Analysis of the film stacking processing parameters for PLLA/flax fibre biocomposites

International audienceNowadays, the market demand for environmentally friendly materials is rapidly increasing. Biodegradable fibres and biodegradable polymers mainly extracted from renewable resources are expected to be a major contribution to the production of new industrial high performance biodegradable composites, partially solving the problem of waste management. At the end of its lifetime, a structural biodegradable composite can be crushed and recycled through a controlled industrial composting process. Bodros et al. [1] showed that biodegradable PLLA (L-polylactide acid)/flax fibres mat composites exhibiting specific tensile properties equivalent to glass fibre polyester composites can be manufactured by an un-optimised film stacking process. In our study, the process has been investigated more extensively. Indeed, the compaction of flax mats requires a higher load than for glass mats of similar areal weight. The transverse permeability of flax mats has also been shown to be lower than for glass mats. In both cases, this is due to a higher degree of entanglement of the flax fibres within the mat. However, the range of permeability and compressibility values of the flax mats are well within the values that allow a good through-thethickness impregnation. Flax fibres cannot sustain long exposures at the impregnation temperature of the mats by PLLA resin. Through-the-thickness impregnation of flax mats processes such as film stacking are more suitable than in-plane impregnation processes such as Resin Transfer Molding because the flow of resin is limited on short distances and allows short times of impregnation

Theoretical and Experimental Modelling of Bubble Formation with Connected Capillaries in Liquid Composite Moulding Processes

The void prediction in LCM processes sparks off interest within the composite material industry because it is a significant issue to keep the expected mechanical properties. The liquid properties, the preform geometry and the flow conditions impact the quantity of void entrapped inside the final product. The complex geometry of the reinforcement due to the arrangement of the bundles and the fibres is a key point to understand and quantify this phenomenon. This paper deals with both simple model networks which can occur inside a fabric representing connected capillaries, so-called "Pore Doublet Model (PDM)". A first is considering two capillaries converging on a node (T-junction) and a second is representing two capillaries interconnected with a supplying principle. These configurations can affect locally the evolution of flow fronts. First, experiments of bubble formed in a T-junction device have been performed and studied. Then a theoretical approach was proposed to forecast microvoid and macrovoid formation, by taking into account a supplying principle and arranged Washburn equation in forced filling.Comment: 8 pages; 11th International Conference Flow Processing in Composite Materials, Auckland : New Zealand (2012

Void Prediction During Liquid Composite Molding Processes: Wetting and Capillary Phenomena

The aim of this work is to contribute in improving fibrous preforms impregnation for Liquid Composite Molding (LCM) processes. The void prediction in LCM sparks off interest within the Composite Material elaboration because it represents a significant issue to keep the expected mechanical properties of the final product. The liquid properties, the preform geometry and the flow conditions impact the void or bubble entrapped inside and outside the yarns. Nevertheless, due to the complex geometry of the reinforcement, experimental characterization of bubble formation remains delicate. Thus, our study deals with two simple model networks representing connected pores so called "Pore Doublet Model". A first is considering two capillaries converging on a node (T-junction) and a second is representing two capillaries interconnected with a supplying principle. In this paper, we emphasize on microfluidic and millifluidic approaches where wetting and capillary forces are significant during bubble formation mechanism.Comment: 8 pages; 15th European Conference on Composite Materials, Venise : Italy (2012

Analytical Modeling of CRTM and RTM Processes. Part II: Applications to the Analysis of the Process

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INFLUENCE OF THE COMPACTION SPEED ON THE TRANSVERSE CONTINUOUS PERMEABILITY

International audienceThe compaction of composite preforms and the flow of resin through the fibrous network take place simultaneously during the Resin Film Infusion process. An experimental device, set up to impose combinations of hydraulic and mechanical loadings (Hydro-Mechanical loadings) to fibrous preforms is used to evaluate the transverse permeability in a continuous manner using different compression speeds for a glass satin weave and a carbon non crimped fabric. The transverse continuous permeability curves of the two fibrous reinforcements evaluated using fast compression speeds are not similar to the ones evaluated using low velocity. The fast compression speed permeability curve is the result of transient phenomena acting on the measured pressure. It therefore reflects the instantaneous permeability behaviour of the reinforcements. This may improve the accuracy of the permeability used to model processes such as RFI where the compression speed is not constant

