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Shen W.Q.,Lille Laboratory of Mechanics | Shao J.F.,Lille Laboratory of Mechanics | Dormieux L.,CNRS Navier Laboratory | Kondo D.,University Pierre and Marie Curie
Computational Materials Science | Year: 2012

In the framework of limit analysis theory, we derive closed-form expressions of approximate criteria for ductile porous materials whose plastically compressible matrix obeys to an elliptic criterion. The general methodology is based on limit analysis of a hollow sphere subjected to a uniform strain rate boundary conditions. We first consider a porous medium with a Green type matrix and establish the corresponding macroscopic yield function. Then, the obtained results are used in order to investigate double porous materials whose solid phase at the microscale (the smallest scale) obeys a von Mises criterion. The results are assessed by comparing them with numerical data, and with recently published results. © 2012 Elsevier B.V. All rights reserved. Source

Pouya A.,CNRS Navier Laboratory
Advances in Water Resources | Year: 2012

Governing equations for flow in three-dimensional heterogeneous and anisotropic porous media containing fractures or cracks with infinite transverse permeability are described. Fractures are modeled as zero thickness curve surfaces with the possibility of multiple intersections. It is assumed that flow obeys to an anisotropic Darcy's law in the porous matrix and to a Poiseuille type law in fractures. The mass exchange relations at fractures intersections are carefully investigated as to establish a complete mathematical formulation for the flow problem in a fractured porous body. A general potential solution, based on singular integral equations, is established for steady state flow in an infinite fractured body with uniform and isotropic matrix permeability. The main unknown variable in the equations is the pressure field on the crack surfaces, reducing thus from three to two the dimension of the numerical problem. A general transformation lemma is then given that allows extending the solution to matrices with anisotropic permeability. The results lead to a simple and efficient numerical method for modeling flow in three-dimensional fractured porous bodies. © 2011 Elsevier Ltd. Source

Shen W.Q.,Lille Laboratory of Mechanics | Kondo D.,CNRS Jean Le Rond dAlembert Institute | Dormieux L.,CNRS Navier Laboratory | Shao J.F.,Lille Laboratory of Mechanics
Mechanics of Materials | Year: 2013

The present paper is devoted to a micro-macro model of plastic deformation in Callovo Oxfordian argillite. This material is composed of a porous clay matrix which is reinforced by linear elastic mineral grains. The clay matrix is itself constituted of a solid phase containing a distribution of pores. The solid phase of clay matrix is described by a pressure sensitive plastic model. By means of a two step homogenization procedure, a macroscopic plastic criterion is formulated to estimate the nonlinear behavior of the clayey rock taking into account influences of pores and of mineral inclusions. Both associated and non-associated macroscopic plastic flow rules depending if the solid phase is associated or not. The mechanical behavior of the clayey rock in conventional triaxial compression tests is studied with the proposed micro-macro model. It is shown that the non-associated plastic flow rule of the solid phase is an essential mechanism for the description of the macroscopic plastic deformation of the clayey rock. Comparisons between the predicted results and experimental data show that the proposed model is able to capture the main features of the mechanical behavior of the studied material.© 2012 Elsevier Ltd. All rights reserved. Source

Roussel N.,CNRS Navier Laboratory
Kuei Suan Jen Hsueh Pao/Journal of the Chinese Ceramic Society | Year: 2015

By going through rational and micro-mechanical arguments on particle/particle and particle/fluid interactions, we first provide here a conceptual diagram of predominant interactions within flowing cement pastes under simple shear in steady state as a function of shear rate and solid volume fraction. Within this frame, we then focus on the last four years advances in the understanding of the main changes in the underlying physics occurring when the most common polymers used in the cement construction industry are added to a cement suspension. We finally discuss the upscaling between cement paste rheology and concrete fresh properties. © 2015, Chinese Ceramic Society. All right reserved. Source

Bleyer J.,CNRS Navier Laboratory | De Buhan P.,CNRS Navier Laboratory
European Journal of Mechanics, A/Solids | Year: 2016

This work investigates the formulation of lower and upper bound finite elements for the yield design (or limit analysis) of shell structures. The shell geometry is first discretized into triangular planar facets so that previously developed lower bound equilibrium and upper bound kinematic plate finite elements can be coupled to membrane elements. The other main novelty of this paper relies on the formulation of generalized strength criteria for shells in membrane-bending interaction via an implicit upscaling procedure. This formulation provides a natural strategy for constructing lower and upper bound approximations of the exact shell strength criterion and are particularly well suited for a numerical implementation using second-order cone programming tools. By combining these approximate strength criteria to the previously mentioned finite elements, rigorous lower and upper bound ultimate load estimates for shell structures can be computed very efficiently. Different numerical examples illustrate the accuracy as well as the generality and versatility of the proposed approach. © 2016 Elsevier Masson SAS. All rights reserved. Source

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