共查询到20条相似文献,搜索用时 15 毫秒
1.
V. K. Srivastava 《Journal of Materials Science》1986,21(10):3638-3642
Glass fibre-reinforced plastic (GRP) cylinders are increasingly used for highly stressed structural elements. The higher the demands on the materials, the higher are the fault detection requirements to be met by non-destructive materials testing methods. Acousto-ultrasonics is a valuable aid for the non-destructive evaluation of GRP composite materials, because it may be the answer to evaluating effects of subtle defects in composites. The aim of the research is to evaluate the burst pressure of GRP cylinders by acousto-ultrasonics techniques. The theoretical results have been found to be in good agreement with the experimental values. Hence the results strongly suggest that stress wave factor measurements can be exploited successfully to predict burst pressure of GRP cylinders.Nomenclature
P
Internal pressure, kgf cm–2
-
d
Internal diameter, cm
-
t
Thickness of cylinder, cm
- (N
,N
,N
)
Resultant forces, kgf
- (M
,M
,M
)
Moments, kg cm
- [A]
Extensional stiffness matrix
- [B]
Bending stretching coupling matrix
- [D]
Flexural stiffness matrix
- (
0
,
0
,
0
)
Midplane strains
- (k
,k
,k
)
Curvatures
-
n
Number of laminae
-
Z
Distance from midplane, cm
-
u
Ultimate tensile strength of GRP composite, kg cm–2
-
S
W
Stress wave factor
-
m
Material parameter
-
Filament winding angle 相似文献
2.
Meir Weger 《Journal of Low Temperature Physics》1994,95(1-2):131-144
It is generally believed that a high electronic density-of-states n(EF), and therefore a low Fermi velocity vF, are required to obtain a high transition temperature, since Tc ph exp(–1/) and = n(EF)V. However, V = < I2 >/M
ph
2
, and Bardeen showed that I EFkF = (1/2)k
F
2
vF. Thus one may expect that should increase with vF. While it may not be feasable to increase the one-electron velocity vF signifcantly, the velocity may increase greatly as a result of renormalization by electron-electron interactions. Such a renormalization exists in Hartree-Fock theory for an unscreened electron-gas. We found that for a medium-density electron-gas (rs 10–20) imbedded in a background with a dielectric constant () such that / > 10, there is a significant increase of vF by renormalization, even when screening is taken into consideration. The peak of v(k) at k = kF is very narrow, the half width being somewhat less than the frequency 0 at which () falls by a factor of 2. When () is due to ionic polarization, o is a typical phonon frequency. The height of the peak vF/v
F
0
is of order EF/0, and the width in units of momentum is: k/kF (0/EF)2. This velocity peak is associated with a minimum in the screening constant at Ep. Its sharpness causes the normal state properties to be highly anomalous; namely the conductivity is exceptionally high, with an anomalous temperature dependence; the conductivity anisotropy, thermoelectric power, and Hall constant are anomalous. Direct determination of v(k) in YBCO by several methods indeed suggests a large, sharp peak, the width being of order 10 me V. This peak manifests itself in the tunneling and point-contact spectroscopy I–V curves. We suggest that the reduced screening at the Fermi level, associated with this velocity peak, is responsible for the high Tc of the cuprates and several other exotic superconductors. Thus, the high Tc is a reflection of the anomalous normal-state properties. 相似文献
3.
Two kinds of cross-linked urethane methacrylate resins have been investigated using three-point bend tests to determine their environmental stress cracking (ESC) behaviour in a range of liquids (water, sodium hydroxide, ethylene glycol, acetonitrile, acetic acid, acetone, tetrahydrofuran, toluene, 3,5,5-trimethylhexanol and petrol). The resins were found to undergo ESC in organic liquids only, and the critical strains, c, and critical stresses, c, have been related to the solubility parameters, , of the liquid environments. The most severe ESC was observed in solvents with –19–20 MPa1/2, corresponding to minimum points in the plots of c and c against . Generally, the resin with the higher cross-link density had a greater resistance to ESC, but the effect of liquid diffusion complicated the situation and was found to play an important role in the ESC behaviour of these materials. The results confirmed that liquid diffusion into the resins lowered the critical strain (and stress), leading to earlier failure. In the case of the lower cross-link density resin, very fast diffusion was found to cause softening. However, it was noted that liquid diffusion can also blunt crazes and cracks. 相似文献
4.
