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Mareau C.,Arts et Metiers ParisTech | Berbenni S.,CNRS Study of Microstructures, Mechanics and Material Sciences lab
International Journal of Plasticity

The modeling of heterogeneous materials with an elasto-viscoplastic behavior is generally complex because of the differential nature of the local constitutive law. Indeed, the resolution of the heterogeneous problem involves space-time couplings which are generally difficult to estimate. In the present paper, a new homogenization model based on an affine linearization of the viscoplastic flow rule is proposed. First, the heterogeneous problem is written in the form of an integral equation. The purely thermoelastic and purely viscoplastic heterogeneous problems are solved independently using the self-consistent approximation. Using translated field techniques, the solutions of the above problems are combined to obtain the final self-consistent formulation. Then, some applications concerning twophase fiber-reinforced composites and polycrystalline materials are presented. When compared to the reference solutions obtained from a FFT spectral method, a good description of the overall response of heterogeneous materials is obtained with the proposed model even when the viscoplastic flow rule is highly non-linear. Thanks to this approach, which is entirely formulated in the real-time space, the present model can be used for studying the response of heterogeneous materials submitted to complex thermo-mechanical loading paths with a good numerical efficiency. © 2014 Elsevier Ltd. All rights reserved. Source

Forquin P.,CNRS Study of Microstructures, Mechanics and Material Sciences lab
European Physical Journal: Special Topics

In the present work, an experimental method named "the rocking spalling test" is proposed to investigate the crack-propagation velocity in concrete and rock-like materials under dynamic tensile loading. This method is based on the use of double-notched specimens loaded in spalling tests. A compressive pulse is transmitted to a rectangular specimen by means of a Hopkinson bar. It is reflected as a tensile wave on the opposite free surface of the sample. A large notch provides a rocking effect of the rear part of the specimen whereas a short notch is used to trigger a single unstable crack. This experimental configuration has been optimized through a series of numerical simulations. Finally, a series of tests have been conducted on dry and wet concrete specimens. Crack gauges and ultra-high speed camera coupled to Digital Image Correlation have been used to characterize the crack speed in dry and wet concrete samples. © 2012 EDP Sciences and Springer. Source

Hattab M.,CNRS Study of Microstructures, Mechanics and Material Sciences lab
Comptes Rendus - Mecanique

The aim of the experimental study was to identify the local deformation properties in a clayey material which can be activated at the macroscopic ultimate state known by critical state. The approach consists of an extensive study, based on a Scanning Electron Microscope (SEM) picture analysis, of the orientation of the clay particles characterized in the last stages of triaxial loading. © 2011 Académie des sciences. Source

Charpentier I.,CNRS Study of Microstructures, Mechanics and Material Sciences lab
Optimization Methods and Software

Modelling often involves nonlinear parametric problems and bifurcation analysis. This interdisciplinary paper reviews higher-order numerical methods for the solution of nonlinear problems, and proposes a synthesis of two different conceptual frameworks, namely automatic differentiation and the asymptotic numerical method. Various mechanical problems and references illustrate the presentation. © 2012 Taylor & Francis. Source

Gu C.F.,Monash University | Toth L.S.,CNRS Study of Microstructures, Mechanics and Material Sciences lab
Acta Materialia

Numerical simulations of texture development in polycrystalline oxygen-free high conductivity (OFHC) copper have been studied using the Taylor, viscoplastic self-consistent (VPSC) and a recent Taylor type polycrystal grain refinement (GR) model for the forward and reverse strain conditions. The predictions were compared with each other and with experimental results. OFHC copper was deformed by equal channel angular pressing (ECAP) for up to two passes in Route C. In this Route the deformation mode is shear and is reversed every second pass, however, shear texture is still observed experimentally. For this reason this case is suitable to test the predictive capacity of polycrystal models. The simulation results demonstrate that the magnitude of the shear strain increment plays an important role in predicting texture evolution during strain reversal. If the strain increment is large the three models predict a strain reversal shear texture in acceptable agreement with the experimental results. However, when the strain increments are sufficiently small (as they should be to obtain high precision), both the Taylor and VPSC models return the texture to its initial state; only the GR model can produce a strain reversal texture in accord with the experimental results. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Source

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