Showing papers on "Fiber published in 1980"

Determinants of conduction velocity in myelinated nerve fibers.

Abstract: This article reviews the determinants of conduction velocity in myelinated nerve fibers. For fibers exhibiting geometric similarity, conduction velocity is nearly proportional to diameter. However, in classes of geometrically similar fibers, myelin thickness and internode distance are linearly related to diameter. Therefore, it is not possible to assess the relative contributions of each of these factors. The relative effects of changes in each of these parameters on conduction velocity can be assessed from studies on fibers representing different similarity classes or from theoretical parametric studies. These studies show that for a fixed axon diameter, conduction velocity increases with myelin thickness. For a fixed total fiber diameter, there is an optimal ratio of axon diameter to total fiber diameter (and therefore to myelin thickness) at which conduction velocity is maximized. Conduction velocity is dependent on internode distance, with a broad maximum centered around the value observed in normal peripheral fibers. Conduction velocity is also dependent on temperature and the properties of the axonal milieu. Thus, the conduction speed of any given fiber reflects a number of parameters and is not determined by any single structural characteristic.

Shear flow rheological properties, fiber damage, and mastication characteristics of aramid-, glass-, and cellulose-fiber-reinforced polystyrene melts

Abstract: An experimental study of the viscosity and principal normal stress difference of a polystyrene melt filled with aramid (Kevlar), glass, and cellulose fibers is reported. The influence of loading level and mastication on the rheological properties is discussed. The effects of mixing and mastication on fiber damage are considered. Glass fibers break down rapidly to very small aspect ratios, while aramid shows a “kinked” structure, with kinks occurring every 100 μm. A mechanism is proposed for fiber breakage based on buckling during rotation in shear flow. It is found that addition of fibers increases the viscosity in the same manner as a reduction in temperature, and data may be superposed by reduced plotting. This indicates that the viscosity increase is due solely to enhanced viscous dissipation in the matrix and not to interparticle forces as is the case with smaller particles. The principal normal stress difference increases at fixed shear stress with fiber loading. The extent of increase depends upon fiber loading, aspect ratio, and modulus.

A Novel Approach to Gas Separations Using Composite Hollow Fiber Membranes

Abstract: A method has been developed by which a porous hollow fiber which cannot separate gases to a significant extent can be made to exhibit its intrinsic separation properties by coating with an appropriate material. A unique feature of this composited fiber is that the separation properties are determined by the porous support polymer rather than by the coating polymer. The hollow fibers produced by this method have extraordinarily high rates compared to earlier hollow fibers used for gas separations. In addition, they can function under extremely high pressure gradients. Gases such as He, H2, and CO2 can be separated from gases like CH4, CO, and N2, and the system is chemically and physically stable to a wide range of typical industrial contaminants. As a result, systems based on these fibers should be useful in a variety of processes, some of which include stream splitting, gas composition control, H2 upgrading, and purge gas recovery.

Rheology of short glass fiber-reinforced thermoplastics and its application to injection molding I. Fiber motion and viscosity measurement

Abstract: A study has been made of the fiber orientation in short glass fiber-filled thermoplastics resulting from convergent, divergent and shear flows. Convergent flow results in high fiber alignment along the flow direction, whereas diverging flow causes the fibers to align at 90° to the major flow direction. Shear flow produces a decrease in alignment parallel to the flow direction and the effect is pronounced at low flow rates. Non-linear Bagley plots have been observed, under some conditions, during rheological measurements. The data are consistent with a pressure dependent viscosity.

