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

Effects of hospital facilities on patient outcomes after cancer surgery: an international, prospective, observational study

Background Early death after cancer surgery is higher in low-income and middle-income countries (LMICs) compared with in high-income countries, yet the impact of facility characteristics on early postoperative outcomes is unknown. The aim of this study was to examine the association between hospital infrastructure, resource availability, and processes on early outcomes after cancer surgery worldwide.Methods A multimethods analysis was performed as part of the GlobalSurg 3 study-a multicentre, international, prospective cohort study of patients who had surgery for breast, colorectal, or gastric cancer. The primary outcomes were 30-day mortality and 30-day major complication rates. Potentially beneficial hospital facilities were identified by variable selection to select those associated with 30-day mortality. Adjusted outcomes were determined using generalised estimating equations to account for patient characteristics and country-income group, with population stratification by hospital.Findings Between April 1, 2018, and April 23, 2019, facility-level data were collected for 9685 patients across 238 hospitals in 66 countries (91 hospitals in 20 high-income countries; 57 hospitals in 19 upper-middle-income countries; and 90 hospitals in 27 low-income to lower-middle-income countries). The availability of five hospital facilities was inversely associated with mortality: ultrasound, CT scanner, critical care unit, opioid analgesia, and oncologist. After adjustment for case-mix and country income group, hospitals with three or fewer of these facilities (62 hospitals, 1294 patients) had higher mortality compared with those with four or five (adjusted odds ratio [OR] 3.85 [95% CI 2.58-5.75]; p<0.0001), with excess mortality predominantly explained by a limited capacity to rescue following the development of major complications (63.0% vs 82.7%; OR 0.35 [0.23-0.53]; p<0.0001). Across LMICs, improvements in hospital facilities would prevent one to three deaths for every 100 patients undergoing surgery for cancer.Interpretation Hospitals with higher levels of infrastructure and resources have better outcomes after cancer surgery, independent of country income. Without urgent strengthening of hospital infrastructure and resources, the reductions in cancer-associated mortality associated with improved access will not be realised

Mécanismes d'imprégnation en milieux fibreux : Modélisation et application à la mise en oeuvre des matériaux composites à fibres longues

The aim of this work is to contribute in improving fibrous preforms impregnation for Liquid Composite Molding (LCM) processes. Theoretical and experimental investigations were focused on void that may be appearing during resin injection. Voids or bubbles are mainly formed due to the flow competition inside and outside the yarns. However, the experimental characterization of void formation and transport through the flow inside a fibrous media remains delicate. Since the direct visualization of the liquid flow and the entrapped bubbles in a practical material is uneasy, we use model networks to study the formation of bubbles and their transport. For our experimental studies, a multi-scales approach was adopted considering microfluidic and millifluidic analysis where wetting forces are significant. The obtained results show the influence of those forces on the bubble formation and transport mechanism. A simple model taking into account the interconnectivities between micropore and macropore was suggested. Several geometrical configurations and different flow regimes could be considered by the proposed model. Finally, using this simplified approach it can be possible to compare the forecast results and those obtained in the range of fibrous media impregnation and composites elaboration.L'objectif de ce travail est de contribuer à l'amélioration des mécanismes d'imprégnation d'un renfort fibreux par une résine polymère dans les procédés de mise en œuvre de matériaux composites de type LCM (Liquid Composite Molding). Les études théoriques et expérimentales réalisées se sont focalisées sur les anomalies d'imprégnation pouvant apparaître lors des écoulements. Les défauts couramment observés sont des vides pouvant s'assimiler à des bulles et provenant, en partie, d'une compétition entre les régimes gouvernant les écoulements intra-mèche et inter-mèches. L'analyse de la formation et du transport des bulles au sein d'une structure fibreuse demeure délicate à réaliser du fait de l'architecture complexe de la préforme. Afin de s'exonérer des difficultés rencontrées lors de la visualisation au sein du renfort et pour répondre à cette problématique de vide créé, nous avons fait le choix d'étudier les mécanismes d'imprégnation ainsi que la formation et le transport de bulles dans des réseaux modèles. Une analyse multi-échelles a été adoptée pour nos expérimentations faisant appel à une approche micro et millifluidique où les forces de mouillabilité sont prépondérantes. Les résultats obtenus montrent, dans un premier temps, l'influence de ces forces dans les mécanismes de génération et de transport de bulles et permet de justifier certaines observations proposées dans ce sujet. Un modèle simple basé sur des configurations d'inter-connectivités micropore/macropore a été proposé. Ce modèle permet d'envisager différentes analyses paramétriques selon des configurations géométriques et des régimes d'écoulement variés. Sur cette base, il est possible de prendre en compte différents facteurs et de les comparer à certaines contributions de la littérature dans le domaine de l'imprégnation des milieux fibreux et de la mise en œuvre des composites

Mécanismes d'imprégnation en milieux fibreux (modélisation et application à la mise en oeuvre des matériaux composites à fibres longues)

LE HAVRE-BU Centrale (763512101) / SudocSudocFranceF

Wetting effect on bubble shapes formed in a cylindrical T-junction

International audienc

BUBBLE SHAPE AND TRANSPORT DURING LCM PROCESSES: EXPERIMENTAL MODELING IN A T-JUNCTION TUBE

6 pagesInternational audienceLong fiber composite materials can be elaborated by Liquid Composite Molding (LCM), a family of processes where fibrous preforms are injected by a low viscosity resin. During this process, we have to pay particular attention to the void formation inside the preform because it could modify the material final characteristics. Indeed, a preform presents two different porosity scales: between yarns called macropores and inside yarns, namely micropores

Bubble formation and transport in T-junction for application to Liquid Composite Molding: Wetting effect

International audienc

Characterisation of bubbles formed in a cylindrical T-shaped junction device

International audienc

Modélisation unidimensionnelle multi-physique du comportement d'un joint à faces radiales pour la maintenance d'un circuit carburant

La présente étude porte sur la modélisation unidimensionnelle multi-physique du comportement d'un joint d'étanchéité à faces radiales appelés " garnitures mécaniques " pour des arbres tournants. Ces garnitures fonctionnent à des pressions très élevées générées par le film de lubrification entre les faces des joints dont les performances sont directement affectées par la géométrie de l'interface qui dépend des effets thermiques, mécaniques et de la cinématique appliqués. La modélisation unidimensionnelle proposée prend en compte le transfert thermique et la déformation des faces du joint, couplés au modèle de Reynolds décrivant le champ de pression dans le film lubrifiant. Le choix de ce type de modélisation résulte dans le compromis entre le nombre de paramètres du modèle et la complexité du code de calcul associé. Ce modèle permet ainsi de déterminer de façon simple et rapide les performances caractéristiques d'une garniture mécanique. Cette démarche de modélisation est appliquée au cas d'une garniture mécanique à stator flottant pour un circuit carburant de turboréacteur de faibles dimensions (rayons intérieur et extérieur respectivement de 6 et 7,4 mm) et fonctionnant à des vitesses de rotation relativement faibles (4000 à 5000 tr/min) pour des pressurisations extérieures relativement faibles (0,3 à 0,6 MPa)