Superconducting Bi-(Pb)-Sr-Ca-Cu-O ceramics were prepared through the sol-gel method using an aqueous solution of metal acetates containing acetic acid and tartaric acid. The conditions of gelation and conversion of gel to Bi2Sr2CaCu2Ox phase were studied by thermal analysis, infrared absorption spectroscopy and X-ray diffraction technique. It was found that transparent gels were obtained from the solutions containing tartaric acid, with a molar ratio of C4H6O6/Cu of about 0.4. The gel matrix was assumed to be composed of carboxylate anions and metal cations. A gel of molar composition BiSrCaCu = 2223 was decomposed to CaCO3, CaO, CuO and Bi1-x SrxOy (x = 0.2 to 0.3) at low temperatures of 270 to 600 ° C and produced Bi2Sr2CaCu2Ox phase at 800 ° C via complex intermediate states. A rapid cooling of the heated product increasedT
c (end) in the gel of molar composition BiSrCaCu = 2223, while a slow cooling increasedT
c (end) in the lead-containing gel of molar composition BiPbSrCaCu = 1.850.351.92.03.1. The latter showedT
c (onset) at 115 K andT
c (end) at 105K. 相似文献
5.
V. A. Domovtsev 《Journal of Engineering Physics and Thermophysics》1984,47(1):787-790
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
6.
Takekazu Ishida Kiichi Okuda Hidehito Asaoka 《Journal of Low Temperature Physics》1999,117(5-6):1387-1391
Vortex lattice melting in the Hc configuration of an YBa
2
Cu
3
O
6.94
single crystal has been investigated by means of the ac susceptibility – i and the magnetic torque . The melting transition of vortex lattice occurs in Hc, too. Since the torque curve shows a sharp peak in the irreversible torque at
c
90° due to intrinsic pinning at lower temperatures, we can determine the irreversibility line for the intrinsic pinning. The melting transition in the Hc configuration appears at temperatures where the intrinsic-pinning peak is absent. We consider that the intrinsic pinning does not affect the nature of the vortex melting transition in the Hc configuration. 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.
Syozo Imai 《Journal of Low Temperature Physics》1980,40(5-6):595-615
Irradiation of a superconductor by an electromagnetic field with a frequency 0 larger than twice the energy gap (order parameter) decreases the order parameter . We obtain the quasiparticle distribution function n and the dependence of the order parameter on the power of the electromagnetic field P by solving numerically the kinetic equations for n and in the steady state. We take 0/0 = 2.1, 8, and 20, where 0 is the equilibrium value of the order parameter at T = 0 K. In the examples considered the dependence of on the pumping power P becomes double-valued above a critical power. We allow phonons also to be out of thermal equilibrium. To discuss the stability of the steady state thus obtained, we derive kinetic equations for small deviations of the quasiparticle distribution function and the order parameter from the steady state n and by means of the nonequilibrium Green's function theory. Assuming n, exp(i
kr – t), (k) is computed using n
s/, where n
sis the steadystate quasiparticle distribution function for arbitrary . It is concluded in general that the steady state on the upper branch ( >
c
2) is stable with respect to both spatially homogeneous and inhomogeneous fluctuations, and the lower branch ( >
c
2) is unstable;
c
2is the value where the upper and lower branches of (P) coalesce.This work is partly supported by a Grant-in-Aid for Special Project Research from the Ministry of Education, Science and Culture of Japan. 相似文献
9.
The effect of the grain size of the filler on the mechanical properties (compressive, bending, and tensile strength and modulus of elasticity) of synthetic graphite is analyzed using data for commercial structural graphites. As the mean particle size of the filler (av) decreases from 3000 to 1 m, the modulus of elasticity increases, on the average, from 10 to 15 GPa, and the compressive, bending, and tensile strength increases by about one order of magnitude. The Griffith equation is used to evaluate the size of defects that initiate fracture (c
c) in different types of graphites. It is shown that the factors determining the critical defect size depend on the particle size of the filler. For av > 150 m, c
c is comparable to av or max. In the range 30 < av < 150 m, c
c is equal to or greater than max. In graphites with av < 30 m, c
c far exceeds max and, presumably, corresponds to the particle size of the molding powder. 相似文献
10.
A new iterative method for elastic-plastic stress analysis based on a new approximation of the constitutive equations is proposed and compared with standard methods on the accuracy and the computational time in a test problem. The proposed method appears to be better than the conventional methods on the accuracy and comparable with others on the computational time. Also the present method is applied to a crack problem and the results are compared with experimental ones. The agreement of both results are satisfactory.List of symbols
u = (u
1, u
2)
displacements u
(H) = u
(n+1) - u
(n) u
k
(n)
= u
(k
(n + 1)
- u
(n) (n, k = 0, 1, 2, ...)
- = 11, 22, 12)
stresses
- = (11, 22, 12)
strains
- = (11, 22, 12)
center of yield surface
-
D
elastic coeffficient matrix, C = D
–1
-
von Mises yield function. The initial yielding is given by f() =
Y
- f
{f/}
- *
transposed f
-
H
hardening parameter (assumed to be a positive constant for kinematic hardening problems)
-
time derivative of
- [K]
total elastic stiffness matrix
-
T
traction vector
- = [B]
relation between nodal displacements and strains 相似文献
11.