Continuous drawing of liquids to form fibers

Abstract: The continuous stretching of viscous liqu ids to form fibers is a primary manufacturing process in the textile industry. The mechanics of certain sheet formation and sheet and wire coating operations are quite similar, as are the mechanics of the formation of glass fibers. Most published experimental and theoretical work has been motivated by applications using polymeric liquids, where the interactions between processing conditions and the complex fluid rheology are of particular interest. The melt spinning process for the manufacture of textile fibers is shown schematically in Figure 1. Molten polymer is extruded through a small hole into cross-flowing ambient air at a temperature below the solidifica­ tion temperature of the polymer. The solidified polymer is taken up at a higher speed than the mean extrusion velocity, resulting in drawing of the filament. The steady-state ratio of extrusion to takeup area is known as the draw ratio (DR); the draw ratio is also equal to the steady-state ratio of takeup to extrusion velocity (to within the approximation that polymer density is independent of temperature). Typical processing variables for the manufacture of poly (ethylene terephthalate) (PET) fiber are shown in Table 1. Commercial PET, a polyester sold under such trade names as Dacron, Terylene, and Fortrel, is a nearly amorphous material as spun, although PET with forty percent crystalline polymer can be produced. Other commercially important melt-spun polymers include Nylon-6, Nylon-66, and polypropylene. The solidified filament is typically subjected

Static pressure sensitivity amplification in interferometric fiber-optic hydrophones

Abstract: The induced optical phase change produced when a static pressure is applied to the test arm of an interferometric single-mode fiber optic hydrophone is examined in terms of hydrostatic and radial mechanical models. The expressions for the models are given in terms of a 3-D solution to the equations of elastostatics for multilayered cylinders. The induced phase change is calculated using both models for various values of the diameter and elastic properties of fiber jacket materials. It is shown that the phase change predicted from the 3-D approach for each model can be adequately described in terms of much simpler 2-D plane strain models. Calculations show that the hydrophone sensitivity of a jacketed fiber is amplified compared with a bare fiber. The largest increase in sensitivity is predicted with the radial model. Calculated sensitivities for the hydrostatic model are shown to correspond closely in value with static pressure sensitivity measurements for the experimental arrangement used here.

Self-aligning optical fiber connector

Abstract: An optical fiber connector having two half-round holding members (40) mounted in a central coupler (10). The half-round members (40) have flat mating surfaces (42) with an opposed longitudinal V-groove (44) for receiving fiber ends (56) of either similar or dis-similar diameters. The opposed fibers (56) spread the holding members away from each other; an elastic member (52) retains the holding members in opposed relationship.

Melt crystallization of polypropylene: Effect of contact with fiber substrates

Abstract: The isothermal crystallization of isotactic polypropylene at different temperatures in the presence of fibrous substrates has been investigated. It is shown that preferential transcrystalline growth occurs at the fiber surface and that changes in nucleation density in the bulk material adjacent to the fibers also occur, the extent of which is dependent on temperature and fiber volume fraction. The effects are discussed in terms of the diffusion of heterogeneities in the bulk due to interaction and the adsorption on the fibers.

Rheology of short glass fiber-reinforced thermoplastics and its application to injection molding. II. The effect of material parameters

Abstract: The effect of fiber concentration, fiber length, and temperature on the shear viscosity and die swell of several short glass fiber-filled thermoplastics has been determined. In addition, a study of the injection molding behavior of these materials has been performed. At low shear rates, viscosity increases appreciably with both fiber length and fiber concentration, but at high shear rates the effect is much less pronounced. A qualitative explanation is proposed for these effects in terms of the fiber orientation studies reported in Part I of this paper (1). The die swell is an important parameter in determining the method of mold filling of these materials, and depends strongly on fiber length.

Experimental Studies of the Influence of Particle and Fiber Reinforcement on the Rheological Properties of Polymer Melts

Abstract: An experimental study is reported on the rheological properties of compounds of a polystyrene melt with calcium carbonate, carbon black, titanium dioxide, calcium sulfate anhydride fiber, mica, glass beads and aramid, cellulose and glass fibers. Comparison is made of the shear viscosity, elongational viscosity and principal normal stress difference of these compounds at 20 volume per cent loadings. The polymer matrix and compounds with the smallest particle dimension greater than 10µ exhibit low shear rate Newtonian viscosities. Suspensions with particle sizes 0.5µ and smaller exhibit yield values. Yield values are also observed in elongational flow for systems exhibiting yielding in shear flow. The experimental data are contrasted to both mechanistic theories of suspensions with interaction between particles and a phenomenological plastic-viscoelastic tensor constitutive equation.

