共查询到20条相似文献,搜索用时 672 毫秒
1.
Kyu Hyun Kyung Hyun Ahn Seung Jong Lee Masataka Sugimoto Kiyohito Koyama 《Rheologica Acta》2006,46(1):123-129
In this study, linear and branched polypropylenes (PP) were compared under medium strain amplitude oscillatory shear (usually
strain amplitude range from 10 to 100%) with Fourier-transform rheology (FT rheology). On a log–log diagram, the third relative
intensity (I
3/I
1), which is a parameter to represent nonlinearity, shows a linear relationship with the strain amplitude in the range of medium
strain amplitude. The slope of I
3/I
1 of linear PP with various molecular weight and molecular weight distribution was 2 as most constitutive equations predict,
while that of branched PP was 1.64, which is lower than that of linear PP. When the linear and branch PP were blended, the
slope of I
3/I
1 was proportional to the composition of the branch PP. Therefore, it is suggested that the degree of branching can be defined
in terms of the slope of I
3/I
1 under medium amplitude oscillatory shear. 相似文献
2.
DOUBLEHIGHORDERS-BREAKINGBIFURCATIONPOINTSANDTHEIRNUMERICALDETERMINATION¥(杨忠华,叶瑞松)YangZhonghua;(DepartmentofMathematics,Shangh... 相似文献
3.
Anisotropy of Seismic Attenuation in Fractured Media: Theory and Ultrasonic Experiment 总被引:1,自引:0,他引:1
This is a study on anisotropy of seismic attenuation in a transversely isotropic (TI) model, which is a long-wavelength equivalent
of an isotropic medium with embedded parallel fractures. The model is based on Schoenberg’s linear-slip theory. Attenuation
is introduced by means of a complex-valued stiffness matrix, which includes complex-valued normal and tangential weaknesses.
To study the peculiarities of seismic attenuation versus wave-propagation direction in TI media, numerical modeling was performed.
The model-input data were the complex-valued weaknesses found from the laboratory ultrasonic experiment made with a Plexiglas
plate-stack model, oil-saturated (wet) and air-filled (dry). The laboratory experiment and the numerical modeling have shown
that in the vicinity of the symmetry axis, in the wet model, P-wave attenuation is close to S-wave attenuation, while in the
dry model, P-wave attenuation is much greater than S-wave attenuation. Moreover, the fluid fill affects the P-wave attenuation
pattern. In the dry (air-saturated) model, the attenuation pattern in the vicinity of the symmetry axis exhibits steeper slope
and curvature than in the wet (oil-saturated) model. To define the slope or the curvature, a QVO gradient was introduced,
which was found to be proportional to the symmetry-axis Q
S/Q
P-ratio, which explains the differences between dry and wet models. Thus, depending on the Q
S/Q
P-ratio, the QVO gradient can serve as an indicator of the type of fluid in fractures, because the QVO gradient is greater
in gas-saturated than in liquid-saturated rocks. The analysis of P-wave attenuation anisotropy in seismic reflection and vertical
seismic profiling data can be useful in seismic exploration for distinguishing gas from water in fractures. 相似文献
4.
Schoenflies motion is often termed X-motion for conciseness. A set of X-motions with a given direction of its axes of rotations has the algebraic properties of a Lie group for the composition product of rigid-body motions or displacements. The product of two X-subgroups, which is the mathematical model of a serial concatenation of two kinematic chains generating two distinct X-motions, characterizes a noteworthy type of 5-dimensional (5D) displacement set called double Schoenflies motion or X–X motion for brevity. This X–X motion set is a 5D submanifold of the displacement 6D Lie group. Such a motion type includes any spatial translation (3T) and any two sequential rotations (2R) provided that the axes of rotation are parallel to two fixed independent vectors. This motion set also contains the rotations that are products of the foregoing two rotations. In the paper, some preliminary fundamentals on the 4D X-motion are recalled; the 5D set of X–X motions is emphasized. Then implementing serial arrays of one-dof Reuleaux pairs and hinged parallelograms, we enumerate all serial mechanical generators of X–X motion, which have no redundant internal mobility. Based on the group-theoretic concepts, one can differentiate two families of irreducible representations of an X–X motion. One family is realized by twenty-one open chains including the doubly planar motion generators as special cases. The other is generally classified into eight major categories in which one hundred and six distinct open chains generating X–X motion are revealed and nineteen more ones having at least one parallelogram are derived from them. Meanwhile, these kinematic chains are graphically displayed for a possible use in the structural synthesis of parallel manipulators. 相似文献
5.
