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1.
Description of the elastic deformation and degradation of elastic properties of dispersedly failing isotropic materials 总被引:1,自引:1,他引:0
A model is put forward for describing the elastic deformation of a quasi-homogeneous isotropic material capable of accumulating
scattered microdamages during loading, which eventually leads to its total failure. The degree of damage of the material at
a point is characterized by a centrosymmetric scalar function on the unit sphere, named the damage function, whose values
depend on a dimensionless equivalent stress. This function is approximated by a fourth-rank tensor, which is used to construct
a constitutive relation between stresses and strains in a differential form. By way of example, the elastic deformation of
concrete and the degradation of its linearly elastic properties are described, and the basic three-dimensional sections of
the corresponding strength surface are constructed.
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Translated from Mekhanika Kompozitnykh Materialov, Vol. 42, No. 2, pp. 193–208, March–April, 2006. 相似文献
2.
Yu. M. Tarnopol'skii V. L. Kulakov D. D. Mungalov 《Mechanics of Composite Materials》1999,35(5):365-372
The advisability of application of advanced composites in deep-water offshore technology is shown using risers and tendons
as examples. Numerical estimations of the parameters of multilayered metal-composite risers are obtained. Two new processes
of spatial braiding for creating the external jackets of compound tendons are considered. Advanced composites are the only
possible choice for exploitation of deposits at depths greater than 1500 m. That is why they are the most promising structural
materials for offshore technology in the next century.
This report was presented at the Symposium “Composites for the Next Millennium” in honor of Stephen Tsai's 70th birthday,
Tours, France, 2–3 July, 1999.
Institute of Polymer Mechanics, University of Latvia, Riga, LV-1006 Latvia. Translated from Mekhanika Kompozitnykh Materialov,
Vol. 35, No. 5, pp. 549–560, September–October, 1999. 相似文献
3.
A. A. Skudra 《Mechanics of Composite Materials》1996,32(5):463-466
An empirical approach is proposed for assessing the influence of the synergistic effect on the increase in strength and the
strain limit of a cement matrix at the moment of formation of the first crack.
Riga Technical University, Riga, LV-1047, Latvia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 32, No. 5, pp. 663–667,
September–October, 1996. 相似文献
4.
We show how the Gabriel–Roiter measure, introduced by Ringel in (Bull Sci Math 129:726–748, 2005 and Contemp Math 406:105–135, 2006), applies to indecomposable modules of finite length over right pure semisimple rings, and in particular to the study of
the open problem whether any right pure semisimple ring is of finite representation type.
Dedicated to the memory of Andrey Vladimirovich Roiter. Professor A. V. Roiter has died on 26 July 2006 in Riga, Latvia. He
was born in 1937. 相似文献
5.
The dependence of physical and mechanical properties of monolithic and foamed rigid polyurethanes on the content of flame
retardants was investigated at 293 and 98 K. The character of the influence of the content of trichloroethyl phosphate on
the ultimate tensile elongation and the coefficient of linear thermal expansion for monolithic and foamed polyurethanes at
a temperature of 98 K was established.
Latvian State Institute of Wood Chemistry, Riga, LV-1006 Latvia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 35,
No. 5, pp. 671–676, September–October, 1999. 相似文献
6.
V. A. Polyakov 《Mechanics of Composite Materials》1996,32(5):406-421
A refined model for bending of a three-layered panel with a soft filler is proposed. The modified model permits us to consider
the asymmetry of elastic properties and thickness of the outer layer relative to the middle plane of the panel in a composite
sandwich structure. In constructing the deformation mechanism, a heterogeneous kinematic model was adopted, which, in contrast
to the assumptions for the deformation of the whole stack of layers, features four degrees of displacement freedom permitting
consideration of the separate nature of the deformation of the outer layers in bending and of the intermediate layer in transverse
compression combined with shear. This approach is postulated according to an energetic evaluation of the deformation of the
layers [2]. The specific features of the stress from point forces in cylindrical bending are considered using the operational
Laplace method, which avoids the additional difficulties in analyzing the solution convergence arising when it is represented
by a series of eigenfunctions of the boundary value problem. The fundamental functions of a twelfth-order set of equations
are used to construct the boundary problem reduced to a Cauchy problem. Various boundary effects of the point stress are described
using a generalized Dirac function. Variants are examined for the limiting transformation of the model parameters leading
to a qualitative change in its kinematics and the corresponding simplified bending models.