Composite materials made from plant fibers bonded with portland cement and method of producing same

Abstract: The specification discloses a method of producing composite building materials from a mixture of plant fibers bonded with portland cement. Plant fibers, cement and soluble silicates in certain proportions are mixed and heated under pressure for a short period to get physically stable product that can be cured under atmospheric conditions to full strength. The plant fibers may initially be pretreated with an aqueous solution containing dichromate or permanganate ion prior to adding the cement to negate the adverse effects of set inhibiting water-soluble compounds in the fiber. Other chemicals may be added to modify the reaction and improve the product.

Optical fiber launch coupler

Abstract: A low-loss unidirectional optical coupler utilizing clad monofilament fibers of different diameters is provided by mounting each fiber on a curved surface, lapping the smaller (launch) fiber substantially tangentially to the curved surface until the core of the launch fiber has been lapped through to produce two elliptical flat surfaces, independently lapping the other (throughput) fiber tangentially to its surface to produce a fiber surface of substantially the same size as one of those produced on the launch fiber, aligning the throughput fiber surface with one of the launch fiber surfaces, and bonding them together.

Fiber Raman lasers

Abstract: Optical fibers can exhibit wavelength conversion and other nonlinear optical effects at powers less than one watt. The reason has little to do with the glass in the fiber core, which is one of the least nonlinear of all materials, but rather with the tremendous interaction length possible in low-loss fibers. The combination of low power and well-controlled geometry makes fibers a particularly useful medium for the study of nonlinear optics. There will also be device implications any time nonlinear effects can be produced at low powers. Of course, the presence of such effects has implications for fiber communications since fiber transmission lines may not always be completely passive devices.

Fabric structure for fiber reinforced plastics

Abstract: Disclosed is a fabric structure for fiber reinforced plastics, which comprises at least two yarn groups composed of straight reinforcing filamentary yarns composed of carbon fibers being free of bends and gathered in one direction in the form resembling a sheet, wherein the yarn groups are integrated with each other by auxiliary filamentary yarns so that the sheet-like faces of the yarn groups are made to confront each other and reinforcing filamentary yarns of one yarn group intersect reinforcing filamentary yarns of the other yarn group, and the auxiliary filamentary yarns have a higher elongation at break than that of the reinforcing filamentary yarns.

Internal combustion engine and composite parts formed from silicon carbide fiber-reinforced ceramic or glass matrices

Abstract: A high strength, fracture tough, high temperature oxidatively stable, heat insulating internal combustion engine combustion chamber component is described made of a silicon carbide fiber reinforced ceramic matrix or a silicon carbide fiber reinforced glass matrix material. An internal combustion engine containing combustion chamber components as above described is also disclosed.

Continuous length silicon carbide fiber reinforced ceramic composites

Abstract: A silicon carbide fiber reinforced ceramic matrix composite is disclosed having high strength, fracture toughness, and oxidative stability even at high temperature use. The composite is made up of a plurality of ceramic layers, each layer reinforced with a plurality of unidirectional continuous length silicon carbide fibers, each layer having an axial flexural strength greater than 70,000 psi and a high fracture toughness, exemplified by a critical stress intensity factor greater than 10×103 psi (inch)1/2. The composite is formed by starting with the ceramic matrix material in the glassy state and converting it from the glassy state to the ceramic state after densification of the composite.

Nouvelle méthode de mesure de la réponse impulsionnelle des fibres optiques.

Abstract: A new technique for measuring the temporal transfer function of optical fibers is described. The method consists of placing the fiber under test in one arm of a Mach-Zehnder interferometer excited by a broadband source. The temporal impulse response is obtained from a holographic reconstruction. The method requires only short lengths of single-mode or multimode fibers (less than 1 m). We have measured a dispersion of 0.3 nsec/km.nm at 0.59 microm with a single-mode fiber, in good agreement with theory. The arrival times of the various modes of multimode fibers are resolved.

Methods for preparing tube sheets for permeators having hollow fiber membranes

Abstract: A high degree of openness to the bores of hollow fiber membranes in a tube sheet can be achieved by impacting the region of the tube sheet at which hollow fiber membranes terminate with a particulate abrasive having an average maximum dimension of less than about 70 percent of the minimum dimension of the bores of the hollow fiber membranes. The particulate abrasive is impacted on the tube sheet at a velocity sufficient to erode the surface of the hollow fiber membranes.

