共查询到20条相似文献,搜索用时 28 毫秒
1.
William N. Sharpe Jr. 《Experimental Mechanics》1992,32(1):62-67
In principle, one should be able to measure elastoplastic stresses in the same manner as one does elastic stresses; i.e.,
measure the strains and compute the stresses from the constitutive law. In practice, this is rarely done because of the more
complicated material response and the anisotropy of the plastic behavior. Further, elastoplastic stresses should be computed
incrementally in the general case.
This paper presents procedures for computing stresses from elastoplastic strains measured incrementally in a test under microcomputer
control. The approach is evaluated for four different materials—two obeying the assumptions of classical plasticity and two
showing anisotropic behavior—by computing the stresses in a smooth specimen from measured principal strains. A useful application
is presented by computing the stresses at a notch root from biaxial strains measured with laser-based interferometry.
The general conclusion is that even in situations where the material is clearly anisotropic, this approach can give a reasonableestimate of the largest local principal stress.
Paper was presented at the 1991 SEM Spring Conference on Experimental Mechanics held in Milwaukee, WI on June 9–13. 相似文献
2.
TWO-DIMENSIONALDEFORMATIONOFANANISOTROPICELASTICBODYWITHAPARABOLICBOUNDARYHuYuan-tai(胡元太)ZhaoXing-hua(赵兴华)(ShanghaiUniversity... 相似文献
3.
Large Eddy Simulation has been applied to a piloted methane/air diffusion flame—the Sandia D flame—for which detailed experimental
data are available. To evaluate the reacting density, temperature and species mass fractions a conserved scalar laminar flamelet
formulation is employed, utilising a single virtually unstrained flamelet. The results of two simulations are discussed, comparing
the use of the standard Smagorinsky model and a dynamic variant for closure of the unknown sub-grid stress. The chosen sub-grid
scale model is shown to be extremely influential on the final solution. Whilst the use of the standard model results in a
relatively poor simulation the dynamic closure offers an excellent velocity field prediction throughout the flame. Although
the flame does show some strain rate influence on burning, particularly close to the inlet nozzle, the relatively simple ‘unstrained’
flamelet model applied is shown to provide an accurate representation of temperature and major species distribution. 相似文献
4.
Yu. G. Tynnikov N. A. Tolstokulakov V. A. Ivanov V. A. Andrianov 《Journal of Applied Mechanics and Technical Physics》1998,39(3):342-348
The reusable source of a pulsed magnetic field—a ballistic magnetocumulative generator (BMG)—is considered. Electrical engineering analysis of the efficiency of operation of the generator on an active-inductive load
is performed. A method for calculating the two-dimensional distribution of the field in the busbars of the generator is developed.
Experimental results are obtained for the operation of aBMG model on some types of load.
Central Scientific-Research Institute “Burevestnik,” Nizhnii Novgorod 603603. Translated from Prikladnaya Mekhanika i Tekhnicheskaya
Fizika, Vol. 39, No. 3, pp. 22–29, May–June, 1998. 相似文献
5.
V. P. Mulyar 《International Applied Mechanics》2006,42(1):98-102
A numerical analysis is made of the joint effect of two factors of asymmetry—ellipticity and eccentricity—on the stress distribution
near a free hole in a spherical shell. The nature of deformation is determined by the predominant factor. Whether there are
“fixed” points on the graphs of stress distribution around a small hole at which they intersect depends on how rigidly the
outer edge is fixed. As the rigidity of fixation is increased, the points smear
__________
Translated from Prikladnaya Mekhanika, Vol. 42, No. 1, pp. 113–118, January 2006. 相似文献
6.
A new interpretation of the concept of relative phase permeability is given. Relative phase permeabilities are represented
in the form of fourth-rank tensors. It is shown that in the case of anisotropic porous media functions depending not only
on the saturation but also on the anisotropy parameters represented in the form of ratios of the principal values of the absolute
permeability coefficient tensor correspond to the classical representation of the relative phase permeabilities. For a two-phase
flow in anisotropic porous media with orthotropic and transversely-isotropic symmetry a generalized two-term Darcy’s law is
analyzed.
Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 2, pp. 87–94, March–April, 1998.
The work was carried out with support from the Russian Foundation for Fundamental Research (project No. 96-01-00623). 相似文献
7.
