共查询到20条相似文献,搜索用时 922 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.
V. M. Greshnov I. V. Puchkova 《Journal of Applied Mechanics and Technical Physics》2010,51(2):280-287
This paper deals with mathematical modeling of one of the effective technologies of plastic metal forming — multistep cold
metal forging. Experimental results are given on the plastic behavior of metals under cyclic loading at large strains accumulated
for one cycle. Based on the experimental data obtained, a plasticity model is developed and shown to be effective in testing
and improving the technology of forging a nut blank by using a computer-aided engineering analysis system. 相似文献
3.
This work presents a wide number of results about the influence that variations in terms of operational and design parameters
play on the dynamic behavior of external gear pumps. These results are obtained by using a non-linear lumped-parameter kineto-elastodynamic
model developed and experimentally assessed with the aim of including all the important dynamic effects. On the one hand,
the effects of variations in the operational parameters—namely output pressure, rotational speed and oil viscosity—are analysed;
on the other hand, the effects of modifications of some design parameters are shown: clearances and relief groove dimension.
The results in terms of gear eccentricity, pressure evolution, pressure forces, gear accelerations and variable forces exciting
the pump casing enlighten the dynamic behavior of gear pumps and give useful indications for design improvements and vibration
and noise reduction. As regards specifically gear accelerations as well as forces exciting the casing, they strongly increase
with both output pressure and rotational speed, but variations in rotational speed in the operational range give lower effects.
Conversely, the modifications of the clearances give negligible effects, while the relief groove dimension is very important:
the larger the relief grooves are, the higher the gear accelerations and forces exciting the casing become. 相似文献
4.
J. L. C. Diniz R. D. Vieira J. T. Castro A. C. Benjamin J. L. F. Freire 《Experimental Mechanics》2006,46(6):765-775
This paper presents the analysis of stress and strain data acquired with the finite element method and with tests that used
post-yielding strain gages bonded onto the external surface of pipes that suffered thickness metal loss and that had been
loaded with internal pressure. These metal loss areas were produced by three different processes: actual internal corrosion,
careful machining of external patches by spark-erosion, and milling of internal or external patches to simulate limited or
extensive strip corrosion defects with depths up to 70% of the pipe’s thickness. Results show that: (1) the extensive longitudinal
internal or external defect areas behave as extensive strips with a high degree of freedom to deform elastically and plastically
in the circumferential and thickness directions, and (2) large restraints are offered to the longitudinal strains by the non-corroded
thick walls parallel to the strip. Using the above experimental observation, a simple mathematical model was developed to
predict the burst pressure of pipes with longitudinal extensive and reasonably constant depths of metal loss. This model employed
thin-pipe-strength-of-material equations associated to a bulging correction factor, the material’s uniaxial ultimate strength
and the von Mises criterion. The onset of plastic collapse predicted by the simple model was successfully compared with results
determined from actual hydrostatic tests that were carried out with full scale pipe specimens and from finite element results
generated by the use of a commercial program. The developed model was also helpful in showing that the yield and burst behaviors
of new or corroded pipeline specimens under laboratory test conditions can be directly compared and extended to the yield
and burst behaviors of buried pipeline in field operation. 相似文献
5.
The stability of a surface-charged cylindrical jet in a longitudinal uniform electric field with respect to capillary pertubations
is investigated in the linear approximation. The evolution of both axisymmetric and azimuthal-periodic perturbations is analyzed.
In the latter case the first two modes among the azimuthal wavenumbers — bending and Bohr — are considered. Axisymmetric and
bending instabilities lead to the transverse disintegration of the jet into individual drops and the Bohr mode to the longitudinal
separation of the input jet into two parts. It is found that the axisymmetric and bending instabilities, respectively, can
be completely suppressed and significantly attenuated by means of an external longitudinal field. In this case the role of
the Bohr mode becomes more important leading under certain conditions to longitudinal longwave jet splitting. Events which
can be interpreted as manifestations of longitudinal partition of the jet (dumbbell-like cross-section, branching nodes) are
observed in experiments with evaporating polymer-solution microjets.
Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 2, pp. 29–40, March–April, 1998.
The work was carried out with support from the Russian Foundation for Fundamental Research (project No. 97-01-00153). 相似文献
6.
7.
