose to 5×10–7 ohm–1 cm–1 at 775 K. At high temperatures electrode polarization effects were observed in d.c. measurements. The variation of the conductivity over the frequency range 200 Hz to 9.3 GHz followed the () n law. The data also fitted the Universal dielectric law,() n–1 well, and approximately fitted the Kramers-Kronig relation()/()– =cot (n/2) withn decreasing from 0.95 at 291 K to 0.4 at 775 K. The temperature variations of conductivities did not fit linearly in Arrhenius plots. Very similar behaviour was observed for yttrium sialon except that no electrode polarization was observed. The results have been compared with those obtained previously for pure sialon; the most striking feature revealed being that d.c. for lithium sialon can be at least 103 times higher than that of pure sialon. Interpretation of the data in terms of hopping conduction suggests that very similar processes are involved in all three classes of sialon.  相似文献   

11.
The fatigue behaviour of commercially pure aluminium and of nylon under sequentially varying strain amplitudes is compared with a damage law of the type suggested by Miner. Aluminium obeys such a law for both cyclic and uniaxial prestrains but the behaviour of nylon is significantly affected by microcracking, which produces a marked effect of loading sequence.Appendix N Number of strain cycles at a given time - N f Value of N at failure - True tensile stress - True stress range for a strain cycled specimen - h Value of at half the life of the specimen - True tensile strain - Total true strain range - p True plastic strain range (= the breadth of the hysteresis loop at = 0) - d True diametral strain range - E Young's modulus - Linear strain hardening rate when tested at a particular value of p - D Damage due to cycling - D p Damage due to prestrain - p Prestrain. C, K, K1, , are constants  相似文献   

12.
The plastic instability approach has been applied to the tensile behaviour of a continuous fibre composite. It is shown that the combination of two components with different strengths and degrees of work-hardening produces a new material with a new degree of work-hardening, which may be determined by the present analysis. Expressions for the elongation at rupture and the strength of a composite have been obtained and the results of the calculation are compared with some experimental data.List of symbols V f volume fraction of fibres in composite - , , true strain of fibre, matrix and composite - s true stress - , , nominal stress on fibre, matrix and composite - *, *, * critical stress of fibre, matrix and composite (ultimate tensile strength) - *, * critical strain of separate fibre and matrix - * critical strain of composite - Q external load - A cross-sectional area - A 0 initial value of area  相似文献   

13.
Using the results of elastic-plastic stress analyses for notched bars, it is shown that a modified form of slip-line field solution can satisfactorily explain the variation of longitudinal stress ahead of notch tips in strain hardening materials.
Résumé En utilisant les résultats d'analyses de contrainte élastoplastique dans le cas de barres entaillées, on montre qu'il est possible d'utiliser une forme simplifiée de solution du champ des lignes de glissement pour expliquer de façon satisfaisante la variation des contraintes longitudinales en avant d'extrémités d'entaille dans des matériaux susceptibles d'un écrouissage.

Nomenclature yy longitudinal tensile stress in the notch tip plastic zone - xx transverse stress in the x-direction - zz transverse stress in the z-direction - k yield stress in shear - 0 yield stress in tension - 0 * strain hardened yield stress (flow stress) - 0/* c flow stress at notch tip - total total strain pl plastic strain l principal strain - 1 c maximum principal strain at notch tip - 1pl plastic strain in they-direction - 1 cp1 E1 pl at notch tip - eff effective plastic strain - c eff eff at notch tip - 0 yield strainC Stress decay constant in the notch tip region - /epl linear strain hardening rate - n strain hardening exponent in power hardening law - 2 flank angle of notch - distance from notch tip - p notch tip radius - k I applied stress intensity for Mode I loading - E Young's modulus - V c crack tip opening displacement  相似文献   

14.
A method is described for measuring the temperature of a non-steady-state gas flow with a thermocouple which is an inertial component of the first order.Notation T*f non-steady-state gas flow temperature - Tt thermosensor temperature - thermal inertia factor of thermosensor - time - C total heat capacity of thermosensor sensitive element - S total heat-exchange surface between sensitive element and flow - heat-liberation coefficient - temperature distribution nonuniformity coefficient in sensitive element - Re, Nu, Pr, Bi, Pd hydromechanical and thermophysical similarity numbers - P* total flow pressure - P static flow pressure - T* total flow temperature - dt sensitive element diameter - w gas flow velocity - flow density - flow viscosity - f flow thermal conductivity - k gas adiabatic constant - R universal gas constant - M Mach number - T thermodynamic flow temperature - o, o and values at T=288°K - A, m, n, p, r coefficients - c heat-liberation coefficient due to colvection - r heat-liberation coefficient due to radiation - b emissivity of sensitive element material - Stefan-Boltzmann constant - Te temperature of walls of environment - c, r, tc thermosensor thermal inertia factors due to convective, radiant, and conductive heat exchange - L length of sensitive element within flow - a thermal diffusivity of sensitive element material - t thermal conductivity of sensitive element material Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 47, No. 1, pp. 59–64, July, 1984.  相似文献   

15.
The mechanical behaviour of Mg-5.1 wt % Zn alloy single crystals was studied in the 4.2 to 300° K temperature range. Quenched crystals have activation energies and volumes best associated with the cutting of small clusters of Zn atoms by dislocations. Fully hardened crystals contain fine 1 and occasional 2 precipitates with an average 1 interparticle spacing of 330 to 660 Å. Strengthening in these crystals is mainly ascribed to the cutting of 1 particles by dislocations. In the overaged condition 1, 2 and equilibrium particles are present and lead to a considerable temperature-dependence unusual for an overaged condition. Analysis of this temperature-dependence suggests that below 77° K the relatively easy cutting of 1 particles by dislocations takes place in addition to the cutting of 2 and particles. Above 77° K the difficult cutting of 2 and particles alone controls the deformation, 1 being more easily cut with the aid of thermal fluctuations.  相似文献   

