Boundary-layer effects on the effective response of fibre-reinforced media are analysed. The distribution of the fibres is assumed random. A methodology is presented for obtaining non-local effective constitutive oper...
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Boundary-layer effects on the effective response of fibre-reinforced media are analysed. The distribution of the fibres is assumed random. A methodology is presented for obtaining non-local effective constitutive operators in the vicinity of a boundary. These relate ensemble averaged stress to ensemble averaged strain. Operators are also developed which re-construct the local fields from their ensemble averages. These require information on the local configuration of the medium. Complete information is likely not to be available, but averages of these operators conditional upon any given local information generate corresponding conditional averages of the fields. Explicit implementation is performed within the framework of an approximation of Hashin-Shtrikman type. Two types of geometry are considered in examples: a half-space and a crack in an infinite heterogeneous medium. These are representative, asymptotically, of the field in the vicinity of any smooth boundary, and in the vicinity of a crack tip, respectively. Results have been obtained for the case of anti-plane deformation, realized by the imposition of either Dirichlet or Neumann conditions on the boundary;those for the Neumann condition are presented and discussed explicitly. The stresses in both fibre and matrix adjacent to a crack tip are shown to differ substantially from the values that would be predicted by ordinary homogenization. (C) 2003 Elsevier Science Ltd. All rights reserved.
Most cellular solids are random materials, while practically all theoretical structure-property relations are for periodic models. To generate theoretical results for random models the finite element method (FEM) was ...
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Most cellular solids are random materials, while practically all theoretical structure-property relations are for periodic models. To generate theoretical results for random models the finite element method (FEM) was used to study the elastic properties of open-cell solids. We have computed the density (rho) and microstructure dependence of the Young's modulus (E) and Poisson's ratio (nu) for four different isotropic random models. The models were based on Voronoi tessellations, level-cut Gaussian random fields, and nearest neighbour node-bond rules. These models were chosen to broadly represent the structure of foamed solids and other (non-foamed) cellular materials. At low densities, the Young's modulus can be described by the relation E proportional to rho (n). The exponent n and constant of proportionality depend on microstructure. We find 1.3 < n < 3, indicating a more complex dependence than indicated by periodic cell theories, which predict n = 1 or 2. The observed variance in the exponent was found to be consistent with experimental data. At low densities we found that nu approximate to 0.25 for three of the four models studied. In contrast, the Voronoi tessellation, which is a common model of foams, became approximately incompressible (nu approximate to 0.5), This behaviour is not commonly observed experimentally. Our studies showed the result was robust to polydispersity and that a relatively large number (15%) of the bonds must be broken to significantly reduce the low-density Poission's ratio to nu approximate to 0.33. (C) 2001 Elsevier Science Ltd. All rights reserved.
作者：
Denoual, CHild, FUniv Paris 06
CNRS LMT Cachan ENS Cachan F-94235 Cachan France CTA
Dept Mat Surfaces Protec DGA F-94114 Arcueil France
Modeling dynamic fragmentation of brittle materials usually implies to choose between a discrete description of the number of fragments and a continuum approach with damage variables. A damage model that can be used i...
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Modeling dynamic fragmentation of brittle materials usually implies to choose between a discrete description of the number of fragments and a continuum approach with damage variables. A damage model that can be used in the whole range of loadings (from quasi-static to dynamic ones) is developed. The deterministic or probabilistic nature of fragmentation is discussed. Qualitative and quantitative validations are given by using a real-time visualization configuration for analyzing the degradation kinetics during impact and a moire technique to measure the strains in a ceramic tile during impact. Finally, a closed-form solution of the change of the number of broken defects with the applied stress gives a way of optimizing the microstructure of ceramics for armor applications. (C) 2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved.
The full experimental assessment of an automatic polarisation mode dispersion (PMD) compensator at 40 Gbit/s over realistic PMD statistics is reported. Results, consolidated by numerical simulations, show that the PMD...
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The full experimental assessment of an automatic polarisation mode dispersion (PMD) compensator at 40 Gbit/s over realistic PMD statistics is reported. Results, consolidated by numerical simulations, show that the PMD limit is increased twofold with the compensator.
