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Lamon J.,CNRS Laboratory for Thermostructural Composites
Composites Science and Technology | Year: 2010

The present paper compares the fragmentation strength distributions predicted using various models including:. -The well-known Monte Carlo simulation method based on chain-of-segments model and fiber strength distribution. This model has been widely used to simulate fragmentation of fibers in polymer or metal matrix.-Fragment dichotomy model based on failures and flaw-strength distributions in successive fragments. This model has been validated in previous papers by comparison to experimental results, and-Bayesian chain-of-elements model based on flaw-strength distribution in the fiber. This model is proposed in this paper.These models are discussed. They were compared to experimental series of fragmentation stresses obtained during tensile tests on SiC matrix composites reinforced with SiC or C fibers. Matrix failures were detected using either acoustic emission counts or SEM inspection during the tests. The influence of preponderant factors was anticipated. © 2010. Source


Marcin L.,ONERA | Maire J.-F.,ONERA | Carrere N.,ONERA | Martin E.,CNRS Laboratory for Thermostructural Composites
International Journal of Damage Mechanics | Year: 2011

The aim of this article is to propose a macroscopic damage model, which describes the nonlinear behavior observed on woven composites with ceramic matrix. The model is built within a thermodynamic framework with internal variables. First of all, the efficiency of the model to describe the mechanical behavior of carbon fiber-reinforced ceramic matrix composites is outlined. Then, the predictive capability of the model is evaluated with the help of an alternate torsion test. © The Author(s), 2010. Source


Vignoles G.L.,CNRS Laboratory for Thermostructural Composites | Ortona A.,CIMSI
International Journal of Thermal Sciences | Year: 2016

Effective thermal conductivities (ETC) under vacuum were computed numerically on 3D blocks of opencell foams either obtained by X-ray tomography or generated by Computer-Aided Design (CAD) with ideal geometries. For the first time a Monte-Carlo/Random Walk code accounting for the coupling of conduction in the solid phase and of radiation in the pore space has been used. The whole range of conduction/radiation ratio, parameterized by a Nusselt number, has been scanned; a law relating the ETC to this parameter has been obtained. In all cases the conductive and radiative contributions are additive. The slope of the radiative contribution to the ETC is found to display a distinct behavior, depending on whether radiation or conduction dominates. The low-temperature regime has an emissivity-dependent ETC slope, while the high-temperature regime does not. The critical ratio between both regimes is related to the ratio between cell and strut diameters. In all cases, it is found that the ETC anisotropy decreases with temperature. Closing some windows enhances conduction parallel to the closing walls and reduces radiation perpendicular to them. This effect is shown to influence the ETC eigendirections in actual media. © 2016 Elsevier Masson SAS. Source


Vignoles G.L.,CNRS Laboratory for Thermostructural Composites
International Journal of Heat and Mass Transfer | Year: 2016

Heat transfer properties from ambient up to extremely high temperatures are a key feature of advanced thermal protection and thermal exchange materials - like ceramic foams or fiber assemblies. Because of their porous nature, heat transfer rests not only on conduction in opaque solids and on convection in pores, but also on radiation trough pores. The precise knowledge of the thermal behavior of these materials in these conditions is an issue. In a "virtual material" framework, we present a computational simulation tool for heat transfer in such materials, combining solid-phase conduction and linearized radiative transfer in open or closed radiating cavities with opaque interfaces. The software is suited to working in large 3D blocks as produced e.g. by X-ray CMT or by image synthesis. An original Monte-Carlo mixed random walks scheme accounting for both diffusion and radiation is presented and validated. The application to a real image of a fibrous medium is described and discussed, principally in terms of the influence of the diffusion/radiation ratio on the effective (large-scale) diffusivity tensor. © 2015 Elsevier Ltd. Source


Reinisch G.,CNRS Laboratory for Thermostructural Composites | Leyssale J.-M.,CNRS Laboratory for Thermostructural Composites | Vignoles G.L.,University of Bordeaux 1
Journal of Chemical Physics | Year: 2010

We present an extension of some popular hindered rotor (HR) models, namely, the one-dimensional HR (1DHR) and the degenerated two-dimensional HR (d2DHR) models, allowing for a simple and accurate treatment of internal rotations. This extension, based on the use of a variable kinetic function in the Hamiltonian instead of a constant reduced moment of inertia, is extremely suitable in the case of rocking/wagging motions involved in dissociation or atom transfer reactions. The variable kinetic function is first introduced in the framework of a classical 1DHR model. Then, an effective temperature and potential dependent constant is proposed in the cases of quantum 1DHR and classical d2DHR models. These methods are finally applied to the atom transfer reaction SiCl3 + BCl3 → SiCl4 + BCl2. We show, for this particular case, that a proper accounting of internal rotations greatly improves the accuracy of thermodynamic and kinetic predictions. Moreover, our results confirm (i) that using a suitably defined kinetic function appears to be very adapted to such problems; (ii) that the separability assumption of independent rotations seems justified; and (iii) that a quantum mechanical treatment is not a substantial improvement with respect to a classical one. © 2010 American Institute of Physics. Source

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