Function Of Fiber Content Research Articles

419 マニラ麻繊維強化クロスプライ・グリーンコンポジットの強度特性評価

This paper discusses mechanical properties of cross-ply "Green" composite material made from woven Manila hemp fibers and biodegradable polymer. The mechanical properties of the composites have been evaluated as a function of fiber content. The tensile strength increased with the fiber content until 50mass% and leveled off thereafter. This dependence on the fiber content is due to the decrease in fiber strength caused by fiber damages introduced during hot-pressing. In order to decrease the damage of fibers aligned in loading direction, the fiber sheet was produced by using hemp fibers for weft and cotton fibers for warp. As a result, the tensile strength of cross-ply composites increased from 153MPa to 171MPa.

Matriz termofixa fenólica em compósitos reforçados com fibras de bagaço de cana-de-açúcar

Neste trabalho, a lignina extraída pelo processo organossolve do bagaço de cana-de-açúcar substituiu parcialmente fenol (40% em massa) em matrizes termofixas reforçadas com fibras curtas de bagaço de cana-de-açúcar (30, 40, 50, 60 e 70%, v/v). Os compósitos obtidos foram caracterizados por TG, DSC, DMTA, Resistência ao Impacto Charpy, Dureza Shore D. Os resultados obtidos mostraram ser viável a substituição de fenol por lignina em matrizes fenólicas. No entanto, para que se obtenha compósitos com propriedades compatíveis com às exigidas para aplicações industriais, modificações devem ser feitas: modificação de fibras por meio de reações químicas, diversificação do comprimento das fibras vegetais, realização de etapas de cura em temperaturas superiores as consideradas no presente trabalho.

Fatigue crack propagation in polypropylene reinforced with short glass fibres

Fatigue crack propagation (FCP) behaviour of polypropylene composites reinforced with short glass fibres has been investigated as a function of fibre content and frequency of the sinusoidal applied load. The FCP resistance of the composites was found to improve as the fibre weight fraction increased. Results for all composites showed a dramatic decrease in the crack growth rate per cycle as a result of increasing frequency, at any given crack length. A further analysis of the data indicated that crack propagation was governed by viscoelastic creep which produced, at the lower frequencies, a crack speed approximately independent of frequency. However, it was recognized that at the highest frequency hysteretic heating at the crack tip induced a higher crack speed, associated with non-isothermal creep processes.

Strength and Deformation Properties of Soils Reinforced With Fibrillated Fibers

The results of preliminary laboratory tests on a clay and a sand reinforced with randomly distributed fibrillated fibers are presented. The results of compaction, direct shear, unconfined compression and California Bearing Ratio (CBR) tests are described. The influence of test parameters such as normal stress, the amount of reinforcement, specimen size, and moisture content is addressed. The tests show that fibers significantly increase the peak compressive strength of clay and sand. The addition of fiber reinforcement in the sand and clay specimens resulted in substantial increases in the peak friction angle and cohesion values. The increase in strength is a function of fiber content and moisture content. The Mohr-Coulomb failure envelopes for the clay specimens are described by a combination of curvilinear and linear sections. The CBR values for the clay and sand specimens were also significantly improved using fiber reinforcement. This preliminary study suggests that for the soils tested and reinforced with 25 mm long polypropylene fibrillated fibers, the optimum fiber content is approximately 0.3% of the dry unit weight of the soil.

The Internal Damping of Al-Al2O3 (f) Composites During Thermal Cycling : the Effect of Fibre Content and Matrix Strength

A simple model is proposed to describe the observed effect of the volume fraction of fibres on the internal friction, elastic modulus and deformation at zero applied stress during the cooling portion of a thermal cycle between 450 K and 100 K. The sample is considered as composed by three phases, each one showing different intrinsic damping: the reinforcing fibre, the aluminium matrix far from the fibre and the zone around the fibre, close to the matrix-fibre interface, called the plastic zone. It is assumed that the main contribution to the internal friction arises in these plastic zones, which grow during cooling in a non strain hardening matrix. A uniform dislocation density in the zone is considered. The internal damping of the whole sample is predicted, as a function of fibre content, for the limit case of uniform strain. The model predicts satisfactorily the characteristic temperatures defined in the elastic modulus curve if they are identified as the temperatures for the beginning of growth of the plastic zone, and the temperature for overlapping of fully developed zones, respectively.