Institute of Polymer Mechanics, Latvian Academy of Sciences, LV-1006 Riga, Latvia. Translated from Mekhanika Kompozitnykh
Materialov, No. 5, pp. 588–611, September–October, 1996. 相似文献
7.
M. H. B. M. Shariff 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》2009,56(4):1112-1134
A general constitutive theory for anisotropic stress softening in compressible solids is presented. The constitutive equation
describes anisotropic strain induced behaviour of an initially “isotropic” virgin material. Parameters which characterise
damage are proposed together with a concept of damage function. In order to develop an anisotropic stress-softening theory
for compressible materials in close parallel to a recent incompressible anisotropic theory, the right stretch tensor is decomposed
into its isochoric and dilatational parts. The ’free’ energy is expressed as a function of the dilatation, modified principal
stretches, a volume change parameter and invariants of the dyadic products of the principal directions of the right stretch
tensor and two structural tensors. A class of free energy functions is discussed and a special form of this class which satisfies
the Clausius–Duhem inequality is proposed. Results of the theory applied to uniaxial tension, bulk compression and simple
shear deformations are given. A sequence of deformations involving shear, hydrostatic-compression and hydrostatic-tension
deformations is also investigated. In the case of hydrostatic-tension deformation, the stress softening is due to cavitation
damage. The theoretical results obtained are consistent with expected behaviour and compare well with experimental data. 相似文献
8.
J. Plitmanis K. I. Cirule A. F. Kregers A. É. Terauds A. M. Tolks 《Mechanics of Composite Materials》1996,32(5):483-486
The tribological characteristics (wear resistance, coefficient of friction ) of a high-density-polyethylene-base composite
filled with calcite and highly disperse silicon nitride produced by the plasmochemical method are investigated experimentally.
The experiment plan was compiled in the form of a simplex lattice, and new points were planned in conducting the experiments.
Compositions possessing appreciably elevated wear resistance (by a factor of 500) and a coefficient of friction reduced by
20% as compared with the unfilled polymer were obtained.
Institute of Inorganic Chemistry of the Latvian Academy of Sciences, Salasplis, LV-2169. Institute of Polymer Mechanics of
the Latvian Academy of Sciences, Riga, LV-1006. Riga Mechanical University, Riga, LV-1050, Latvia. Translated from Mekhanika
Kompozinykh Materialov, No. 5, pp. 690–695, September–October, 1996. 相似文献
9.
Roberto Andreani Joaquim J. Júdice José Mario Martínez Joao Patrício 《Numerical Algorithms》2011,57(4):457-485
Interior–point algorithms are among the most efficient techniques for solving complementarity problems. In this paper, a procedure
for globalizing interior–point algorithms by using the maximum stepsize is introduced. The algorithm combines exact or inexact
interior–point and projected–gradient search techniques and employs a line–search procedure for the natural merit function
associated with the complementarity problem. For linear problems, the maximum stepsize is shown to be acceptable if the Newton
interior–point search direction is employed. Complementarity and optimization problems are discussed, for which the algorithm
is able to process by either finding a solution or showing that no solution exists. A modification of the algorithm for dealing
with infeasible linear complementarity problems is introduced which, in practice, employs only interior–point search directions.
Computational experiments on the solution of complementarity problems and convex programming problems by the new algorithm
are included. 相似文献
10.
Asymptotic analysis of the behavior of a multichannel queueing system functioning in a Markov medium
The asymptotic behavior of some multidimensional characteristics of two Markov queueing systems, in which an incoming flow
of units and their service time depend on a small parameter ɛ and the state of the Markov medium where these queueing systems
function, is investigated. Bibliography: 6 titles.