J. B. Sousa M. R. Chaves M. F. Pinheiro R. S. Pinto 《Journal of Low Temperature Physics》1975,18(1-2):125-137
Direct measurements of the temperature derivative of the electrical resistivity d/dT have been made on several ferromagnetic NiCu alloys with high Cu content (20, 30, 40, 50.4 at %). For Ni80Cu20 and Ni70Cu30 the results closely resemble the general pattern found in pure ferromagnets: d/dT - b – a ln ¦¦, for 10–3 ¦¦ 10–1, with a and b constants and = (T/T
c
)– 1. In Ni60Cu40 the rounding off of the magnetic transition is already so pronounced that a similar analysis is hardly significant. In the Ni49.6Cu50.4 sample negative values of d/dT were confirmed above ~165 K. The possible theoretical implications of the results are briefly discussed.Work supported by Instituto de Alta Cultura, Portugal (Project PF1). 相似文献
12.
An investigation was carried out to study the phase transitions in Cu-Ge thin films (80–200 nm in thickness) containing 0, 5, 15, 20, 25, 30, 35, 40, 45 and 50 at% Ge, and the corresponding effects on electrical resistivity. For these films, the phase transitions were found to follow the sequence: -phase (disordered face centred cubic, fcc, solid solution); 5 at% Ge -phase (disordered hexagonal close packed, hcp); 15 at% Ge -phase + 1-phase (ordered orthorhombic, Cu3Ge); 20 at% Ge 1-phase; 25 at% Ge (1-phase + progressively increasing proportions of a disordered Ge-rich solid solution); 30–50 at% Ge. Germanium was found to have no marked effect on grain size of all films studied excluding grain boundaries as electron scattering centres. Transition of the -phase into the -phase was found to occur in a highly coherent manner, which could be related to the reduced stacking fault energy of Cu by the addition of Ge. Most evidence pointed out that the initial increase in resistivity within the -phase range was related to hcp scattering centres, which could be associated with a localized high concentration of Ge. At 15 at% Ge, the resistivity reached a maximum value of about 50 cm associated with the complete transformation of -phase into the -phase. With continued increase in Ge concentration, the resistivity was found to gradually decrease reaching a minimum value of about 10 at 25 at% Ge, which was correlated with complete transition of the -phase into the ordered 1-phase (Cu3Ge). It was shown that the superlattice of Cu3Ge could directly be derived from the disordered -phase by minor atom rearrangement on the [0 0 0 1]hcp plane. Even though, minor proportions of a Ge-rich solid solution containing a small concentration of Cu were formed at Ge concentrations above 25 at%, the minimum resistivity of 10 cm was maintained as the Ge concentration was increased to 35 at%. Subsequently, the resistivity was increased reaching about 46 cm at 50 at% Ge. 相似文献
13.
Study of dielectric and electrical properties of mortar in the early hydration period at microwave frequencies 总被引:1,自引:0,他引:1
X. Z. Ding X. Zhang C. K. Ong B. T. G. Tan J. Yang 《Journal of Materials Science》1996,31(20):5339-5345
The dielectric constant, , and electrical conductivity, , of mortars with various sand-cement ratios,s/c, were measured for the first 30 h hydration using microwave techniques in the frequency range 8.2–12.4 GHz. The and of the mortars were found to increase linearly with increasing water-solid ratiow/(s + c), but decrease with increasings/c. It was found that as long as thes/c values were the same, the rate of changes in and of the mortars were the same. It appears that thes/c is the key factor controlling the rates of changes in dielectric and electrical parameters of cement hydration in mortar. The relationship between compressive strength and dielectric and electrical properties of mortars was also discussed. 相似文献
14.
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
15.
The thermal conductivity, , and the heat capacity per unit volume, c
p
, have been measured for solid silver bromide (AgBr) using the transient hot-wire method. Measurements were made at temperatures in the range 100–400 K and at pressures up to 2 GPa. c
p
was found to be independent of temperature and pressure over these ranges. of AgBr was found to be similar to that of AgCl, which was measured previously. For AgBr, only acoustic phonons needed to be taken into account up to 340 K, but optic phonons probably carried some heat at higher temperatures. The Leibfried-Schlömann (LS) formula could describe the ratio (AgCl)/(AgBr), but not the ratio (1 GPa)/(0) for either substance. An empirical modification of the LS formula could describe the latter ratios but not the former. Further theoretical developments are required for understanding of (P) for even such relatively simple substances as AgCl and AgBr. 相似文献
16.