The predictions for plastic buckling of shells are significantly affected by the plasticity model employed, in particular in the case of nonproportional loading. A series of experiments on plastic buckling of cylindrical aluminum alloy shells under biaxial loading (external pressure and axial tension), with well-defined loading and boundary conditions, was therefore carried out to provide experimental data for evaluation of the suitability of different, plasticity models. In the experiments, initial imperfections and their growth under load were measured and special attention was paid to buckling detection and load path control. The Southwell plot was applied with success to smooth the results. The results show that axial tension decreases resistance to buckling under external pressure in the plastic region due to softening of the material behavior. Comparison with numerical calculations usingJ
2 deformation and incremental theories indicate that both theories do not predict correctly plastic buckling under nonproportional loading.Babcock (SEM Member), deceased, was Professor of Aeronautics and Applied Mechanics, California Institute of Technology, Pasadena, CA 91125. 相似文献
8.
《International Journal of Solids and Structures》2007,44(7-8):2304-2323
The homogenization technique is used to obtain an elastoplastic stress–strain relationship for dry, saturated and unsaturated granular materials. Deformation of a representative volume of material is generated by mobilizing particle contacts in all orientations. In this way, the stress–strain relationship can be derived as an average of the mobilization behavior of these local contact planes. The local behavior is assumed to follow a Hertz–Mindlin’s elastic law and a Mohr–Coulomb’s plastic law. For the non-saturated state, capillary forces at the grain contacts are added to the contact forces created by an external load. They are calculated as a function of the degree of saturation, depending on the grain size distribution and on the void ratio of the granular assembly. Numerical simulations show that the model is capable of reproducing the major trends of a partially saturated granular assembly under various stress and water content conditions. The model predictions are compared to experimental results on saturated and unsaturated samples of silty sands under undrained triaxial loading condition. This comparison shows that the model is able to account for the influence of capillary forces on the stress–strain response of the granular materials and therefore, to reproduce the overall mechanical behavior of unsaturated granular materials. 相似文献
9.
A method of stress—strain analysis of elastoplastic bodies with large displacements, rotations, and finite strains is developed.
The incremental loading technique is used within the framework of the arbitrary Lagrangian—Eulerian formulation. Constitutive
equations are derived which relate the Jaumann derivative of the Cauchy—Euler stress tensor and the strain rate. The spatial
discretization is based on the FEM and multilinear three-dimensional isoparametric approximation. An algorithm of stress—strain
analysis of elastic, hyperelastic, and perfectly plastic bodies is given. Numerical examples demonstrate the capabilities
of the method and its software implementation
__________
Translated from Prikladnaya Mekhanika, Vol. 41, No. 6, pp. 36–43, June 2005. 相似文献
10.
Some possible alternative solutions of near-tip fields are studied for plane-strain Mode—I quasi-static steady crack growth
in incompressible (ν=1/2) elastic perfectly-plastic media. A group of four-sector solutions and a three-sector solution in
which the elastic-unloading region vanishes are given. Stress functions, plastic flow factors and plastic strains in each
region are also given.
Project supported by the State Education Commission under a funding program for Excellent University Young Faculties and National
Natural Science Foundation of China. 相似文献
11.
Hamid R. Ghorbani Jan K. Spelt 《International Journal of Solids and Structures》2006,43(25-26):7424-7449
A two-dimensional model has been developed for thermal stresses, elastic strains, creep strains, and creep energy density at the interfaces of short and long trilayer assemblies under both plane stress and plane strain conditions. Both linear (viscous) and non-linear creep constitutive behavior under static and cyclic thermal loading can be modeled for all layers. Interfacial stresses and strains are approximated using a combination of exact elasticity solutions and elementary strength of materials theories. Partial differential equations are linearized through a simple finite difference discretization procedure. The approach is mathematically straightforward and can be extended to include plastic behavior and problems involving external loads and a variety of geometries. The model can provide input data for thermal fatigue life prediction in solder or adhesive joints. For a typical solder joint, it is demonstrated that the predicted cyclic stress–strain hysteresis shows shakedown and a rapid stabilization of the creep energy dissipation per cycle in agreement with the predictions of finite element analysis. 相似文献
12.
Thermal deformations and stresses were studied in a silicon-carbide/aluminum filamentary composite at temperatures up to 370°C (700°F). Longitudinal and transverse thermal strains were measured with strain gages and a dilatometer. An elastoplastic micromechanical analysis based on a one-dimensional rule-of-mixtures model and an axisymmetric two-material composite cylinder model was performed. It was established that beyond a critical temperature thermal strains become nonlinear with decreasing longitudinal and increasing transverse thermal-expansion coefficients. This behavior was attributed to the plastic stresses in the aluminum matrix above the critical temperature. An elastoplastic analysis of both micromechanical models was performed to determine the stress distributions and thermal deformation in the fiber and matrix of the composite. While only axial stresses can be determined by the rule-of-mixtures model, the complete triaxial state of stress is established by the composite cylinder model. Theoretical predictions for the two thermal-expansion coefficients were in satisfactory agreement with experimental results. 相似文献
13.