Translated fromObchyslyuval’na ta Prykladna Matematyka, No. 76, 1992, pp. 91–98. 相似文献
11.
Gatica Gabriel N.; Meddahi Salim; Oyarzua Ricardo 《IMA Journal of Numerical Analysis》2009,29(1):86-108
12.
A. F. Kregers G. A. Teters Yu. G. Melbardis A. Zh. Lagzdin' 《Mechanics of Composite Materials》1996,32(5):431-438
In a numerical example of compromise optimization by computerized mathematical modeling (2000 realizations) for a known deterministic
solution, in the case of an isotropic spatially reinforced porous composite, certain scatter characteristics of the optimal
solution have been established, namely four standard deviations and six coefficients of linear correlation for four properties—density,
modulus of elasticity, thermal conductivity, and linear thermal expansion coefficient. Of the 17 input data (parameters of
the composite components), 10 are stochastic, the others deterministic. An equation is presented for the four-dimensional
hyperellipsoid of normal distribution with numerical values of the coefficients, as well as all invariants and roots of the
characteristic equation, the matrix of direction cosines of the principal axes of the hyperellipsoid, and the lengths of the
principal semiaxes, depending on the dimensionality of the scattering region and the assigned probability P. The four-dimensional
hyperellipsoid has been projected onto three-dimensional space and then onto a plane. A section of the scattering region has
been constructed.
Institute of Polymer Mechanics, Latvian Academy of Sciences, Riga LV-1006, Latvia. Translated from Mekhanika Kompozitnykh
Materialov, No. 5, pp. 625–635, September–October, 1996. 相似文献
13.
Behavior of concrete cylinders confined by carbon-composite tapes and prestressed yarns 1. Experimental data 总被引:1,自引:0,他引:1
V. Tamuzs R. Tepfers Chi-Sang You T. Rousakis I. Repelis V. Skruls U. Vilks 《Mechanics of Composite Materials》2006,42(1):13-32
The results of a comprehensive test program for the mechanical behavior of round concrete specimens confined by carbon-fiber
epoxy tapes and prestressed carbon yarns are reported. Five different concrete batches of compressive strength from 20 to
100 MPa and the confinement of various thickness and pretension level were investigated. The specimens, which were subjected
to monotonic or repeated compressive loadings, showed a nonlinear stress-strain behavior with a significant ductility and
increased ultimate strength, in contrary to the brittle behavior of plain concrete. The limit of linearity on the stress-strain
diagrams of the confined concrete roughly coincided with the ultimate strength of plain concrete. Above this limit, the damage
accumulation and plastic deformations proceeded in the confined specimens. This fact was evidenced by the increasing slope
of deformation diagrams in unloadings and repeated loadings and by the pronounced residual strains. The limit of linearity
could be raised significantly by pretension of the carbon yarns during their winding.
Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 42, No. 1, pp. 21–44, January–February, 2006. 相似文献
14.
S. Zacks 《Methodology and Computing in Applied Probability》2010,12(4):555-565
Zacks (Failure distribution associated with general renewal damage processes. In: Nikulin M, Commenges D, Haber C (eds) Probability
statistics and modelling in public health. Springer, Berlin, pp 465–475, 2006) studied the reliability function, the hazard function and the distribution of the failure time when a system is subject
to a cumulative, compound renewal damage process. The failure occurs when the damage process crosses a threshold β. In the present paper these results are generalized to the model where the system is replaced after failures. Two cases are
considered: instant replacement and random positive replacement time. The distribution of the age of the current renewal cycle,
as well as its excess life, and the availability function are studied. We derive also the distribution of total time in (0,
t) at which the system has been operational. 相似文献
15.
