A P1/P1 Finite Element Framework for Taking Into Account Capillary Effects in Biphasic Flow Simulations

This work describes a computational strategy, based on a stabilised finite element method, to simulate bifluid flow with capillary effects in a fibrous microstructure. In this framework, triple junction equilibrium is imposed as a natural condition in the weak formulation of the Stokes problem. Two types of 2D microstructures are then considered, hexagonal and random, and studied in terms of numerical permeability and capillary pressure

Capillary wicking in flax fabrics - Effects of swelling in water

International audienceIn this study, wicking in flax fabrics was investigated through an experimental method coupled with Washburn theory. This method was previously shown effective for carbon fabrics (Pucci et al. [21]) to determine morphological characteristics and apparent advancing contact angles. For natural fibers, Washburn equation is not sufficient to describe wicking because of moisture sorption that causes fiber swelling during liquid imbibition. Some flax fabrics were submitted to a thermal treatment known to modify fibers chemistry. Wicking tests with water were performed on both fabrics at different fiber volume ratios. It was observed that wicking trend is very different for these two types of reinforcements: treated fabrics show typical linear trends described by Washburn equation, while untreated flax fabrics lose linearity during wicking. Sorption tests performed on elementary fibers proved that swelling is less significant for treated flax fibers. A model was proposed and was shown to describe properly wicking in natural fabrics undergoing swelling

Tensiometric method to reliably assess wetting properties of single fibers with resins: Validation on cellulosic reinforcements for composites

International audienceWetting properties and capillary parameters are of first interest for composite and especially biocomposite manufacturing, interface compatibility between reinforcement and matrix, and durability. Few studies have been dedicated in literature to continuous textile fibers and uncured liquid resins wetting properties, and particularly the methods used may be ambiguous, revealing a wide dispersion in results. In this work a reliable method is proposed to determine properly the wetting properties of fibers and some resins commonly used for composite applications. Firstly, a procedure to characterize dispersive and polar components of surface tension for an epoxy and a partially bio-based resin with a tensiometer is proposed. Then a new method was applied on single fibers of semi-synthetic cellulose (viscose), which allows deriving representative values of contact angles from a series of measurements, minimizing the measurement scatter even when using a conventional tensiometer. Resin components and contact angles between cellulose fibers and test liquids, including resins, led to characterize dispersive and polar components of fiber surface energy

Wicking Tests for Unidirectional Fabrics: Measurements of Capillary Parameters to Evaluate Capillary Pressure in Liquid Composite Molding Processes

International audienceDuring impregnation of a fibrous reinforcement in liquid composite molding (LCM) processes, capillary effects have to be understood in order to identify their influence on void formation in composite parts. Wicking in a fibrous medium described by the Washburn equation was considered equivalent to a flow under the effect of capillary pressure according to the Darcy law. Experimental tests for the characterization of wicking were conducted with both carbon and flax fiber reinforcement. Quasi-unidirectional fabrics were then tested by means of a tensiometer to determine the morphological and wetting parameters along the fiber direction. The procedure was shown to be promising when the morphology of the fabric is unchanged during capillary wicking. In the case of carbon fabrics, the capillary pressure can be calculated. Flax fibers are sensitive to moisture sorption and swell in water. This phenomenon has to be taken into account to assess the wetting parameters. In order to make fibers less sensitive to water sorption, a thermal treatment was carried out on flax reinforcements. This treatment enhances fiber morphological stability and prevents swelling in water. It was shown that treated fabrics have a linear wicking trend similar to those found in carbon fabrics, allowing for the determination of capillary pressure

Capillary wicking in a fibrous reinforcement - Orthotropic issues to determine the capillary pressure components

International audienceCapillary pressure effect is one of the most critical issues to understand void formation mechanisms in LCM processes. However characterisation of capillary pressure exhibits complex phenomena controlling directional flow at several scales of observation. In the present study a new definition of capillary pressure PcapPcap and an experimental technique to determine it are described. Wicking tests at the scale of the fabric have been carried out with a tensiometric technique. A good agreement with the Washburn equation has been shown and an equivalence with Darcy law has been proposed. This technique was extended to the measurement of capillary pressure in the three principal directions on a classical quasi-UD carbon fabric. This first approach performed with test liquids (water), will be conducted on other reinforcements and fluids to be more relevant with the final application: LCM processes