We consider a nematic elastomer which has been cross-linked in an isotropic state. As an application, we consider the time-independent, isochoric, homogeneous deformation of a right circular cylinder wherein each circular cross section of the specimen is deformed into an ellipse. We explore the possibility of the existence of disclinations when the molecular conformation is uniaxial. Numerical solution of the governing boundary-value problem indicates the presence of an isotropic core (the disclination core) of material surrounding the cylinder axis in which the polymeric chains are shaped as spherical coils. The isotropic core is bounded by a narrow transition layer across which the molecular conformation changes from spherical to uniaxial. The material thereby becomes anisotropic away from the disclination. The anisotropic regions show a markedly different distribution for the free energy. This distribution of energy determines the radius of the core to be on the order of 10−2 μm. This work is a first step toward gaining an understanding of the existence of defective states in homogenous deformed nematic elastomers. 相似文献
8.
Luca Placidi Ralf Greve Hakime Seddik Sérgio H. Faria 《Continuum Mechanics and Thermodynamics》2010,22(3):221-237
A complete theoretical presentation of the Continuum-mechanical, Anisotropic Flow model, based on an anisotropic Flow Enhancement
factor (CAFFE model) is given. The CAFFE model is an application of the theory of mixtures with continuous diversity for the
case of large polar ice masses in which induced anisotropy occurs. The anisotropic response of the polycrystalline ice is
described by a generalization of Glen’s flow law, based on a scalar anisotropic enhancement factor. The enhancement factor
depends on the orientation mass density, which is closely related to the orientation distribution function and describes the
distribution of grain orientations (fabric). Fabric evolution is governed by the orientation mass balance, which depends on
four distinct effects, interpreted as local rigid body rotation, grain rotation, rotation recrystallization (polygonization)
and grain boundary migration (migration recrystallization), respectively. It is proven that the flow law of the CAFFE model
is truly anisotropic despite the collinearity between the stress deviator and stretching tensors. 相似文献
9.
Morphological measurements in 3D for pore space characterization (connectivity pore-body/throat classification, shape factors,
virtual fluid intrusion) are based on computed intensive digital-thinning operations for skeletonization and medial axis extraction
from 3D digital images. We present an alternative method that is measurably faster and allows sub-voxel definition of the
pore space network. The method allows extracting—based on morphological considerations only—the centered and shortest stream-lines—i.e.,
the paths—to follow in order to go through the pore space from one given point to another and to exit. In addition the method
penalizes long and narrow pore-throats in favor of short stubby/ones—i.e., it has a built-in exemplification capacity. It
exploits well-established mathematical methods successfully applied in medical endoscopy. 相似文献
10.
V. N. Nikolaevskiy S. M. Kapustyanskiy M. Thiercelin A. G. Zhilenkov 《Transport in Porous Media》2006,65(3):485-504
Non-elastic pore deformations and crack propagations are the principal causes of dynamic damage in rocks and soils. In the
case of downhole blasting from wellbores, these two mechanisms compete with each other. Therefore, to carry out a mechanical
analysis of rock blasting, a sufficiently complete model that takes these various mechanisms into account has to be developed.
To address this issue, this paper proposes the use of an elastic–plastic model, which includes a yield condition with a non-associated
plastic flow rule, the effects of pore fluid saturation, and a brittle failure criterion under extension. The results presented
in this paper describe underground explosions with spherical motion (cavity growth under the internal pressure of detonated
gases without leakage into the formation), typical for oil or water reservoirs. The governing equations are written in a Cartesian
system of coordinates for the case of spatial dynamic medium deformation. For this case, Cartesian coordinates are more convenient
than spherical coordinates because they avoid numerical difficulties connected with the non-divergent terms of the non-linear
form of the Biot–Frenkel equations. The numerical method uses the Wilkins approach, which has been generalized for the model
described in this paper. The dilatancy of the material during plastic deformation is neglected for simplicity. The numerical
results show that, when using typical parameters for relatively “soft” porous skeleton, the plastic flow overcomes the brittle
failure. An extension zone only appears near the cavity. The results also show the presence of the two Biot P-waves. The second
Biot wave, however, is only seen in the case of an extremely high permeability rock. Furthermore, in the case of the first
Biot wave, the saturating liquid and the solid skeleton particles are moving with different velocities in a 100 darcy rock
and with the same velocity in a 0.01 darcy rock. Calculated radial particle velocities as a function of the scaled radius
are close to measured velocities in rigid dense media but are larger than measured ones in clays. It is suggested that the
difference is due to different levels of water saturation, assumed full saturation in the calculation, partial saturation
in the experiments. 相似文献
11.