16.
The critical curve of a transition of the second kind in an antiferromagnetic superconductor (AFS) with nonmagnetic impurities has been studied. The AFS is described by using the mean-field model given by Nass, Levin, and Grest and assuming a one-dimensional electron band. We find that the points on the critical curve satisfy the thermodynamic stability condition for 01/05.04 and 0.49HQ/01.64.Here 1 is the inverse lifetime of a conduction electron for nonmagnetic impurity scattering,H Q is the antiferromagnetic molecular field, 0 is the zero-temperature order parameter of a superconductor in the absence ofH Q and impurities. Further, 1 and HQ denote the values of these quantities for points on the critical curve. For 1/0>5.04 and HQ/0>1.64, the phase transition from the superconducting to the normal state is always of the second kind. Some thermal properties of the system near the critical curve have also been investigated and we find that these depends dramatically on the impurity concentration.  相似文献   

17.
Some general regularities of dispersion of a gas emerging from a nozzle submerged in a liquid are considered. A condition for establishment of the so-called maximum dispersion state is formulated.Notation 0 coefficient of surface tension at the liquidgas boundary - contact angle of wetting of the nozzle material surface by the liquid - pat atmospheric pressure - p air pressure - density of the liquid - g gravitational acceleration - h height of the liquid column - 1, and g dynamic viscosity coefficients of the liquid and gas, respectively - R and r radii of the bubble and nozzle, respectively - Q and F dimensionless criteria - , , , , and undetermined coefficients - ratio of the circumference of a circle to its diameter  相似文献   

18.
A numerical model for layered composite structures based on a geometrical nonlinear shell theory is presented. The kinematic is based on a multi-director theory, thus the in-plane displacements of each layer are described by independent director vectors. Using the isoparametric apporach a finite element formulation for quadrilaterals is developed. Continuity of the interlaminar shear stresses is obtained within the nonlinear solution process. Several examples are presented to illustrate the performance of the developed numerical model.List of symbols reference surface - convected coordinates of the shell middle surface - i coordinate in thickness direction - i h thickness of layer i - Xo position vector of the reference surface - iXo position vector of midsurface of layer i - t k orthonormal basis system in the reference configuration - i a k orthonormal basis system of layer i - iW axial vector - Ro orthonormal tensor in the reference configuration - i R orthonormal tensor of layer i - i Cauchy stress tensor - i P First Piola-Kirchhoff stress tensor - i q vector of interlaminar stresses - i n, i m vector of stress resultants and stress couple resultants - v x components of the normal vector of boundary - i N, i Q, i M stress resultants and stress couple resultants of First Piola-Kirchhoff tensor - stress resultants and stress couple resultants of Second Piola-Kirchhoff tensor - i , i , i strains of layer i - K transformation matrix - uo displacement vector of layer 1 - i local rotational degrees of freedom of layer i  相似文献   

19.
This paper presents results of an investigation of unsteady periodic heat-transfer, carried out on a special experimental facility.Notation ch contact heat-transfer coefficient - q, qst specific and steady heat flux through the contact zone - Pc contact pressure - , f, m thermal conductivities of the materials of the contact pair, the thermally insulating film, and the intercontact medium - re reduced thermal conductivity - t strength limit of the material - h1, h2 heights of contact-surface profile irregularities - hf thickness of the thermally insulating film - relative area of actual contact - contraction coefficient - c/cy duty factor (ratio of contact duration to working cycle duration) - fcy/fo relative frequency (ratio of contact cycle frequency to a fixed frequency) - a thermal diffusivity - tst steady temperature at depth x from the contact surface - k order of harmonic - cyclic frequency - Ac, Bc Fourier series coefficients - ka amplifier gain - yq heat-flux coordinate on the oscillogram - cs constant stub - l absolute distance of separation - intercontact gap at zero load - b, coefficients describing the surface roughness - relative separation of surfaces - thermocouple sensitivity - r specific electrical resistance Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 37, No. 5, pp. 898–904, November, 1979.  相似文献   

20.
Si-Al-O-N ceramics have been prepared by hot-pressing mixtures of Si3N4, AIN and SiO2 (with an addition of 1% MgO) having varying ratios of AIN/SiO2. Microstructural analysis by transmission electron microscopy and Auger electron spectroscopy has demonstrated the progressive increase in grain-boundary silicate glass in pressings prepared from compositions with excess SiO2 to compositions given by the formula Si6–zAlzOzN8–z. This formula represents the simple substitution of Al for Si atoms and O for N atoms in the hexagonalSi3N4 crystal. Microstructures for this balanced composition are essentially single phase, consiting of non-faceted, sub-micron, grains with a grain-boundary segregate layer of glass-forming silicate composition, containing impurity and additive metal ions, which may be detected only by Auger spectroscopy. This microstructure is in contrast with unbalanced compositions which contain faceted grains joined by a glassy silicate phase which is easily detected by electron microscopy. Final microstructural analysis combined with observations of density and phase content with progress of hot-pressing has confirmed the important role of liquid silicate formation and a solution-reprecipitation mechanism for densification. The presence of a 1% MgO additive is shown to accelerate this process, forming a low melting point silicate by reaction with SiO2, assisting the early solution of AIN and the reprecipitation of substituted crystals.  相似文献   

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