3D MORPHOLOGICAL MODELLING OF A RANDOM FIBROUS NETWORK

In the framework of the Silent Wall ANR project, the CMM and the US2B are associated in order to characterize and to model fibrous media studying 3D images acquired with an X-Ray tomograph used by the US2B. The device can make 3D images of maximal 23043 voxels with resolutions in the range of 2 μm to 15 μm. Using mathematical morphology, measurements on the 3D X-Ray CT images are used to characterize materials. For example measuring the covariance on these images of an acoustic insulating material made of wooden fibres highlights the isotropy of the fibres orientations in the longitudinal planes which are perpendicular to the compression Oz axis. Moreover, it is possible to extract other morphological properties from these image processing methods such as the size distribution either of the fibres or of the pores by estimating the morphological opening granulometry of the considered medium. Using the theory of random sets introduced by Georges Matheron in the early 1970's, the aim of this work is to model such a fibrous material by parametric random media in 3D according to the prior knowledge of its morphological properties (covariance, porosity, size distributions, etc.). A Boolean model of random cylinders in 3D stacked in planes parallel to each other and perpendicular to the Oz compression axis is first considered. The granulometry results provide gamma distributions for the radii of the fibres. In addition, a uniform distribution of the orientations is chosen, according to the experimental isotropy measurements in the longitudinal planes. Finally the third statistical factor is the length distribution of the fibres which can be fitted by an exponential distribution. Thus it is possible to estimate the validity of this model first by trying to fit the experimental transverse and longitudinal covariances of the pores with the theoretical ones taking into account the statistical distributions of the dimensions of the random cylinders. The second method to validate the model consists in comparing morphological measurements (density profiles, covariance, opening granulometry, tortuosity, specific surface area) processed on real and on simulated media

Microstructure et propriétés mécaniques de matériaux isolants à base de fibres de bois

On s’intéresse au comportement mécanique en compression des isolants thermiques à base de fibres de bois utilisés dans le bâtiment, de très forte porosité, élaborés par un procédé textile non tissé. Les états de la structure d'un panneau soumis à une sollicitation de compression transverse (33% et 73%) ont été suivsi en 3D par microtomographie X. Le comportement particulier mis en lumière par l'accès à la densification locale est relié à la très faible densité du matériau. En particulier, les fibres de bois ne sont pas individuellement mécaniquement comprimées et la déformation macroscopique du matériau n'engendre que leur réorganisation spatiale. Ces résultats sont mis en relation avec des caractéristiques morphologiques de structures évaluées par analyse d'image 3D.We focus on the mechanical behaviour of a thermal insulating panel made of wood fibres. The making process is a non-woven fabric process that generates a high porosity and a very low-density material. The 3D internal structure of a compressed (33% and 73%) insulating panel was followed by X-ray microtomography. The special behaviour is linked to the low-density structure of the panel. In particular, the fibres are not compressed and the macroscopic deformation of the sample only generates a new organisation of the fibres in the panel. These results are confirmed by morphological measurements that were performed by 3D image analysis

3D structural characterisation and deformation measurements of wood-based fibrous insulators under compression

Communication écrite + Posterabsen

Caractérisation microstructurale 3D et densification locale d'isolants fibreux cellulosiques sollicités en compression

International audienceIn this work, we focus on a thermal insulating panel made of wood fibres. The making process is a non-woven fabric process that generates a high porosity and a very lowdensity material. Thermal properties were first investigated. This paper deals with mechanical properties that are involved in the production line, transport and handling in the construction site. An insulating panel was compressed (33% and 73%) and we followed insitu its internal deformation using X-ray microtomography. The results enlighten a special behaviour that is linked to the low-density structure of the panel. In particular, the fibres are not compressed and the macroscopic deformation of the sample generates only a new organisation of the fibres in the panel. These results are confirmed by morphological measurements that were performed by 3D image analysis.On s'intéresse à des isolants thermiques à base de fibres de bois utilisés dans le bâtiment, de très forte porosité, élaborés par un procédé textile non tissé. Les propriétés thermiques ont fait l'objet des premières études et les propriétés mécaniques, intervenant lors du transport et de la manipulation, font l'objet de ce travail. Nous avons suivi in situ, grâce à la microtomographie X, les états de déformation interne d'un panneau d'isolation soumis à une sollicitation de compression transverse (33 % et 73 %). Le comportement particulier mis en lumière par l'accès à la déformation locale est relié à la très faible densité du matériau. En particulier, les fibres de bois ne sont pas individuellement mécaniquement comprimées et la déformation macroscopique du matériau n'engendre que leur réorganisation spatiale. Ces résultats sont mis en relation avec des caractéristiques morphologiques de structures évaluées par analyse d'image 3D

