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1.
A micromechanical model is developed to simulate the mechanical behaviors of discontinuous reinforced composites. The analysis
for a representative unit cell is based on the assumption of a periodic array of aligned reinforcements. The minimum energy
principle is used to determine the unknown coefficients of the displacement field of the unit cell. The constitutive behavior
of composites is studied to obtain the relationship between the main variables of matrix and reinforcements. It is concluded
that the flow strength of composites is strongly influenced by volume fraction, aspect ratio of reinforcement, and the strain
hardening exponent of matrix. An analytical constitutive relation of composites is obtained. The predicted results are in
agreement with the existing experimental and numerical results.
The project supported by the National Natural Science Foundation of China (19704100) and National Science Foundation of Chinese
Academy of Sciences (KJ951-1-20) 相似文献
2.
The distribution of stress and strain fields in a micro-structural area of a particle reinforced composite is studied by a
combination of experimental and numerical method (hybrid method). With the experimental values of displacements in a micro-region
as the boundary loading condition, strain and stress fields inside the micro-region are calculated by the finite element method
under two different kinds of modeling, namely, as plane stress and plane strain condition. The differences between the two
kinds of modeling conditions as applied to micro-structural areas are discussed.
Project Supported by the National Natural Science Foundation of China (19972046) and National Overseas Study Foundation. 相似文献
3.
Based on the general solution given to a kind of linear tensor equations, the spin of a symmetric tensor is derived in an
invariant form. The result is applied to find the spins of the left and the right stretch tensors and the relation among different
rotation rate tensors has been discussed. According to work conjugacy, the relations between Cauchy stress and the stresses
conjugate to Hill's generalized strains are obtained. Particularly, the logarithmic strain, its time rate and the conjugate
stress have been discussed in detail. These results are important in modeling the constitutive relations for finite deformations
in continuum mechanics.
The project is supported by the National Natural Science Foundation of China and the Chinese Academy of Sciences (No. 87-52). 相似文献
4.
The mode I plane strain crack tip field with strain gradient effects is presented in this paper based on a simplified strain
gradient theory within the framework proposed by Acharya and Bassani. The theory retains the essential structure of the incremental
version of the conventionalJ
2 deformation theory. No higher-order stress is introduced and no extra boundary value conditions beyond the conventional ones
are required. The strain gradient effects are considered in the constitutive relation only through the instantaneous tangent
modulus. The strain gradient measures are included into the tangent modulus as internal parameters. Therefore the boundary
value problem is the same as that in the conventional theory. Two typical crack problems are studied: (a) the crack tip field
under the small scale yielding condition induced by a linear elastic mode-IK-field and (b) the complete field for a compact tension specimen. The calculated results clearly show that the stress level
near the crack tip with strain gradient effects is considerable higher than that in the classical theory. The singularity
of the strain field near the crack tip is nearly equal to the square-root singularity and the singularity of the stress field
is slightly greater than it. Consequently, theJ-integral is no longer path independent and increases monotonically as the radius of the calculated circular contour decreases.
The project supported by the National Natural Science Foundation of China (19704100 and 10202023) and the Natural Science
Foundation of Chinese Academy of Sciences (KJ951-1-20) 相似文献
5.
Wei Yueguang 《Acta Mechanica Sinica》2001,17(1):45-58
The influences of particle size on the mechanical properties of the particulate metal matrix composite are obviously displayed
in the experimental observations. However, the phenomenon can not be predicted directly using the conventional elastic-plastic
theory. It is because that no length scale parameters are involved in the conventional theory. In the present research, using
the strain gradient plasticity theory, a systematic research of the particle size effect in the particulate metal matrix composite
is carried out. The roles of many composite factors, such as: the particle size, the Young's modulus of the particle, the
particle aspect ratio and volume fraction, as well as the plastic strain hardening exponent of the matrix material, are studied
in detail. In order to obtain a general understanding for the composite behavior, two kinds of particle shapes, ellipsoid
and cylinder, are considered to check the strength dependence of the smooth or non-smooth particle surface. Finally, the prediction
results will be applied to the several experiments about the ceramic particle-reinforced metal-matrix composites. The material
length scale parameter is predicted.
The project supported by the National Natural Science Foundation of China (19891180, 19925211) and by the Chinese Academy
of Sciences (KJ951-1-201) and “Bai Ren” plan 相似文献
6.
A constitutive relation to describe pseudo-elastic deformation in shape memory alloys is presented in this paper. It is capable
of describing deformation behaviour of polycrystalline materials under triaxial stress state as well as of monocrystalline
materials under one-dimensional condition. Total strain rate is supposed to be composed of elastic strain rate and transformation
strain rate. Deformation behaviour of Cu−Zn−Sn alloy and Ti−ni alloy is simulated by use of the proposed constitutive relation.
it is shown that simulated results are in a good agreement with experimental data.
The project supported by National Natural Science Foundation of China. 相似文献
7.
