Assessment of capillary phenomena in liquid composite molding

The interplay between capillary and viscous forces plays a significant role for optimal part quality in fiber-reinforced composites manufactured by Liquid Composite Molding (LCM); these are however difficult to analyze during flow. Two approaches are proposed in this study: (i) a woven glass fabric’s surface was modified by corona treatment to improve its wetting characteristics without altering its permeability, (ii) flow of a UV-curable resin was stopped during LCM by fast radiation cure. Capillary rise experiments and unsaturated/saturated permeability measurements confirmed the wetting improvement by corona treatment. Flow front morphology analysis of cured pristine and treated fabrics, processed under various pressure differentials, revealed the enhancement of dual-scale flow at capillary-dominated regime and improvement of intra-tow flow in viscous-dominated regime. Furthermore, the obtained results provide insight into the so-called optimal capillary number to attain the minimal void content in composites and its alteration by surface treatment of fiber reinforcements.

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Baris Çaglar, Feyza Karasu Kiliç, Véronique Michaud, Cem Tekin
2019
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https://infoscience.epfl.ch/record/264837?ln=fr

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Matériau composite

vignette|Multicouche, un exemple de matériau composite. Un matériau composite est un assemblage ou un mélange hétérogène d'au moins deux composants, non miscibles mais ayant une forte capacité d'inter

Surface

A surface, as the term is most generally used, is the outermost or uppermost layer of a physical object or space. It is the portion or region of the object that can first be perceived by an observe

Capillarité

La capillarité est le phénomène d'interaction qui se produit aux interfaces entre deux liquides non miscibles, entre un liquide et l'air ou entre un liquide et une surface. Elle est due aux forces de

Phase separation at the fiber-matrix interface in composites based on a thermoplastic/polyester blend

Xavier Bulliard, Jan-Anders Månson, Véronique Michaud

A study of the microstructure developing at the surface of glass fibers in a poly(vinyl acetate) (PVAc)/polyester blend is presented. Three different experimental methods are used: a technique based on the Wilhelmy method to measure the wettability of the fibers before curing, and both optical microscopy and atomic force microscopy in the pulsed-force mode to characterize potential phases splitting at the fibermatrix interface after curing. It was found that, depending on the curing conditions and the concentration in PVAc, the surface treatment of the fiber could have a significant influence on the microstructure. For a concentration in PVAc lower than 5 wt% and a curing temperature of 80°C, extreme cases, such as the development of layers of one of the phases at the surface or the formation of lenses of one phase, were observed. In other cases, in particular for elevated temperatures and higher concentrations in PVAc, the fibers did not exert a significant influence on the morphology. It was also found that in such a reactive system, surface tension considerations alone are insufficient to explain the configuration of the phases at the surface of the fibers.

2005

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Effect of annealing and silylation on the strength of melt-spun Ni-Mn-Ga fibres and their adhesion to epoxy

Susanne Glock, Yves Leterrier, Véronique Michaud, Edgars Sparnins

Single crystals of ferromagnetic Ni-Mn-Ga shape memory alloys show magnetic-field and stress induced twinning, leading to shape memory. Adaptive composites can thus be produced by embedding single crystalline particles or bamboo-structured Ni-Mn-Ga fibres into a polymer matrix. To guarantee a durable performance of these composites, adhesion between reinforcement phase and matrix should be quantified and optimised. The influence of annealing and surface treatment with an aminosilane of melt-spun Ni-Mn-Ga fibres on their strength and adhesion to an epoxy matrix was investigated using single fibre tension and fragmentation tests. Annealing of the melt-spun Ni-Mn-Ga fibres changed the surface from a "pimpled" to a smooth microstructure. This resulted in a reduced adhesion of the annealed fibres in comparison to the as-spun fibres embedded in an epoxy matrix. As-spun fibres exhibited an interfacial shear strength (IFSS) comparable to the shear strength of the epoxy matrix so that the silylation did not change the adhesion significantly. For the annealed fibres, the silane treatment improved the IFSS by 67%. Furthermore, the silylation increased the fracture strength of the Ni-Mn-Ga fibres due to surface flaw healing or forming of a protective surface coating. (C) 2014 Elsevier Ltd. All rights reserved.

2014

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Capillarity in pressure infiltration: influence of percolation and wetting angle

William Craig Carter, Alain Léger, Andreas Mortensen, Gionata Schneider, Ludger Weber

Composite materials are often produced by pressure-infiltration of a liquid matrix into a preform of packed solid fibers or particles. Capillary forces that intervene in this process are quantified by measuring saturation curves, which are plots of the fraction pore space filled with the matrix versus the pressure difference between the matrix and the atmosphere initially present in the porous preform to be infiltrated. We have constructed an apparatus capable of measuring saturation curves at high temperature (≈1000°C) and high pressures (≈100 atmospheres), which is suitable for the study of metal matrix composite pressure infiltration. Using this apparatus, we study the metal flow path during infiltration, exploring both early and later stages of the process. We measure the effect of capillary parameters derived from sessile drop experiments and known to govern the wetting of ceramics by molten metals, placing focus on copper and its alloys infiltrating preforms of alumina or carbon. We show that initial phases of the process display universal scaling and fractal geometric features that are characteristic signatures of percolation-dominated wetting; later stages of the process obey the Brooks and Corey correlation. We explore the influence of the contact angle and work of immersion by measuring pressure/saturation curves for the infiltration of packed alumina particle preforms by liquid Cu-Al, Cu-Sn and Sn-Al alloys and seek explanations for the observed dependence by means of a network model constructed to combine simplicity with a realistic description of governing microscopic capillary phenomena.

2015

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