Adhesion efficiency between phases in fibre-reinforced polymers by means of the concept of boundary interphase

Abstract: The role of the boundary interphase on the adhesion efficiency between fiber and matrix in the case of polymers reinforced with unidirectional fibers was investigated. A theoretical model was introduced considering that the composite material consists of three phases; that is, the fiber, the matrix and the interphase, material which is the part of the polymer matrix lying at the close vicinity of the fiber surface. The interphase material, having different physical properties from those of the bulk matrix, affects the overall behavior of the composite. Moreover, the quality of adhesion between the two main phases depends greatly on the nature of the interphase material. In this study we have considered that the interphase material is inhomogeneous in nature, with properties varying continuously from the fiber surface to the bulk matrix. The theory developed resulted in a criterion of the adhesion quality and in a prediction of the longitudinal modulus of elasticity of the fiber-composite.

Optical fiber beam splitter couplers employing coatings with dichroic properties

Abstract: A single fiber of any glass type is cut at a suitable angle and both halves are then polished at the end surfaces. A layer of material having dichroic properties or multiple layers are then deposited on one coupler half and the two halves are rejoinded with the angular faces in alignment. Each of the cut fibers are supported in a potting compound. A third fiber is added relatively transverse to the original fibers in order to receive light from the deposited layer. This fiber is associated with one port, while the other fibers are associated with two other ports, thus providing a three port coupler device.

Ultra-high strength polyethylene by hot drawing of surface growth fibers

Abstract: Hot drawing at 150°C has been applied to high molecular weight polyethylene fibers produced by flow induced crystallization in a Couette apparatus, referred to as the ‘surface growth’ technique. A distinct improvement of the tensile properties of the fibers was noticed upon drawing. A tensile strength at break of 4.7 GPa was reached. Drawability is discussed in relation to fiber morphology. The shish-kebab like structure of the ‘surface growth’ fiber was transformed into a morphology consisting of smooth fibrils upon drawing.

Method for the production of a fiber-reinforced hydraulically setting material

Abstract: Asbestos-free fiber reinforced hydraulically setting materials, which comprise a slurry of one or more hydraulic binding agents, fibers, water and perhaps additional additives, are obtained when, as fiber, 2 to 20% by volume of filter fibers and 0,5 to 20, preferably 1 to 10% by volume reinforcing fibers are used, both of which are subjected to preliminary treatment which improves their dispersability. By means of the preliminary treatment the fibers can be uniformly distributed in the slurry. The material can be worked on apparatus common for the production of asbestos cement and used for the same purposes as asbestos cement.

Rheology of molten blends of polyoxymethylene and ethylene‐vinyl acetate copolymer and the microstructure of extrudates as a function of their melt viscosities

Abstract: Blends of polyoxymethylene (POM) with a copolymer of ethylene and vinyl acetate (CEVAc) have been studied. The effect of viscosity ratio for melts of the components on the processes of fiber formation in extrudates and on the rheological properties of the molten blend has been tested. The viscosity ratio of the fiber-forming POM and the matrix varied in the range 0.35-27.7. POM ultrathin fibers of unlimited length can be formed in the CEVAc only at a viscosity ratio close to unity. For ratios much greater than unity, the extrudate is found to contain short fibers and a finely dispersed powder or no fibers at all. If the viscosity of the POM melt is lower than that of the matrix, films are formed in addition to fibers. The second factor that governs fiber formation is the extrusion shear stress. An optimum shear stress exists at which the amount of ultrathin fibers is a maximum.

Silicon carbide fiber reinforced glass composites

Abstract: Silicon carbide fiber reinforced glass composites are disclosed having high strength, fracture toughness, and oxidative stability, even in high temperature use environments. Disclosed composites include silicon carbide fiber reinforced borosilicate glass, high silica content glass, and aluminosilicate glass. Flexural strengths in excess of 40,000 psi up to temperatures as high as 1150° C. are attained with such composites.