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We consider a variational problem infu∈H1(Ω)∫Ω{aϵ&z.sfnc;∇uϵ&z.sfnc;m+g&z.sfnc;uϵ&z.sfnc;m−mfϵuϵ} dx in a bounded domain Ω=F(ϵ)∪M(ϵ) with a microstructure F(ϵ) which is not in general periodic; aϵ=aϵ(x) is of order 1 in F(ϵ) and supx∈M(ϵ)aϵ(x)→0 as ϵ→0. A homogenized model is constructed. To cite this article: L. Pankratov, A. Piatnitski, C. R. Acad. Sci. Paris, Ser. I 334 (2002) 435–440. [Copyright &y& Elsevier]

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For the design and stability analysis of rock structures in underground engineering, a micromechanics-based constitutive model is established in this work to describe the macroscopic mechanical behavior of Fontainebleau quartz sandstone. At the microscopic scale, the Drucker–Prager criterion is adopted to describe the plastic behavior of the solid matrix. The pores are assumed to be spherical and randomly distributed. The influences of porosity and dilatation of the solid phase are fully considered in the elastic behavior with a dilute homogenization scheme and plastic behavior through a macroscopic yield criterion. With the effect of porosity, one finds that the macroscopic tensile and compressive yield strengths of the porous material reduce quickly. By introducing a plastic hardening rule, a macroscopic plastic potential for non-associated flow rule and considering the evolution of porosity, a complete micro–macro constitutive model is constructed and implemented. In addition to the conventional triaxial compression (CTC) test for the study of compressive strength, the tensile strength under the triaxial direct tension (TDT) test is also taken into account by the proposed micro–macro model. The tensile behavior of the studied porous material is quite different from the compressive one. The loading path has a great influence on the porosity evolution. Compared with the experimental data carried out in CTC and TDT tests under different confining pressures, the proposed micromechanics-based model is able to capture the main features of the studied quartz sandstone. [ABSTRACT FROM AUTHOR]

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Copyright of Canadian Journal of Civil Engineering is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The purpose of this paper was to search the relations between the structure of the compressed expanded graphite - polymer - turbostratic carbon composites on successive stages of technological treatment and parameters describing the acoustic emission phenomena in these materials. The acoustic emission method can be used for measurements of changes in the structure and many different properties of materials. These investigations are a continuation of our earlier studies concerning physical, mechanical and chemical properties of porous composites created on the basis of a compressed expanded graphite matrix, obtained after successive technological procedures of impregnation, polymerization and carbonization of polyfurfuryl alcohol. The aim of this work was to investigate materials obtained at different levels of technological processing, thus with different densities, porosity, physical and chemical properties, by using the acoustic emission method. In compressed expanded graphite composites structures one can differentiate two basic directions: perpendicular to the bedding plane of graphite flakes and parallel to this one. The all presented results were obtained for the uniaxial strain applied in the direction perpendicular to the bedding plane of the composite structure. Analysis of acoustic emission parameters provides information on physical and chemical processes in these materials. [ABSTRACT FROM AUTHOR]

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Since the decalcification of cement paste has been largely reviewed, we focus our studies on the influence of aggregate nature on this phenomenon in relation to the type of cement used, Ordinary Portland Cement or blended cement with fly ash and slag. Some characteristics of similar mortar mixtures where only aggregate nature differs (lime and siliceous sand) are therefore compared for the two types of cement before and after chemical decalcification induced by ammonium nitrate attack: mechanical strength, microstructure (porosity observed by mercury intrusion and profiles of oxide content trough degraded and sound zones determined by electronic microprobe analysis), transport properties (chloride ions diffusivity, gas and water permeabilities). The characterization of sound mortars underlines that siliceous aggregates promote less porous cementitious matrix. The duplication of ammonium nitrate attacks on same material allows testing the experimental parameters governing the degradation. The flows of calcium leached, the microstructure and the evolution of transport properties with decalcification suggest that limestone aggregates are not inert material. Consequently, for the mortars incorporating siliceous sand, the cementitious matrix is more decalcified and this leads to an amplification of ionic transports, especially through blended cement paste. [ABSTRACT FROM AUTHOR]

The influence of fabric on mechanical behaviour is explicitly considered in some of the current constitutive models for unsaturated soils. These are based on assumptions regarding the interaction between different levels of structure, which still require experimental validation. A study has been carried out to investigate the evolution of fabric in a compacted natural clay during wetting and loading, and the results are presented in this paper. Samples of London Clay were statically compacted to the same initial conditions, dry of optimum moisture content in a Proctor plot, and subsequently taken along complex stress paths involving wetting, loading, or a combination of both. Mercury intrusion porosimetry (MIP) and environmental scanning electron microscopy (ESEM) microstructure investigations were carried out to observe and quantify the change in fabric associated with each path. The soil fabric was observed to change from an aggregate to a matrix type structure along all wetting paths. This transition was found to take place only when the suction was reduced to a value close to zero kPa. Results also showed that fabric changes during yielding were stress path-dependent. It was not possible to find a correspondence between the volume of free porosity and the volume of intra-aggregate pores, as suggested by some authors. Finally, the volume of pore water was found to agree closely with the volume of intra-aggregate pores, providing support to the assumption that in an unsaturated aggregate microstructure the clay aggregations are saturated. [ABSTRACT FROM AUTHOR]

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Copyright of Géotechnique is the property of Thomas Telford Ltd and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)