We consider the direct problem of aeroelectrosounding for a layered medium. The specific feature of this problem is that its
solution is representable as a Bessel transform of a function ƒ of a certain type. We have developed and implemented a method
for fast computation of the Bessel transform of such functions. The method relies on the approximation of ƒ by a linear combination
of exponentials with prespecified exponents. The Bessel transform of the original function ƒ is computed analytically as the
Bessel transform of the approximating linear combination. Numerical computations have been carried out.
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Translated from Prikladnaya Matematika i Informatika, No. 26, pp. 39–48, 2007. 相似文献
16.
Matjaž Konvalinka 《Journal of Algebraic Combinatorics》2012,35(4):519-545
We extend recent results of Assaf and McNamara on a skew Pieri rule and a skew Murnaghan–Nakayama rule to a more general identity,
which gives an elegant expansion of the product of a skew Schur function with a quantum power sum function in terms of skew
Schur functions. We give two proofs, one completely bijective in the spirit of Assaf–McNamara’s original proof, and one via
Lam–Lauve–Sotille’s skew Littlewood–Richardson rule. We end with some conjectures for skew rules for Hall–Littlewood polynomials. 相似文献
17.
Non-monotone trust region methods for nonlinear equality constrained optimization without a penalty function 总被引:3,自引:0,他引:3
We propose and analyze a class of penalty-function-free nonmonotone trust-region methods for nonlinear equality constrained
optimization problems. The algorithmic framework yields global convergence without using a merit function and allows nonmonotonicity
independently for both, the constraint violation and the value of the Lagrangian function. Similar to the Byrd–Omojokun class
of algorithms, each step is composed of a quasi-normal and a tangential step. Both steps are required to satisfy a decrease
condition for their respective trust-region subproblems. The proposed mechanism for accepting steps combines nonmonotone decrease
conditions on the constraint violation and/or the Lagrangian function, which leads to a flexibility and acceptance behavior
comparable to filter-based methods. We establish the global convergence of the method. Furthermore, transition to quadratic
local convergence is proved. Numerical tests are presented that confirm the robustness and efficiency of the approach.
Received: December 14, 2000 / Accepted: August 30, 2001 Published online: September 27, 2002
Key words. nonmonotone trust-region methods – sequential quadratic programming – penalty function – global convergence – equality constraints
– local convergence – large-scale optimization
Mathematics Subject Classification (2000): 65K05, 90C30 相似文献
18.
L. A. Molotkov 《Journal of Mathematical Sciences》2008,148(5):753-759
A special case of a transversely isotropic elastic medium is considered. This medium is excited by a point force perpendicular
to the anisotropy axis. The wave field in this medium is constructed and investigated. The front sets of SV and SH waves are
in contact with one another at a point. In order to investigate a neighborhood of this point, we derive simpler expressions
for the wave field and establish a special function describing the tangency of two front sets. Bibliography: 8 titles.
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Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 342, 2007, pp. 206–216. 相似文献
19.
A nonlinear version of the phenomenological theory of long-term strength of polymer materials (viscoelastic bodies) is proposed.
It is based on the introduction of a function accounting for the damage accumulation connected with changes in the load intensity.
The form of this function may be determined from the results of testing the material with a load changing with time in a certain
way, for instance, periodically. As a parameter, the function contains the rate of the changing load or the frequency for
periodic loads. For a quasi-isotropic material, the basic relationships of the theory proposed are generalized to the case
of combined stresses. The durability (failure time) calculations of the material based on this theory are compared with experimental
data for a number of polymer and composite materials in a wide range of loading modes.
Translated from Mekhanika Kompozitnykh Materialov, Vol. 35, No. 5, pp. 585–594, September–October, 1999. 相似文献
20.
Ya. M. Chabanyuk 《Ukrainian Mathematical Journal》2007,59(9):1441-1452
We obtain sufficient conditions for the stability of a dynamical system in a semi-Markov medium under the conditions of diffusion
approximation by using asymptotic properties of the compensation operator for a semi-Markov process and properties of the
Lyapunov function for an averaged system.
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Translated from Ukrains’kyi Matematychnyi Zhurnal, Vol. 59, No. 9, pp. 1290–1296, September, 2007. 相似文献