Capillary pressure contribution in fabrics as a function of fibre volume fraction for Liquid Composite Moulding processes

International audienceLiquid Composite Moulding processes are considered as promising and effective to manufacture structure composite parts reinforced with synthetic and natural fabrics. The main novelty of this work is the estimation of capillary pressure (Pcap) for both fabrics at different fibre volume fractions (Vf) and with different liquids. From the previous works, the Pcap was defined as the equivalence between Washburn’s equation and Darcy’s law while our novel model for the capillary wicking could predict very well the swelling behaviour of natural fabrics. The combination of our Pcap definition and our novel model was explored in this study. Linear trends, thresholds and extremums of Pcap at different conditions were found for the first time. These results are relevant to estimate the importance of capillary effects during Liquid Composite Moulding processes and extremely valuable for numerical models at the fibrous scale to predict voids formation

Resin infusion-based processes simulation : coupled Stokes-Darcy flows in orthotropic preforms undergoing finite strain

International audienceThe aim of this paper is to present an overall model for the study of resin infusion based processes, in particular, the impregnation of a liquid resin through dry deformable fibrous reinforcements. This model can be appliedto a wide range of activities in many fields of engineering. Here, our approach based on a monolithic formulation in a level-set framework allows to strongly couple a Stokes-Darcy flow in low permeability media undergoing finite strains. The Stokes-Darcy coupled problem is solved using a mixed velocity-pressure formulation stabilized by a multi-scale method. A key feature of our approach is the fluid-solid interaction leading to couple a fluid/porous flow to a non-linear solid mechanics formulation. The interaction phenomenon due to the resin flow in the orthotropic highly compressible preform is based on both Terzaghi's law and on explicit relation expressing permeability as function of porosity in finite strains mechanical framework. Finally, simulations of industrial design parts are performed to illustrate the abilities of our approach and the relevance of this fluid/porous-solid mechanics coupled problem for composite material process simulations

Simulation numérique des phénomènes capillaires et de mouillage pour l'étude de la formation de macro/micro-porosités dans les procédés d'élaboration par infusion

International audienceCet article présente une stratégie numérique, basée sur une approche éléments finis pour la simulation du contact entre deux fluides et un solide, impliquant des effets capillaires et de mouillage, appliquée à la formation de macro/micro-porosités au cours des procédés d'élaboration des matériaux composites par infusion. Ce modèle s'appuie sur une description eulérienne des deux fluides non miscibles (la résine et l'air) avec des conditions aux bords qui décrivent les phénomènes de mouillage aux interfaces fluides/fibres. L'interface entre les deux fluides est décrite par une méthode level set, sur laquelle est prise en compte la force capillaire

Investigation of indentation-, impact- and scratch-induced mechanically affected zones in a copper single crystal

International audienceMany nanomechanical testings and surface mechanical treatments—burnishing, shot peening...—are based upon contact phenomena such as indentation, impact and scratch loadings. In this paper, the Mechanically Affected Zone (MAZ) induced by these standard contact loadings applied on a single crystal copper is investigated. We assume that the MAZ can be characterized by the lattice misorientation measured using backscattering electron diffraction. With the help of a Finite-Element analysis, it is shown that crystal plasticity theory can estimate with enough accuracy the lattice misorientation pattern. Experimental results highlight that the MAZ size is always related to the residual imprint dimension and its shape depends strongly on the kind of loading

Simulation numérique du procédé par infusion de résine d’une nouvelle génération de renforts structuraux pour l’aéronautique

Cet article présente une approche numérique pour la simulation de l’élaboration par des procédés par infusion de résine de pièces composites hautes performances de grandes dimensions. Ce modèle s’appuie sur une approche monolithique pour la résolution d’un couplage Stokes-Darcy, modélisant l’écoulement dans un milieu non poreux (Stokes) et dans des préformes fibreuses assimilées à des milieux poreux orthotropes (Darcy). Les grandes déformations subies par les préformes fibreuses pendant le procédé sont prises en compte au moyen d’une formulation lagrangienne réactualisée. L’interaction fluide-structure est modélisée au travers de relations contrainte-déformation identifiées expérimentalement permettant de rendre compte de l’influence de la déformation de la préforme sur la perméabilité du milieu poreux et donc sur l’écoulement fluide. La rétroaction de la résine sur les préformes est décrite par la loi de Terzaghi introduisant, au cours du procédé, un phénomène de gonflement des préformes via la pression de la résine