Analytical Modeling of CRTM and RTM Processes. Part I: General Mathematical Development

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Etude de fibres de lin rouies : comparaison entre la méthode organoleptique et l’analyse thermogravimétrique

International audienceLes fibres végétales sont faites de constituants naturels très sensibles aux conditions environnementales. Dans le cas du lin, par exemple, le rouissage au sol affecte les proportions des constituants de la fibre et donc ses propriétés[1]. Dans l’industrie textile, la qualité des fibres de lin teillé (fibres séparées mécaniquement de la tige après rouissage)est appréciée via une méthodologie d’estimation organoleptique [2]. Cette méthodologie est très pratique et facile à mettre en œuvre,mais l’objectivité et la répétabilité des mesures ne repose que sur l’expertise de l’opérateur...Dans ce travail, la dégradation thermique des constituants des fibres de lin par thermogravimétrie est utilisée pour caractériser un lot non teillé ayant subi différents temps de rouissage(on parle de degré de rouissage). Puis, l’analyse thermogravimétrique est utilisée sur des lots de fibres teillés qui ont été préalablement catégorisés par la méthodologie organoleptique. Un rapprochement de ces deux séries de résultats est entrepris afin de savoir si les évolutions structurales révélées par thermogravimétrie sont corrélées aux paramètres organoleptiques

Numerical simulation of void formation in LCM

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Theoretical calculation of wind (Or water) turbine considering kinetic and potential energy to exceed the Betz limit

The Betz limit sets a theoretical upper limit for the energy efficiency of turbines. The energy efficiency of turbines, expressed as a maximum power coefficient of 16/27. Betz's theory is precise and is based on the calculation of kinetic energy. However, if the potential energy is taken into account the theoretical energy efficiency of a turbine can be higher. Fast wind turbines recover the kinetic energy of the wind in an optimal way. A large amount of potential energy is created without being recovered. The notion of potential energy is fundamental, it is not possible to recover energy, if we do not create a constraint. This article examines this potential energy and the possibility for a wind turbine to transform it into kinetic energy. The Betz theory has been defined from the model of fast moving turbines. This theory has been generalized to slow and fast moving turbines and it has been defined as a law. The conservation of energy implies that if a variation of kinetic energy increases, the variation of potential energy decreases. In the case of slow moving turbines, the conservation of energy applies, but not for the case of fast moving turbines, however this is the reality. This paper proposes a new formulation of the turbine power with a notion of temporal, in order to be able to verify the conservation of energy

Etude de fibres de lin rouies : comparaison entre la méthode organoleptique et l’analyse thermogravimétrique

International audienceLes fibres végétales sont faites de constituants naturels très sensibles aux conditions environnementales. Dans le cas du lin, par exemple, le rouissage au sol affecte les proportions des constituants de la fibre et donc ses propriétés[1]. Dans l’industrie textile, la qualité des fibres de lin teillé (fibres séparées mécaniquement de la tige après rouissage)est appréciée via une méthodologie d’estimation organoleptique [2]. Cette méthodologie est très pratique et facile à mettre en œuvre,mais l’objectivité et la répétabilité des mesures ne repose que sur l’expertise de l’opérateur...Dans ce travail, la dégradation thermique des constituants des fibres de lin par thermogravimétrie est utilisée pour caractériser un lot non teillé ayant subi différents temps de rouissage(on parle de degré de rouissage). Puis, l’analyse thermogravimétrique est utilisée sur des lots de fibres teillés qui ont été préalablement catégorisés par la méthodologie organoleptique. Un rapprochement de ces deux séries de résultats est entrepris afin de savoir si les évolutions structurales révélées par thermogravimétrie sont corrélées aux paramètres organoleptiques