The OPCM strain gauges for strain and stress measurement of orthotropic material structures 总被引:4,自引:0,他引:4
The orthotropic mechanical sensor of piezoelectric composite material made from piezoelectric ceramic and resin materials
and their sensing mechanism are presented. The sensing equations of the adhered-and embedded-type sensing units are deduced,
which are used to detect the stresses in orthotropic material structures. The surface strain of the orthogonal plate is measured
under the action of the planar stress field, and the error is analyzed.
Supported by the National Natural Science Foundation (No. 59635640), the Science Foundation of Jiangsu Education Committe
(99KJD130001) and the Science Foundation of Jiangsu Province (BK99116). 相似文献
8.
Theoretical analysis on the local critical stress and size effect for interfacial debonding in particle reinforced rheological materials 总被引:1,自引:0,他引:1
The mechanisms of interfacial debonding of particle reinforced rheological materials are studied. Based on an energy criterion,
a simple formula of local critical stress for interfacial debonding is derived and expressed in terms of the interfacial energy.
The particle size effect on interface debonding can then be analyzed easily owing to the fact that critical stress is inversely
proportional to the square root of particle radius. By taking PP/CaCO3 system as an example, the present energy criterion is compared with the mechanical debonding criterion, and it is found that
under the condition that bond strength is equal to matrix strength and particle radius not over 0.2μm, the mechanical debonding
criterion can be automatically satisfied if the energy criterion is satisfied. A relation between critical time and interface
energy is calculated by using the energy criterion. The influences of the particle volume fraction and the parlicle size,
the loading rate and the relaxation time of the matrix on the critical time of interfacial debonding are also discussed.
Supported by the National Natural Science Foundation of China (19632030 and 19872007) and Natural Science Foundation of Jiangsu
Province. 相似文献
9.
Using strain energy-based prediction of effective elastic properties in topology optimization of material microstructures 总被引:1,自引:0,他引:1
Weihong Zhang Gaoming Dai Fengwen Wang Shiping Sun Hicham Bassir 《Acta Mechanica Sinica》2007,23(1):77-89
An alternative strain energy method is proposed for the prediction of effective elastic properties of orthotropic materials
in this paper. The method is implemented in the topology optimization procedure to design cellular solids. A comparative study
is made between the strain energy method and the well-known homogenization method. Numerical results show that both methods
agree well in the numerical prediction and sensitivity analysis of effective elastic tensor when homogeneous boundary conditions
are properly specified. Two dimensional and three dimensional microstructures are optimized for maximum stiffness designs
by combining the proposed method with the dual optimization algorithm of convex programming. Satisfactory results are obtained
for a variety of design cases.
The project supported by the National Natural Science Foundation of China (10372083, 90405016), 973 Program (2006CB601205)
and the Aeronautical Science Foundation (04B53080). The English text was polished by Keren Wang. 相似文献
10.
The crack tip zone shielding effect for the ductile particle reinforced brittle materials is analyzed by using a micromechanics
constitutive theory. The theory is developed here to determine the elastoplastic constitutive behavior of the composite. The
elastoplastic particles, with isotropic or kinematical hardening, are uniformly dispersed in the brittle elastic matrix. The
method proposed is based on the Mori-Tanaka's concept of average stress in the composite. The macroscopic yielding condition
and the incremental stress strain relation of the composite during plastic deformation are explicity given in terms of the
macroscopioc applied stress and the microstructural parameters of the composite such as the volume fraction and yield stress
of ductile particles, elastic constants of the two phases, etc. Finally, the contribution of the plastic deformation in the
particles near a crack tip to the toughening of the composite is evaluated.
The project supported by National Natural Science Foundation of China 相似文献
11.
The strain gradient effect becomes significant when the size of fracture process zone around a crack tip is comparable to
the intrinsic material lengthl, typically of the order of microns. Using the new strain gradient deformation theory given by Chen and Wang, the asymptotic
fields near a crack tip in an elastic-plastic material with strain gradient effects are investigated. It is established that
the dominant strain field is irrotational. For mode I plane stress crack tip asymptotic field, the stress asymptotic field
and the couple stress asymptotic field can not exist simultaneously. In the stress dominated asymptotic field, the angular
distributions of stresses are consistent with the classical plane stress HRR field; In the couple stress dominated asymptotic
field, the angular distributions of couple stresses are consistent with that obtained by Huang et al. For mode II plane stress
and plane strain crack tip asymptotic fields, only the stress-dominated asymptotic fields exist. The couple stress asymptotic
field is less singular than the stress asymptotic fields. The stress asymptotic fields are the same as mode II plane stress
and plane strain HRR fields, respectively. The increase in stresses is not observed in strain gradient plasticity for mode
I and mode II, because the present theory is based only on the rotational gradient of deformation and the crack tip asymptotic
fields are irrotational and dominated by the stretching gradient.
The project supported by the National Natural Science Foundation of China (19704100), National Natural Science Foundation
of Chinese Academy of Sciences (KJ951-1-20), CAS K.C. Wong Post-doctoral Research Award Fund and Post-doctoral Science Fund
of China 相似文献
12.