Dynamic properties of short fiber–EPDM matrix composites as a function of strain amplitude

AbstractThe dynamic properties of composite materials consisting of an ethylene–propylene rubber matrix (EPDM) and short polyester polyethylene‐terephthalate (PET) fiber vary with dynamic stress amplitude applied to the material. These variations support the statement that fiber treatment with 1,4‐carboxy‐sulphonyl‐diazide, which acts as a bridge between the fiber and the matrix and hence enhances the strength of the interface enabling it to resist greater strain applied to the composite and, as a consequence, yielding greater retention values of the storage modulus, measured longitudinally to preferential fiber orientation, E′L. By means of transversal measurements of the storage modulus, E′T, of these materials it is possible to determine a parameter b, which eventually indicates the degree of matrix–fiber bonding and which is consistently higher for materials filled with surface‐treated fiber. This enhanced phase adhesion is further confirmed by higher equivalent interfacial thickness values, ΔR, which, in addition, vary less with increasing dynamic strain amplitude. Finally dissipated energy variation or mechanical energy loss, Eloss, is studied as a function of fiber content and strain amplitude. Experimental findings show Eloss to increase with fiber content and strain amplitude, when measured at constant strain amplitude ϵ0, and to yield higher values for treated fiber samples. © 1994 John Wiley & Sons, Inc.

Deformation and fracture of glass-mat-reinforced polypropylene

The mechanical properties of glass-mat-reinforced thermoplastics, GMT, can be varied within wide limits through the choice of glass mat, fibre content, and thermoplastic matrix. A great variety of fibre configurations and fibre contents is commercially available. In order to understand how the fibre structure of GMT materials controls the mechanical properties, two structurally different GMT materials were studied. Several grades with different fibre contents were used for each material. One material had short fibres (12 mm long), discretely dispersed with in-plane random orientation. The other material had in-plane continuous looped bundles of fibres. The deformation and fracture of these materials have been studied as a function of fibre content. The present work shows that the material with discretely dispersed fibres has higher values of tensile creep modulus, tensile strength, elongation at fracture, and work of fracture (area under the stress/strain curve). The results are discussed and related to the structural differences between the two materials.

Polyethylene-Ultra High Modulus Polyethylene Short Fibers Composites

Composites based on chopped ultra high modulus polyethylene fibers (UHMPE) and low density polyethylene (LDPE) were prepared in the melt state. It is shown that the UHMPE fibers do not melt during the preparation operations, and an im portant enhancement of the mechanical properties is obtained as a function of fiber content and length. The efficiency of these fibers was found to be comparable to those of Kevlar® fibers, and higher than those of glass fibers. An important transcrystalline region has been observed for all the fibers, however, its effect on their efficiency as a reinforcing agent is questionable. It is also shown that UHMPE fibers can advantageously replace Kevlar® fibers in some particular applications.

Weldline strength in injection molded glass fiber‐reinforced polypropylene

AbstractWeldlines are inescapable byproducts of the injection molding process. They represent potentially fatal flaws particularly in multiphase materials. In this work weldlines in injection molded glass fiber‐reinforced polypropylene (0 to 40wt%) were studied as a function of the cavity shapes and depths. It was found that the weldline is a zone between 2 and 8 mm wide extending throughout the thickness in which the fibers are oriented almost perfectly in a plane parallel to the weldline. While the strength of moldings without weldlines depends on the mold shape and on the fiber concentration, the weldline strength is a function of fiber content only. A simple model based on the assumption of complete debonding of the fiber‐matrix interface when failure occurs can be used to predict the strength loss in the weldline.

Electrical resistivity of copper reinforced with short carbon fibres

The electrical resistivity of copper reinforced with short aligned carbon fibres has been measured in axial and transverse directions as a function of fibre content. The results have been considered in the light of predictions from the Eshelby equivalent homogeneous inclusion method for modelling of conduction. Higher resistivities, particularly for transverse current flow, were observed than is predicted on the basis of an isotropic matrix resistivity equal to that of unreinforced copper. This is thought to be explicable in terms of the effect of relatively high levels of elongated porosity present in the specimens examined.

Carbon fibre reinforced glass matrix composite tension and flexure properties

Carbon fibre reinforced borosilicate glass matrix composites have been fabricated to determine their mechanical properties in tension and flexure. Composite tensile stress-strain properties, including elastic modulus, proportional limit and ultimate tensile strength, have been measured as a function of fibre content. Composite tensile properties were also obtained at temperatures of up to 625° C through the testing of 0/90 cross-plied specimens. Composite short-beam shear strength was found to depend on specimen orientation and also on the composition of the glass matrix. This compositional dependence was associated with an independent measurement of the fibre-matrix interfacial shear strength and was related to the degree of fibre-matrix reaction taking place during composite fabrication.

Anisotropic electrical conductivity in heterogeneous solids with cylindrical conducting inclusions.

The electrical conductivity of undirectional short-graphite-fiber reinforced polymers is studied as a function of fiber content. An insulator-to-conductor transition is evidenced. In its neighborhood the electrical conductivity is anisotropic, the direction of highest conductivity being parallel to the fiber axis of alignment. It is found that the anisotropic ratio is finite at threshold and is related to the fiber aspect ratio. Its decay and the critical behaviors of the parallel and perpendicular conductivities as the fiber content is increased are interpreted in the framework of anisotropic percolation theory.