T. Nagasawa Y. Murata K. Tadano R. Kawai K. Ikehara S. Yano 《Journal of Materials Science》2000,35(12):3077-3082
Dielectric properties and molecular motion were studied by use ofdielectric spectroscopy and differential scanning calorimetry for twoblends, fully transesterificated polyarylate of bisphenol A withterephthalate/isophthalate (50/50) (PA)/polycarbonate of bisphenol A(PC) blends and PA/poly(ethylene terephthalate) (PET) blends. All thequenched PA/PC and PA/PET blends were amorphous and the glasstransition temperature (Tg) was varied with the blends ratioaccording to Gordon-Taylor equation. The PA/PET blends with more than60% of PET crystallized above the crystallization temperature. ThePA/PC and PA/PET blends showed two dielectric relaxations, above Tg and below Tg, which are related to a glasstransition and a local motion of short segment, respectively. The relaxation moved to lower temperatures as PC or PET contentincreases, reflecting the lowering Tg faithfully. In the PA/PETblends, the static (0) and the limiting dielectricconstant (), and the increment () for the relaxation decreases with increasingtemperature and the decrease falled on one curve, independent of theblend ratio. Any ferro- and piezoelectricity were not observed fortwo blends. 相似文献
17.
The interaction between a dislocation and the impurity in KCl: Mg2+ (0.035 mol% in the melt) was investigated at 77–178 K with respect to the two models: one is the Fleischer's model and the other the Fleischer's model taking account of the Friedel relation. The latter is termed the F-F. The dependence of strain-rate sensitivity due to the impurities on temperature for the specimen was appropriate to the Fleischer's model than the F-F. Furthermore, the activation enthalpy, H, for the Fleischer's model appeared to be nearly proportional to the temperature in comparison with the F-F. The Friedel relation between effective stress and average length of the dislocation segments is exact for most weak obstacles to dislocation motion. However, above-mentioned results mean that the Friedel relation is not suitable for the interaction between a dislocation and the impurity in the specimen. Then, the value of H(T
c) at the Fleischer's model was found to be 0.61 eV. H(T
c) corresponds to the activation enthalpy for overcoming of the strain field around the impurity by a dislocation at 0 K. In addition, the Gibbs free energy, G
0, concerning the dislocation motion was determined to be between 0.42 and 0.48 eV on the basis of the following equation ln / = G
0/(kTp0)1 – (T/T
c)1/2
–1(T/T
c)1/2 + ln 0/where k is the Boltzmann's constant, T the temperature, T
c the critical temperature at which the effective stress due to the impurities is zero, p0 the effective shear stress without thermal activation, and 0 the frequency factor. 相似文献
18.
Attenuation of first sound has been measured in 4He under saturated vapor pressure near the lambda temperature T at frequencies /2 ranging from 10.2 to 271 MHz. The frequency dependence of the critical part of the attenuation is determined and the dynamic scaling hypothesis is examined. Above the lambda point, it is found that the critical attenuation is described by a scaling function (, ) = 1+y
F(), where = 0–x
and = T/T – 1, with the results x = 1.02±0.05 and y = 0.33±0.03. The characteristic frequency of the order-parameter fluctuation with the wave number k equal to the inverse correlation length is then proportional to
x
, which is in an excellent agreement with the prediction of dynamic scaling. Below the lambda point, a characteristic relaxation time or times shorter than previously expected at lower frequencies appears to exist in the present frequency range.Based on a Ph.D dissertation submitted by K. Tozaki to the University of Tokyo (1977). 相似文献
19.
We have calculated the attenuation of longitudinal ultrasound due to real order parameter fluctuations in impure polar and planarp-wave superconductors. The quasiparticle self-energy and the corresponding vertex corrections have been included in thet-matrix approximation for arbitrary scattering rate =1/2N and all scattering phase shifts
N (0
N/2). We obtain sound attenuation peaks belowT
c whose heights, positions, and shapes depend on 0 (sound frequency), (0),
N, and (coupling strength due to particle-hole asymmetry). The peaks become much more distinct and sharper for
N
=/2 (resonant scattering by impurities) than for
N=0 (Born approximation). By choosing ,
N, and suitably, qualitative agreement between calculated and observed peaks in UBe13 and UPt3 can be achieved. 相似文献
20.
V. P. Shul'ga 《Strength of Materials》1993,25(3):196-201
A simplified mechanical model of a section of a heat-resistant coating (HRC) as a round plate with an immovable center having radial tangential stresses is presented. It is a natural consequence of a normal density distribution of the probability function for the shear strength and for the local compliance. Stresses and the strength conditions are determined for the two-dimensional case. Also determined is the relationship of to an external thermal load cEc for the one-dimensional case. It was shown that with increase in the value of cEc significant additional (previously unknown) stresses develops in the HRC due to the specifies of the model. Using this model a qualitative explanation of the known experimental data can be given.Translated from Problemy Prochnosti, No. 3, pp. 50–55, March, 1993. 相似文献