A model composed of a three-dimensional orthogonal network of capillary tubes was used to simulate the flow behavior in an unsaturated anisotropic soil. The anisotropy in the network's permeability was introduced by randomly selecting the radii in the three mutually orthogonal directions of the network tubes from three different lognormal probability distributions, one for each direction. These three directions were assumed to be the principal directions of anisotropy. The sample was gradually drained, with only tubes smaller than a certain diameter remaining full at each degree of saturation. Computer experiments were conducted to determine the network's effective permeability as a function of saturation. The main conclusion was that the relationship between saturation and effective permeability depends on direction. Consequently the concept of relative permeability used in unsaturated flow should be limited to isotropic media and not extended to anisotropic ones. 相似文献
12.
Ladislav Ceniga 《Acta Mechanica Sinica》2010,26(5):695-709
This paper deals with an analytical model of thermal stresses which originate during a cooling process of an anisotropic solid continuum with uniaxial or triaxial anisotropy. The anisotropic solid continuum consists of anisotropic spherical particles periodically distributed in an anisotropic infinite matrix. The particles are or are not embedded in an anisotropic spherical envelope, and the infinite matrix is imaginarily divided into identical cubic cells with central particles. The thermal stresses are thus investigated within the cubic cell. This mulfi-particle-(envelope)-matrix system based on the cell model is applicable to two- and three-component materials of precipitate-matrix and precipitate-envelope-matrix types, respectively. Finally, an analysis of the determination of the thermal stresses in the multi-par- ticle-(envelope)-matrix system which consists of isotropic as well as uniaxial- and/or triaxial-anisotropic components is presented. Additionally, the thermal-stress induced elastic energy density for the anisotropic components is also derived. These analytical models which are valid for isotropic, anisotropic and isotropic-anisotropic multi-particle- (envelope)-matrix systems represent the determination of important material characteristics. This analytical determination includes: (1) the determination of a critical particle radius which defines a limit state regarding the crack initiation in an elastic, elastic-plastic and plastic components; (2) the determination of dimensions and a shape of a crack propagated in a ceramic components; (3) the determination of an energy barrier and micro-/macro-strengthening in a component; and (4) analytical-(experimental)-computational methods of the lifetime prediction. The determination of the thermal stresses in the anisotropic components presented in this paper can be used to determine these material characteristics of real two- and three-component materials with anisotropic components or with anisotropic and isotropic components. 相似文献
13.
In transport models for wood, sorption is an essential parameter. Sorption is the balancing process between the two phases
of water present in wood below the fiber saturation point, namely water vapor in the lumens and bound water in the cell walls.
To gain better insight into the physical background of transport processes, a special experimental test setup—the improved
cup method—is presented. It allows for separation of sorption from other processes. In this test, a diffusion cup contains
a thin specimen of wood, with one side facing outwards to a climate chamber and the opposite side facing inwards the cup.
In contrast to the common cup method, the herein presented method uses a data logger for relative humidity and temperature
placed inside the cup. The use of thin cross-cut specimens allows for explicit separation of the different processes occurring
during transient moisture transport. Mass changes were determined and relative humidity inside the cups was measured for eight
specimens of Norway spruce with different specimen thicknesses. Relative humidity was increased in three uniform steps in
the test chamber from 4.0 up to 76.5%. The results obtained with this special test setup indicate that the sorption process
is different than assumed in previous publications. This emphasizes the need of improved modeling approaches. 相似文献
14.
A fluorescence image analysis procedure to determine the distribution of species concentration and density in a gas flow is
proposed. The fluorescent emission is due to the excitation of atoms/molecules of a gas that is intercepted by an electron
sheet. The intensity of the fluorescent light is proportional to the local number density of the gas. When the gas flow is
a mixture of different species, this proportionality can be used to extract the contribution associated with the species from
the spectral superposition acquired by a digital camera. In particular, the fact is exploited such that the ratio between
a pair of color intensities takes different values for different gases and that different linear superpositions of different
color intensities yield a ratio that varies with the species concentration. This leads to a method that simultaneously reveals
species concentrations and mass density of the mixture. For the proper working of a continuous electron gun in a gas, the
procedure can be applied to gas flow where the pressure is below the thresholds of 200∼300 Pa and the number density is no
greater than 1023 m−3. To maintain the constancy of the emission coefficients, the temperature variation in the flow should be inside the range
75–900 K (above the temperature where the probability to meet disequilibrium phenomena due to rarefaction is low, below the
temperature where visible thermal emission is present). The overall accuracy of the measurement method is approximately 10%.