Yu. A. Abzaev 《Journal of Applied Mechanics and Technical Physics》2007,48(4):599-604
The temperature dependence of the yield stress τ*
Ni
3
Ge single crystals is studied. The temperature dependence τ*(T) in the high-temperature region (above 420 K) is found to be conditioned by thermally activated accumulation of the density of non-screw components of superdislocations.
Interaction of point defects with edge dislocations and its effect on the temperature anomaly of the yield stress in Ni
3
Ge single crystals are analyzed. The calculated results are found to agree with experimental data.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 4, pp. 154–161, July–August, 2007. 相似文献
6.
A. Ben-Artzi I. Gohberg M. A. Kaashoek 《Journal of Dynamics and Differential Equations》1993,5(1):1-36
A linear ordinary differential operator with bounded coefficients satisfying certain homogeneous initial conditions is shown to be invertible onL
n
2
(0, ) if and only if the underlying system of differential equations has a dichotomy. Moreover, in that case the operator is proved to be a direct sum of two infinitesimal generators ofC
0-semigroups, one of which has support on the negative half-line and the other on the positive half-line. The effect of perturbations of the initial values on the dichotomy is also described. 相似文献
7.
This paper describes a practical method for finding the invariant orbits in J
2 relative dynamics. Working with the Hamiltonian model of the relative motion including the J
2 perturbation, the effective differential correction algorithm for finding periodic orbits in three-body problem is extended
to formation flying of Earth’s orbiters. Rather than using orbital elements, the analysis is done directly in physical space,
which makes a direct connection with physical requirements. The asymptotic behavior of the invariant orbit is indicated by
its stable and unstable manifolds. The period of the relative orbits is proved numerically to be slightly different from the
ascending node period of the leader satellite, and a preliminary explanation for this phenomenon is presented. Then the compatibility
between J
2 invariant orbit and desired relative geometry is considered, and the design procedure for the initial values of the compatible
configuration is proposed. The influences of measure errors on the invariant orbit are also investigated by the Monte–Carlo
simulation.
The project supported by the Innovation Foundation of Beihang University for Ph.D. Graduates, and the National Natural Science
Foundation of China (60535010). 相似文献
8.
This paper investigates robust filter design for linear discrete-time impulsive systems with uncertainty under H∞ performance. First, an impulsive linear filter and a robust H∞ filtering problem are introduced for a discrete-time impulsive systems. Then, a sufficient condition of asymptotical stability and H∞ performance for the filtering error systems are provided by the discrete-time Lyapunov function method. The filter gains can be obtained by solving a set of linear matrix inequalities (LMIs). Finally, a numerical example is presented to show effectiveness of the obtained result. 相似文献
9.
By using the Z
p
geometrical index theory, some sufficient conditions on the multiplicity results of periodic solutions to the second-order difference equations
are obtained. By two examples, we show that our results are the best possible in the sense that the lower bound of the number of periodic solutions cannot be improved. 相似文献
10.
TheT
ε
*
integral was calculated on the surface of single edge notched, three-point bend (SE(B)) specimens using experimentally obtained
displacements. Comparison was made withT
ε
*
calculated with the measured surface displacements andT
ε
*
calculated at several points through the thickness of a finite element (FE) model of the SE(B) specimen. Good comparison
was found between the surfaceT
ε
*
calculated from displacements extracted from the FE model and the surfaceT
ε
*
calculated from experimentally obtained displacements. The computedT
ε
*
integral was also observed to decrease as the crack front was traversed from the surface to the mid-plane of the specimen.
Mid-planeT
ε
*
values tend to be approximately 10% of the surface values. 相似文献
11.