3D morphological characterization, modeling of fibrous media

International audienc

3D morphological characterization of phonic insulation fibrous media

International audienceIn the framework of the Silent Wall ANR project, the CMM and the US2B are associated in order to characterize and to model fibrous media studying 3D images acquired with an X-Ray microtomograph used by the US2B. The device can make 3D images of maximal size 2304 3 voxels with resolutions in the range of 2-15 μm. Using mathematical morphology, measurements on the 3D X-Ray CT images are performed to characterize materials. For example, measuring the covariance on these images of an acoustic insulating material made of wooden fibers highlights the transverse isotropy of the fibers orientations in the xOy planes perpendicular to the compression Oz axis. Moreover, it is possible to extract other morphological properties, such as the size distribution either of the fibers or of the pores by estimating the morphological opening granulometry of the considered medium. Finally the morphological tortuosity of the fibrous and porous networks are estimated from geodesic propagations. The tortuosity is a parameter which can help to link physical, acoustic, and morphological properties of the material. Moreover the effects of the boundary layer, where viscous and thermal damping of the sound take place, are studied from the point of view of the tortuosity

Modèle booléen 3D de cylindres aléatoires renseigné par des images microtomographiques de matériaux fibreux

National audienc

Design of a thermal and sound insulating board. From the concept to the realisation

Cet article s’appuie sur les travaux réalisés dans le cadre de deux programmes soutenus par l’ANR, l’un concerne le développement de méthodes d’éco-conception, le second porte sur la conception de matériaux thermo-acoustiques pour le bâtiment. La démarche est basée sur l’utilisation de ressources d’origine agricole à caractère abondant, renouvelable et non concurrentiel d’utilisations alimentaires, d’une part, et l’optimisation des performances par les principes de conception (multimatériaux retenus, mode d’assemblage, introduction d’hétérogénéités maîtrisées), d’autre part. Les performances attendues se basent sur les NRT et NRA 2010, avec comme référence les produits commercialisés les plus courants. Après une présentation détaillée des données du problème de conception – connaissances disponibles – quelques éléments de choix sont proposés. L’aspect procédé est brièvement abordé en fin d’article.This paper relies on the work realised within the framework of 2 ANR projects, the first one concerning the development of eco-design tools, and the second treating a potential application to the design of sound insulating materials for building applications. The approach is based on the utilisation of agro resources having the character of being abundant, renewable, and non concurrent with food uses, on one hand, and the optimisation of performances by design principles, on the other hand (homogeneous or layered systems, introduction of heterogeneities). The expected performances are those of NRA 2010, with the most usual commercialised products as reference materials. After a detailed presentation of the available knowledge (and the corresponding gaps), some elements of choice are presented

Model predictive control of a thermally activated building system to improve energy management of an experimental building: Part II - Potential of predictive strategy

Thermally Activated Building Systems (TABS) are difficult to control due to the time lag between the con- trol sending and the response of the indoor temperature. Energy management of systems having such a high inertia can be improved by optimizing the restart time thanks to both occupancy and weather antic- ipation. Predictive control is suitable for systems with numerous constrained inputs and outputs whose objective function varies over time such as buildings with intermittent occupancy. This work proposes to use a Model Predictive Control (MPC) for one TABS in particular: a floor heating system (FHS) of an experimental building. Conventional control techniques and a state of the art on the predictive control of FHS are presented. A complete control loop (sensor, actuator, controller) was implemented on an experi- mental room. The predictive controller that integrate the model selected in Part I is compared with two conventional control strategies. The energy saving potential of the predictive controller is confirmed by both local experimentation and simulation on three climates. The energy saving is close to 40% over the whole heating season with an improved or equivalent comfort situation compared to the other two ref- erence strategies. The absolute gain is constant over the heating period but the most significant relative gains are obtained in the mid-season