Degree Of Fiber Dispersion Research Articles

Rheological and Mechanical Properties of Kenaf and Jute Fiber-Reinforced Cement Composites

This study investigated the rheological and mechanical properties of cement composites with kenaf and jute fibers for use in shotcrete. The length and volume fractions of the fiber were varied; the rheological properties were analyzed in terms of air content, compression and flexural tests were conducted, and the degree of fiber dispersion was assessed using fluorescence microscopy. The rougher surfaces of the jute fibers led to a higher yield stress and viscosity of the composite compared to the kenaf fibers. The use of 10-mm-long jute fibers at 2.0% volume fraction led to optimal rheological properties while 30-mm-long jute fibers at 1.0% resulted in the worst properties. The yield stress and plastic viscosity exhibited positive and negative correlations with the fiber volume fraction, respectively. This was likely because of the bridging and fluid actions of the bubbles at higher fiber content. For a given fiber content, only the yield stress increases with an increase in fiber length. Although all the mechanical properties deteriorated (compressive strength decreased from 27.5 to 6 MPa, and flexural strength deteriorated from 6.2 to 1.8 MPa), the mixtures failed in a ductile manner. Using 10-mm-long kenaf fibers at 2.0% induced optimal fiber dispersion, whereas the minimum dispersion-coefficient value was found for 5-mm-long kenaf fibers at 0.5%.

Enhancing the flexural performance of ultra-high-performance concrete using long steel fibers

In this study, the flexural performance and fiber distribution characteristics of ultra-high-performance concrete (UHPC) were investigated according to the fiber length. To do this, three different fiber lengths having an identical diameter were used. Enhancements in flexural strength and energy absorption capacity were observed when longer fibers (or higher aspect ratios of fiber) were used, whereas insignificant effect of fiber length on the first cracking properties (i.e., first cracking strength and corresponding deflection) was obtained. Fiber length had a little influence on the degree of fiber dispersion, but a significant influence on the fiber orientation. A higher fiber orientation coefficient along the flow distance was obtained when shorter fibers were used. A finite element analysis incorporating previously suggested material models was performed and verified by comparing the analytical results with the present experimental data.

On the modeling of fiber dispersion in fiber-reinforced elastic materials

When an isotropic material is subject to a uniaxial tension, the principal strain transverse to the direction of applied load is always negative. However, in fiber reinforced materials the transverse principal strain can change its sign as the load increases, passing through the zero-points, known as perversions. We investigate how the number of perversions in a material reinforced by two symmetrically aligned families of distributed fibers depends both on the degree of fiber dispersion and the model used for fiber dispersion. Angular integration and three variants of the generalized structure tensor approach are considered and discussed. The study of perversions clearly demonstrates the qualitative difference between these approaches in the case of high dispersion of fibers. The results suggest that this difference is primarily due to the way compressive fibers are modeled.

Recycled carbon fibre reinforced polymer composite for electromagnetic interference shielding

This paper describes the development of an electromagnetic interference shielding material using recycled carbon fibre. Fibre recycled from a fluidised bed process was transformed into a non-woven veil and was moulded into a glass-fibre reinforced polymer plaque to provide shielding. Factors affecting shielding performance were established using a virgin fibre and the result was compared with veil made of the recycled fibre. Shielding performance increased with veil areal densities. The influence of fibre length on shielding seemed insignificant provided the fibre was distributed evenly. Sandwiching the plaque between fibre veils enhanced the shielding performance. A shielding value of 40 dB was attained from a layer of 80 g/m 2 recycled fibre veil and it was increased to 70 dB when the plaque was sandwiched between two layers of 30 g/m 2 recycled fibre veil. The correlation between veil formation and shielding effectiveness was established and found that shielding effectiveness increased with the degree of fibre dispersion.

Vapor grown carbon fiber composites with epoxy and poly(phenylene sulfide) matrices

Abstract Vapor grown carbon fibers (VGCF, Pyrograf III™ from Applied Sciences, Inc.), with 100–300 nm diameters and ∽10–100 μm lengths, were formulated in various fiber volume fractions into epoxy (thermoset) and into poly(phenylene sulfide) (thermoplastic) composites. Increases in stiffness were observed as with previous VGCF/organic matrix composites. Large increases in flexural strengths were achieved in both systems demonstrating for the first time that discontinuous randomly oriented Pyrograf III™ can give strength increases and has substantial potential as a reinforcement in composites. Here-to-fore, addition of VGCF caused strength decreases. Voids, residual thermal strains (as the fiber surface area is ∽35 times greater than 7 μm-diameter PAN fiber), or uncertainties about fiber strength, fiber–matrix bonding and the degree of fiber dispersion, could cause losses of strength. Thermal conductivity properties of VGCF/ABS (acrylonitrile–butadiene–styrene from GE Plastics) and VGCF/epoxy composites with various fiber volume fractions were measured. Thermal conductivity increased with an increase in fiber volume fraction. However, these increases were not significant enough to make these VGCF fiber/organic matrix composites candidates for thermally conductive materials.

Studies of the flexural properties of asbestos-reinforced phenolic composites

Factors which may influence the flexural strength of asbestos-reinforced phenolic composites were investigated. These are: fibre-to-resin adhesion, the degree of fibre dispersion, the relative fracture strains of the fibres and matrices, and voids. Fibre-to-resin adhesion was promoted by pre-coating asbestos fibres with phenol-formaldehyde in solution state throughin situ polymerization. Fibre dispersion was controlled by applying shear agitation to the mixture of fibres in solution duringin situ polymerization. The ratio of the fracture strain of the fibres to that of the matrix was varied by using resins having different fracture strains. Voids were found to be present in all cases. The size of voids was not significantly affected by different processing conditions.