F.W. Wu R.N. Ibrahim R. Das R.K. Singh Raman 《Theoretical and Applied Fracture Mechanics》2009,52(1):50-54
Many approaches for estimating mode I fracture toughness (KIC) using circumferentially notched tensile (CNT) specimen have been demonstrated in the literature. In this paper, an effective approach for estimating fracture toughness from the numerical solution of critical crack tip opening displacement (CTOD) is proposed. An elasto-plastic finite element analysis is used to estimate critical CTOD values for CNT specimens. A number of materials are analysed, and the relationship between KIC and critical CTOD for CNT specimens is obtained. The proposed relationship is validated by comparing the fracture toughness values obtained from the relationship with those obtained experimentally using CNT specimens. The fracture toughness (KIC) calculated according to this relationship from numerically obtained critical CTOD is found to be in close agreement with the experimentally obtained fracture toughness for the respective materials. 相似文献
12.
The purpose of this study is to investigate the accuracy of the least squares method for finding the in-plane stress intensity factorsK
I
andK
II
using thermoelastic data from isotropic materials. To fully understand the idealized condition ofK
I
andK
II
calculated from thermoelastic experiments, the total stress field calculated from finite element analysis is used to take the place of data obtained from real thermoelastic experiments. In the finite element analysis, theJ-integral is also calculated to compare with (K
I
2
+K
II
2
)/E evaluated by the least squares method. The stress fields near the crack tip are dominated by the two stress intensity factors; however, the edge effect will cause inaccuracy of the thermoelastic data near the crack tip. Furthermore, the scan area of thermoelastic experiments cannot be too small. Therefore, we suggest that three or four terms of stress function be included in the least squares method for evaluating stress intensity factors via the thermoelastic technique. In the idealized condition, the error can be smaller than 3 percent from our numerical simulations. If only ther
–1/2 term (K
I
andK
II
) is included in the least squares method, even in the idealized case the error can be up to 20 percent. 相似文献
13.
Paolo Vannucci 《Journal of Elasticity》2002,67(2):81-96
This paper shows the existence of a particular type of planar orthotropic material, here denoted for the sake of brevity as
R
0-orthotropic. The number of independent elastic constants for these materials is three, and not four as for a general orthotropic
layer, but these constants have only two orthogonal axes of symmetry. The way to obtain a R
0-orthotropic layer is discussed in the paper, along with the advantages in its use.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
14.
To investigate the viscoelastic behavior of fluid dispersions under steady shear flow conditions, an apparatus for parallel superimposed oscillations has been constructed which consists of a rotating cup containing the liquid under investigation in which a torsional pendulum is immersed. By measuring the resonance frequency and bandwidth of the resonator in both liquid and in air, the frequency and steady-shear-rate-dependent complex shear modulus can be obtained. By exchange of the resonator lumps it is possible to use the instrument at four different frequencies: 85, 284, 740, and 2440 Hz while the steady shear rate can be varied from 1 to 55 s–1. After treatment of the theoretical background, design, and measuring procedure, the calibration with a number of Newtonian liquids is described and the accuracy of the instrument is discussed.Notation
a
radius of the lump
-
A
geometrical constant
-
b
inner radius of the sample holder
-
c
constant
-
C
1, C
2
apparatus constants
-
D
damping of the pendulum
-
e
x
, e
y
, e
z
Cartesian basis
-
e
r
, e
, e
z
orthonormal cylindrical basis
-
E
geometrical constant
-
E
t
, 0
E
t
,
t
relative strain tensor
-
f
function of shear rate
-
F
t
relative deformation tensor
-
G
(t)
memory function
-
G
*
complex shear modulus
-
G
Re(G
*
)
-
G
Im(G
*
)
-
h
distance between plates
-
H
*
transfer function
-
,
functional
-
i
imaginary unit: i
2= – 1
-
I
moment of inertia
-
J
exc
excitation current
-
J
0
amplitude of J
exc
-
k
* = k – ik
complex wave number
-
K
torsional constant
-
K
fourth order tensor
-
l
length of the lump
-
L
mutual inductance
-
M
dr
driving torque
-
M
liq
torque exerted by the liquid
-
0
M
liq,
liq
steady state and dynamic part of Mliq
-
n
power of the shear rate
-
p
isotropic pressure
-
Q
quality factor
-
r
radial position
-
R,R
0, R
c
Re(Z
*, Z
0
*
, Z
c
*
)
-
s
time
-
t, t
time
-
T
temperature
-
T, 0
T,
stress tensor
-
u
velocity
-
U
lock-in output
- 0
velocity
-
V
det
detector output voltage
-
V
sig, V
cr
signal and cross-talk part of V
det
-
x
Cartesian coordinate
-
X , X
0, X
c
Im(Z
*, Z
0
*
, Z
c
*
)
-
y
Cartesian coordinate
-
z
Cartesian coordinate, axial position 相似文献
15.
