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Pennec F.,GEMH CEC | Alzina A.,GEMH CEC | Nait-Ali B.,GEMH CEC | Tessier-Doyen N.,GEMH CEC | Smith D.S.,GEMH CEC
Computational Materials Science | Year: 2013

In the present paper, a reliability analysis of the effective thermal conductivity of almost fully dense stabilized zirconia ceramics is described. The methodology is used to estimate (i) the probability for the material conductivity value to exceed a critical threshold and (ii) the sensitivity of the effective thermal conductivity to the variability of microstructural heterogeneities. A stochastic model enclosing the probability distributions of microscopic random variables coupled to a heat transfer model was thus established. This approach has been applied to a specific random microstructure exhibiting a highly segregated bimodal distribution of grain sizes and a small pore volume fraction. Due to the complexity of the ceramic microstructure, three representative volume elements were made to depict the ceramic material at different scales. Three-dimensional Voronoï mosaics are used to generate artificial microstructures with a very large number of grains. A computational homogenization method is employed to derive the effective thermal properties of the heterogeneous material for one iteration of random variables. Once the number of iterations achieves a representative sampling of the basic variables, the numerical reliability and sensitivity analysis are carried out. The confidence that can be given to the sensitivity and reliability estimates has been successfully quantified through experimental measurements of thermal diffusivity by the laser flash technique on a series of zirconia samples. © 2011 Elsevier B.V. All rights reserved.

Mathias J.-D.,IRSTEA | Alzina A.,GEMH CEC | Grediac M.,CNRS Pascal Institute | Michaud P.,CNRS Pascal Institute | And 12 more authors.
BioResources | Year: 2015

One of the big global, environmental, and socioeconomic challenges of today is to make a transition from fossil fuels to biomass as a sustainable supply of renewable raw materials for industry. Growing public awareness of the negative environmental effects of petrochemical-based products adds to the need for alternative production chains, especially in materials science. One option lies in the value-added upcycling of agricultural by-products, which are increasingly being used for biocomposite materials in transport and building sector applications. Here, sunflower by-product (obtained by grinding the stems) is considered as a source of natural fibers for engineered biocomposite material. Recent results are shown for the main mechanical properties of sunflower-based biocomposites and the socioeconomic impact of their use. This paper demonstrates that sunflower stem makes a good candidate feedstock for material applications. This is due not only to its physical and chemical properties, but also to its socioeconomic and environmental rationales.

Pennec F.,GEMH CEC | Alzina A.,GEMH CEC | Tessier-Doyen N.,GEMH CEC | Naitali B.,GEMH CEC | Smith D.S.,GEMH CEC
Journal of Physics: Conference Series | Year: 2012

This work is about the calculation of thermal conductivity of insulating building materials made from plant particles. To determine the type of raw materials, the particle sizes or the volume fractions of plant and binder, a tool dedicated to calculate the thermal conductivity of heterogeneous materials has been developped, using the discrete element method to generate the volume element and the finite element method to calculate the homogenized properties. A 3D optical scanner has been used to capture plant particle shapes and convert them into a cluster of discret elements. These aggregates are initially randomly distributed but without any overlap, and then fall down in a container due to the gravity force and collide with neighbour particles according to a velocity Verlet algorithm. Once the RVE is built, the geometry is exported in the open-source Salome-Meca platform to be meshed. The calculation of the effective thermal conductivity of the heterogeneous volume is then performed using a homogenization technique, based on an energy method. To validate the numerical tool, thermal conductivity measurements have been performed on sunflower pith aggregates and on packed beds of the same particles. The experimental values have been compared satisfactorily with a batch of numerical simulations. © Published under licence by IOP Publishing Ltd.

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