The uncertainty can vary locally in the range from 5 to 15% for the concentration and from 5 to 20% for the density depending
on the local signal-to-noise ratio. The procedure is applied to two under-expanded sonic jets discharged into a different
gas ambient—Helium into Argon and Argon into Helium—to measure the concentration and density distribution along the jet axis
and across it. A comparison with experimental and numerical results obtained by other authors when observing under-expanded
jets at different Mach numbers is made with the density distribution along the axis of the jet. This density distribution
appears to be self-similar. 相似文献
15.
The Iosipescu shear test, utilizing a notched specimen in bending and a modification—the asymmetrical four-point bend (AFPB)
test—were evaluated as shear tests for composites. This paper summarizes the results of an extensive numerical and experimental
investigation of the Iosipescu and AFPB test methods. Finite-element analyses were conducted to assess the influence of notch
parameters and load locations on the stress state in the specimen. The shear moduli and the shear strengths were experimentally
measured for a quasiisotropic graphite/epoxy laminate using both the Iosipescu and the AFPB test methods. The tests were conducted
for various combinations of notch parameters and load locations. The test results indicate that changes in the notch geometry
and load locations aimed at improving the stress distribution in the test section resulted in unexpected changes in the failure
mode.
Paper was presented at the 1985 SEM Spring Conference on Experimental Mechanics held in Las Vegas, NV on June 9–14. 相似文献
16.
Yu Shanbing 《Acta Mechanica Sinica》1992,8(4):363-373
This paper discribes a one-dimensional flow model to explain the basic mechanism of coal-gas outbursts. A break-start criterion
of coal, as the elementary outburst criterion, is given approximately. In this ideal model, the tectonic pressure before excavation,
as a load on coal body, affects the break-start and then the flow field. The flow field is decoupled with the stress field,
so that the gas seepage through unbroken coal body, break-start and consequent two-phase flow, and pure gas flow can be analysed
independently of the stress field.
The tunnelling, an external disturbance that makes the seepage intensify relatively, is an essential factor for initiating
outburst. Under steady tunnelling, seepage ought to tend to be steadily progressive. From its asymptotic solution initiation
criterion is obtained. This is described by three conditions, possibility condition —tectonic pressure condition, incubation
condition—tunnelling or gas condition and triggering condition —seepage velocity condition.
The project supported by the National Natural Science Foundation of China 相似文献
17.
The convective instability of mechanical equilibrium of an inclined plane layer of fluid developing under the action of a
static gravity field and high-frequency vibration is studied. Configurations corresponding to four directions of the equilibrium
temperature gradient — vertical, longitudinal, horizontal, and transverse — are considered for an arbitrary orientation of
the vibration axis. The stability limits and the characteristics of the critical perturbations are determined.
Perm’. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 1, pp. 8–15, January–February,
1998.
This investigation was carried out with partial support form RSA-NASA (contract No. 920/18 — 5208/96). 相似文献
18.
The thermoelastic problem for an infinite multiply connected anisotropic plate with holes and cracks in a linear heat flow
is solved. The stress distribution and the stress intensity factors on heat-insulated boundaries are analyzed numerically
__________
Translated from Prikladnaya Mekhanika, Vol. 41, No. 9, pp. 127–136, September 2005. 相似文献
19.
The paper presents a non-linear model of saturation with fluid of anisotropic capillary porous bodies and the results of experimental investigations of wood saturation with methacrylate. The obtained experimental curves illustrating the distribution of methacrylate in wood samples allow the estimation of material coefficients and verification of the theoretical model. The theoretical model is developed based on the balance equations of mass, momentum, and energy, and the thermodynamics of irreversible processes. The non-linear differential equation, describing the distribution of methacrylate content in wood and its evolution during the saturation is solved numerically. The theoretical curves obtained on the basis of both linear and non-linear models are compared with the experimental data and better agreement between them for the non-linear model is stated. 相似文献
20.
James T. Boyle 《Archive of Applied Mechanics (Ingenieur Archiv)》2012,82(4):495-514
High temperature design remains an issue for many components in a variety of industries. Although finite element analysis
for creep is now an accessible tool, most analyses outside the research domain use long standing and very simple constitutive
models—in particular based on a power law representation. However, for many years, it has been known that a range of materials
exhibit different behaviors at low and moderate stress levels. Recently, studies of the behavior of high temperature structures
with such a stress range-dependent constitutive model have begun to emerge. The aim of this paper is to examine further the
detailed behavior of simple structures with a modified power law constitutive model in order to instigate a deeper understanding
of such a constitutive model’s effect on stress and deformation and the implications for high temperature design. The structures
examined are elementary—a beam in bending and a pressurized thick cylinder—but have long been used to demonstrate the basic
characteristics of nonlinear creep. 相似文献