First of all, the concept of γ-p-Sa-Sm-N (confidence level-relabilitystress amplitude-stress mean-fatigue life) surface is presented. Then the formulas of p-Sa-Sm-N surface and γ-p-Sa-Sm-N surface are derived. In addition, fatigue strength distribution function and two-dimensional reliability Miner rule are
obtained. At last, an example is given.
Foundation item: the National Natural Science Foundation of China (19672051) 相似文献
16.
Zhao Kai Associate Professor 《应用数学和力学(英文版)》2000,21(5):573-578
Let B be a Banach space in UMD with an unconditional basis. The boundedness of the θ(t)-type singular integral operators in
L
B
p
(R
n), (1≤p<+∞) and H
B
1
(R
n) spaces are discussed.
Foundation item: the Education Commission of Shandong Province (J98P51)
Biography: Zhao Kai (1960-) 相似文献
17.
When using H∞ techniques to design decentralized controllers for large systems,the whole system is divided into subsystems, which are analysed using H∞ control theorybefore being recombined. An analogy was established with substructural analysis instructural mechanics, in which H∞ decentralized control theory corresponds to substructuralmodal synthesis theory so that the optimal H∞ norm of the whole system corresponds to thefundamental vibration frequency of the whole structure. Hence, modal synthesismethodology and the extended Wittrick-Williams algorithm were transplanted from structuralmechanics to compute the optimal H∞ norm of the control system. The orthogonality and theexpansion theorem of eigenfunctions of the subsystems H∞ control are presented in part(I) of the paper. The modal synthesis method for computation of the optimal H∞ norm ofdecentralized control systems and numerical examples are presented in part (Ⅱ). 相似文献
18.
丁协平 《应用数学和力学(英文版)》2007,28(12):1569-1579
This paper is a continuum of the preceding paper of author. Some new systems of generalized vector quasi-equilibrium problems
involving condensing mappings are introduced and studied in locally FC-uniform spaces. By applying the existence theorem of maximal elements of condensing set-valued mappings in locally FC-uniform spaces obtained by author in the preceding paper, some new existence theorems of solutions for the systems of generalized
vector quasi-equilibrium problems are proved in locally FC-uniform spaces. These results improve and generalize some known results in literature to locally FC-uniform spaces.
Project supported by the Natural Science Foundation of Sichuan Education Department of China (No. 2003A081 and SZD0406) 相似文献
19.
Effects of the stress state on plasticity and ductile failure of an aluminum 5083 alloy 总被引:2,自引:0,他引:2
Xiaosheng Gao Tingting Zhang Matthew Hayden Charles Roe 《International Journal of Plasticity》2009,25(12):2366-2382
The experimental and numerical work presented in this paper reveals that stress state has strong effects on both the plastic response and the ductile fracture behavior of an aluminum 5083 alloy. As a result, the hydrostatic stress and the third invariant of the stress deviator (which is related to the Lode angle) need to be incorporated in the material modeling. These findings challenge the classical J2 plasticity theory and provide a blueprint for the establishment of the stress state dependent plasticity and ductile fracture models for aluminum structural reliability assessments. Further investigations are planned to advance, calibrate and validate the new plasticity and ductile fracture models. 相似文献
20.
For a crack subjected to combined mode I and III loading the influence of a T-stress is analyzed, with focus on crack growth. The solid is a ductile metal modelled as elastic–plastic, and the fracture process is represented in terms of a cohesive zone model. The analyzes are carried out for conditions of small scale yielding, with the elastic solution applied as boundary conditions on the outer edge of the region analyzed. For several combinations of the stress intensity factors KI and KIII and the T-stress crack growth resistance curves are calculated numerically in order to determine the fracture toughness. In all situations it is found that a negative T-stress adds to the fracture toughness, whereas a positive T-stress has rather little effect. For given values of KI and T the minimum fracture toughness corresponds to KIII = 0. 相似文献