Directional near-wall flow induced by the vibration of slender micro-pillars attached to a surface similar to ciliary structures
or grafted filaments is studied experimentally. The micro-pillar arrays are arranged in the form of a “V” approximating an
asymmetric fore-aft bundle shape often found in nature, too. A base-layer actuation is used to excite the micro-pillars to
oscillate in a vibratory pattern with maximum amplitude at the tips. Due to the specific shape of the bundle structure and
asymmetric boundary conditions of the oscillatory motion, the pillars perform a tilted beating motion—similar to cilia—with
a forward power stroke and a backward oriented recovery stroke or vice versa, depending on the boundary conditions of the
actuation. As a consequence of the cooperative beating motion and the fore-aft asymmetry of the shape of the bundle, a directional
streaming motion is induced by the pillars which increase with increasing streaming Reynolds number Re
S
. In addition to the net streaming effect, the flow in the space between the pillar bases exhibit a micro-scale swirling motion
around each of the structures with an efficient mixing behavior. Applied to micro-channels or wall-bounded flows, such structures
may act as locally distributed passive or active flow manipulation devices. The use of such cilia bundles in large numbers
on surfaces as passive structures for near-wall control in of boundary layer flows is feasible, too. 相似文献
14.
A computational thermo-metallographic and thermoelastoplastic model for the analysis of the quenching process is developed
and validated. The diffusive transfor-mations are modeled according to the Johnson–Mehl–Avrami–Kolmogorov model and the Scheil’s
additivity rule. Two different models are investigated for the non-diffusive transformation—the Koistinen–Marburger model
and the Yu model. A large displacement formulation is assumed for the deformation analysis, modeling the plastic behavior
of the material according to the Prandtl–Reuss model. Two different bilinear hardening models—the isotropic and the kinematic
hardening model—are used and compared. The model allows to evaluate the transient stress and strain distributions during the
quenching process, the final phases and hardness distributions, and to predict the residual stress and the final deformation
of the processed part. A good agreement between computational results and reference data is found 相似文献
15.
The geometrically nonlinear periodic vibrations of beams with rectangular cross section under harmonic forces are investigated
using a p-version finite element method. The beams vibrate in space; hence they experience longitudinal, torsional, and nonplanar bending
deformations. The model is based on Timoshenko’s theory for bending and assumes that, under torsion, the cross section rotates
as a rigid body and is free to warp in the longitudinal direction, as in Saint-Venant’s theory. The theory employed is valid
for moderate rotations and displacements, and physical phenomena like internal resonances and change of the stability of the
solutions can be investigated. Green’s nonlinear strain tensor and Hooke’s law are considered and isotropic and elastic beams
are investigated. The equation of motion is derived by the principle of virtual work. The differential equations of motion
are converted into a nonlinear algebraic form employing the harmonic balance method, and then solved by the arc-length continuation
method. The variation of the amplitude of vibration in space with the excitation frequency of vibration is determined and
presented in the form of response curves. The stability of the solution is investigated by Floquet’s theory. 相似文献
16.
This article presents the implementation of the constitutive model of Wheeler (Geotechnique 53(1):41–54, 2003) for coupling
of hydraulic hysteresis and mechanical behavior of unsaturated soils in a fully coupled transient hydro-mechanical finite
element (FE) model (computer code UNSATEX) developed by the authors. The constitutive model considers the effects of irreversible
changes of degree of saturation on stress–strain behavior and the influence of plastic volumetric strains on the water retention
behavior. The mathematical framework and the numerical implementation of the constitutive model are presented and discussed.
The FE model is verified and validated against analytical predictions [obtained using the model of Wheeler (Geotechnique 53(1):41–54,
2003] as well as experimental results from the literature involving unsaturated soils undergoing various combinations of drying,
wetting, loading, unloading, and reloading paths. Comparison of the results shows that the developed FE model can be used
to predict various aspects of the behavior of unsaturated soils under drying and wetting as well as loading and unloading
paths. The merits and limitations of the FE model are highlighted. 相似文献
17.