We present a novel multi-resolution point sample rendering algorithm for keyframe animations. The algorithm accepts triangle meshes of arbitrary topology as input which are animated by specifying different sets of ver...
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We present a novel multi-resolution point sample rendering algorithm for keyframe animations. The algorithm accepts triangle meshes of arbitrary topology as input which are animated by specifying different sets of vertices at keyframe positions. A multi-resolution representation consisting of prefiltered point samples and triangles is built to represent the animated mesh at different levels of detail. We introduce a novel sampling and stratification algorithm to efficiently generate suitable point sample sets,for moving triangle meshes. Experimental results demonstrate that the new data structure can be used to render highly complex keyframe animations like crowd scenes in real-time.
The non-local constitutive behaviour of an infinite composite laminate is analyzed. The laminate is treated as random and is subjected to a combination of deterministic and configuration-dependent body force. In this ...
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The non-local constitutive behaviour of an infinite composite laminate is analyzed. The laminate is treated as random and is subjected to a combination of deterministic and configuration-dependent body force. In this case, in addition to the effective non-local elastic operator, other non-local constitutive operators must be considered in order to define the mean response of the body. For a laminate subjected to forces that vary only in the direction of lamination, these operators are obtained explicitly. The Hashin-Shtrikman principles developed by Luciano and Willis (Luciano, R., Willis, J,R., 2001a. Bounds on non-local effective relations for random composites loaded by configuration-dependent body force, to appear in J. Mech. Phys. Solids), which provide bounds for the operators for general composites, are shown to generate exactly the two operators that define the stress, while giving only bounds for the remaining operator that appears in the expression for the total energy. The case of a two-phase laminate with the layers arranged periodically is presented as an example. (C) 2001 Elsevier Science Ltd. All rights reserved.
1.52Tbit/s OCDM/WDM (4 OCDM x 19 WDM x 20Gbit/s) transmission based on simultaneous multi-wavelength optical encoding of a single supercontinuum sourer is experimentally demonstrated with 0.4 bit/s/Hz spectrum efficie...
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1.52Tbit/s OCDM/WDM (4 OCDM x 19 WDM x 20Gbit/s) transmission based on simultaneous multi-wavelength optical encoding of a single supercontinuum sourer is experimentally demonstrated with 0.4 bit/s/Hz spectrum efficiency.
This paper focuses on the application of statistical continuum mechanics to the prediction of mechanical response of polycrystalline materials and microstructure evolution under large plastic deformations. A statistic...
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This paper focuses on the application of statistical continuum mechanics to the prediction of mechanical response of polycrystalline materials and microstructure evolution under large plastic deformations. A statistical continuum mechanics formulation is developed by applying a Green's function solution to the equations of stress equilibrium in an infinite domain. The distribution and morphology of grains (crystals) in polycrystalline materials is represented by a set of correlation functions that are described by the corresponding probability functions. The elastic deformation is neglected and a viscoplastic power law is employed for crystallographic slip in single crystals. In this formulation, two- and three-point probability functions are used. A secant modulus-based formulation is used. The statistical analysis is applied to simulate homogeneous deformation processes under uniaxial tension, uniaxial compression and plane strain compression of an FCC polycrystal. The results are compared to the well-known Taylor upper bound model and discussed in comparison to experimental observations. (C) 2001 Elsevier Science Ltd. All rights reserved.
In this paper, fibre-reinforced media are analysed. The distribution of the fibres is assumed random. A combination of deterministic and configuration-dependent body forces is considered. In this case, several non-loc...
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In this paper, fibre-reinforced media are analysed. The distribution of the fibres is assumed random. A combination of deterministic and configuration-dependent body forces is considered. In this case, several non-local effective constitutive operators must be taken into account in order to define the mean response of the material. For two phase composites, expressions for all these operators have been obtained and in the case of fibre-reinforced materials Hashin-Shtrikman type bounds are explicitly developed in the real and the Fourier space, Finally, a periodic distribution of fibres is studied as an example. (C) 2001 Elsevier Science Ltd. All rights reserved.
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