The topological bifurcation diagrams and the coefficients of bifurcation equation were obtained by C-L method. According to obtained bifurcation diagrams and combining control theory, the method of robust control of periodic bifurcation was presented, which differs from generic methods of bifurcation control. It can make the existing motion pattern into the goal motion pattern. Because the method does not make strict requirement about parametric values of the controller, it is convenient to design and make it. Numerical simulations verify validity of the method. 相似文献
13.
Investigated in this paper are the effects of strain gradients on the stress distribution near an interface. The quasi axis-symmetry
interface problem is solved by using the couple stress theory and the perturbation method. The results show that a boundary
layer exists near an interface or a fixed boundary, where the shear stress perpendicular to the interface is significantly
different from that obtained from the classical elasticity theory.
Supported by the National Natural Science Foundation of China (No. 19891180). 相似文献
14.
In the framework of the two-fluid model, a hypersonic flow of a nonuniform dusty gas with low inertial (non-depositing) particles
around a blunt body is considered. The particle mass concentration is assumed to be small, so that the effect of particles
on the carrier phase is significant only inside the boundary layer where the particles accumulate. Stepshaped and harmonic
nonuniformities of the particle concentration ahead of the bow shock wave are considered and the corresponding nonstationary
distributions of the particle concentration in the shock layer are studied. On the basis of numerical study of nonstationary
two-phase boundary layer equations derived by the matched asymptotic expansion method, the effects of free-stream particle
concentration nonuniformities on the thermal flux, and the friction coefficient in the neighborhood of stagnation point are
investigated, in particular, the most “dangerous” nonuniformity periods are found.
The project supported by the Russian Foundation for Basic Research (project No. 96-01-00313) and the National Natural Science
Foundation of China (joint RFBR-NSFC grant No. 96-01-00017c) 相似文献
15.
The criterion for the points in the parameter space being on the stability boundary of linear Hamiltonian system depending
on arbitrary numbers of parameters was given, through the sensitivity analysis of eigenvalues and eigenvectors. The results
show that multiple eigenvalues with Jordan chain take a very important role in the stability of Hamiltonian systems.
Foundation item: the National Natural Science Foundation of China (10072012); the National Natural Science Foundation of Russia
Biography: QI Zhao-hui (1964-) 相似文献
16.
In this paper, a driving stress finite element method of elastic-plastic large deformation based on implicit time integrating
algorithm and an eight-chain molecular network model is used for the numerical simulation of the simple shear test of polycarbonate
(PC) materials. The simulated results are compared with experimental ones. The strain localization propagation for the shear
band deformation for simple shear deformation is investigated numerically. The effects of microstructure parameters in the
model on strain softening and orientation hardening of the PC are discussed in detail.
Supported by the National Natural Science Foundation of China. 相似文献
17.
An embedded cell model is presented to obtain the effective elastic moduli for three-dimensional two-phase composites which
is an exact analytic formula without any simplified approximation and can be expressed in an explicit form. For the different
cells such as spherical inclusions and cracks surrounded by sphere and oblate ellipsoidal matrix, the effective elastic moduli
are evaluated and the results are compared with those from various micromechanics models. These results show that the present
model is direct, simple and efficient to deal with three-dimensional two-phase composites.
The project supported by the National Natural Science Foundation of China (No. 19704100) and the National Natural Science
Foundation of Chinese Academy of Sciences (No. KJ951-1-201) 相似文献
18.
In this paper, a two dimensional Voronoi cell element, formulated with creep, thermal and plastic strain, is applied for the numerical simulation of thermo-mechanical fatigue behavior for particulate reinforced composites. The relation between mechanical fatigue phases and thermal fatigue phases influences the thermo-mechanical fatigue behavior and cyclic creep damage. The topological features of micro-structure in particulate reinforced composites, such as the orientation, depth-width ratio, distribution and volume fraction of inclusions, have a great influence on thermo-mechanical behavior. Some related conclusions are obtained by examples of numerical simulation.The project supported by the Special Funds for the National Major Fundamental Research Projects (2004CB619304), the National Natural Science Foundation of China (10276020 and 50371042), the Key Grant Project of Chinese Ministry of Education (0306) 相似文献
19.
According to the classical elastic theory, there is always a discontinuity of rotation angle on the interface between different
materials. This illogic result can be overcome by the strain gradient plasticity theory. In the light of this theory, there
is a group of boundary layer solutions near the interface, which have made important adjustment of the classical results.
This project is supported by National Natural Science Foundation of China (19891180). 相似文献
20.
A higher order asymptotic solution of near-tip field is studied for plane-atrain Mode-I quasi-static steady crack growth in
the incompressible (v=1/2) elastic perfectly-plastic media. The results show that the near-tip stress and strain are fully continuous, and the
strain possesses In (A/r) singularity at the crack tip. The expressions of the stress, strain and velocity in each region are also given.
The project supported by National Natural Science Foundation of China 相似文献