Predicting sizing dependent bending rigidity of glass fibre bundles in sheet moulding compounds

The effect of sizing on bending rigidity in fibre bundles was investigated. Particular attention was paid to the effect of film formers and anti-static agents on the behaviour of glass fibre bundles under forced packing conditions. The bending rigidity of different types of bundle was estimated through the nail test, the Kawabata test, and packing stress experiments coupled with micromechanical analysis. An analytical expression describing the packing stress versus fibre volume fraction was derived for bundles with elliptical cross-section. The predicted values for bending stiffness of bundles were in good agreement with direct experimental measurements. These showed that sizing formulation may affect bundle rigidity and the compressive behaviour of dry fibre suspensions.

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Emmanuelle Comte, Jan-Anders Månson, Véronique Michaud
2006
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https://infoscience.epfl.ch/record/89698?ln=en

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Correlation between sizing formulation and compressive behaviour of concentrated glass bundle suspensions

Emmanuelle Comte, Jan-Anders Månson, Véronique Michaud

The correlation between sizing formulation, bundle mechanical characteristics, and bundle-matrix static and dynamic interactions are investigated. Two glass-fiber sizing formulations are considered, one containing polyvinyl acetate (PVAc) and the other polyester/PVAc, as conventionally used in sheet molding compounds (SMC). Axial compression tests are conducted on dry two-dimensional (2D) random suspensions. The forced packing is governed by the bending of fiber bundle segments between bundle-bundle contact points. Benchmarking of the experimental curves with a modified theoretical model provides an estimation of the fiber bundle bending rigidity under forced packing conditions. This value is found to depend on the bundle sizing as well as on the interaction with solvents present in the matrix as is the case for SMC. Free flow and molding experiments are performed on planar SMC sheets using the two different fiber bundles as reinforcements. The results confirm the dependence of the molding energy and the SMC rheology on the bundles chemical and mechanical characteristics.

2005

Void Formation And Transport During SMC Manufacturing: Effect Of The Glass Fibre Sizing

Emmanuelle Comte, Jan-Anders Månson, Véronique Michaud

The present study investigates the origin of voids in sheet molding compounds (SMCs) sheets and their transport during the manufacturing steps. Paste mixing, impregnation, thickening, and molding have been performed with five different SMC sheets, one without fibers and the others with four different types of glass fiber bundles. The fiber surface energy and bending rigidity were quantified, together with the paste surface energy. Void content was then measured at each manufacturing step. Two main void origins in SMC sheets have been observed: (i) air entrapment during paste mixing and (ii) poor bundle impregnation. These voids may be largely removed during SMC manufacturing. The quality of impregnation and void elimination during the flow is found to depend on the bundle characteristics (rigidity and surface energy) conferred by their sizing and over sizing.

2006

Glass fiber

Glass fiber (or glass fibre) is a material consisting of numerous extremely fine fibers of glass. Glassmakers throughout history have experimented with glass fibers, but mass manufacture of glass fi

Compressive strength

In mechanics, compressive strength (or compression strength) is the capacity of a material or structure to withstand loads tending to reduce size (as opposed to tensile strength which withstands loa

Sizing

Sizing or size is a substance that is applied to, or incorporated into, other materials—especially papers and textiles—to act as a protective filler or glaze. Sizing is used in papermaking and textile