Theoretical identification of forces resisting longitudinal movement of drillstrings in curved wells
V. I. Gulyaev P. Z. Lugovoi S. N. Khudolii L. V. Glovach 《International Applied Mechanics》2007,43(11):1248-1255
The equations of balance of external and internal forces acting on a drillstring in a curved well are set up based on the
formulations of direct and inverse problems in the mechanics of flexible curvilinear rods. The lowering, lifting, and rotation
of a drillstring are studied. A method is proposed to calculate the internal longitudinal force, the forces of interaction
between the drillstring and the well wall, and the forces of friction. An example is considered. It is shown that even small
geometrical imperfections of the well path have a significant effect on the balance of external and internal forces
__________
Translated from Prikladnaya Mekhanika, Vol. 43, No. 11, pp. 80–89, November 2007. 相似文献
18.
19.
James G. Berryman 《Transport in Porous Media》2012,93(2):293-307
An algorithm is presented for inverting either laboratory or field poroelastic data for all the drained constants of an anisotropic
(specifically orthotropic) fractured poroelastic system. While fractures normally weaken the system by increasing the mechanical
compliance, any liquids present in these fractures are expected to increase the stiffness somewhat, thus negating to some
extent the mechanical weakening influence of the fractures themselves. The analysis presented in this article quantifies these
effects and shows that the key physical variable needed to account for the pore-fluid effects is a factor of (1 − B), where B is Skempton’s second coefficient and satisfies 0 ≤ B < 1. This scalar factor uniformly reduces the increase in compliance due to the presence of communicating fractures, thereby
stiffening the fractured composite medium by a predictable amount. One further aim of the discussion is to determine the number
of the poroelastic constants that needs to be known by other means to determine the rest from remote measurements, such as
seismic wave propagation data in the field. Quantitative examples arising in the analysis show that, if the fracture aspect
ratio af @ 0.1{a_f \simeq 0.1} and the pore fluid is liquid water, then for several cases considered, Skempton’s B @ 0.9{B \simeq 0.9}, and so the stiffening effect of the pore-liquid reduces the change in compliance due to the fractures by a factor 1 - B @ 0.1{1 - B \simeq 0.1}, in these examples. The results do, however, depend on the actual moduli of the unfractured elastic material, as well as
on the pore-liquid bulk modulus, so these quantitative predictions are just examples, and should not be treated as universal
results. Attention is also given to two previously unremarked poroelastic identities, both being useful variants of Gassmann’s
equations for homogeneous—but anisotropic—poroelasticity. Relationships to Skempton’s analysis of saturated soils are also
noted. The article concludes with a discussion of alternative methods of analyzing and quantifying fluid-substitution behavior
in poroelastic systems, especially for those systems having heterogeneous constitution. 相似文献
20.
D. D. Tjahjanto S. Turteltaub A. S. J. Suiker 《Continuum Mechanics and Thermodynamics》2008,19(7):399-422
The microstructure of multiphase steels assisted by transformation-induced plasticity consists of grains of retained austenite
embedded in a ferrite-based matrix. Upon mechanical loading, retained austenite may transform into martensite, as a result
of which plastic deformations are induced in the surrounding phases, i.e., the ferrite-based matrix and the untransformed
austenite. In the present work, a crystallographically based model is developed to describe the elastoplastic transformation
process in the austenitic region. The model is formulated within a large-deformation framework where the transformation kinematics
is connected to the crystallographic theory of martensitic transformations. The effective elastic stiffness accounts for anisotropy
arising from crystallographic orientations as well as for dilation effects due to the transformation. The transformation model
is coupled to a single-crystal plasticity model for a face-centered cubic lattice to quantify the plastic deformations in
the untransformed austenite. The driving forces for transformation and plasticity are derived from thermodynamical principles
and include lower-length-scale contributions from surface and defect energies associated to, respectively, habit planes and
dislocations. In order to demonstrate the essential features of the model, simulations are carried out for austenitic single
crystals subjected to basic loading modes. To describe the elastoplastic response of the ferritic matrix in a multiphase steel,
a crystal plasticity model for a body-centered cubic lattice is adopted. This model includes the effect of nonglide stresses
in order to reproduce the asymmetry of slips in the twinning and antitwinning directions that characterizes the behavior of
this type of lattices. The models for austenite and ferrite are combined to simulate the microstructural behavior of a multiphase
steel. The results of the simulations show the relevance of including plastic deformations in the austenite in order to predict
a more realistic evolution of the transformation process.
This work is part of the research program of the Netherlands Institute for Metals Research (NIMR) and the Stichting voor Fundamenteel Onderzoek der Materie (FOM, financially supported by the Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO)). The research was carried out under project number 02EMM20 of the FOM/NIMR program “Evolution of the Microstructure
of Materials” (P-33). 相似文献