Fiber density continuity

This expression is known as the fiber density continuity equation. It states that a fiber, which moves out of one angular position must move into a neighboring one, conserving the total number of fibers. If the initial distribution function, fio, is known, an expression for the angular velocity of the particle, , must be found to solve for eqn. (8.152) and determine how the distribution function varies in time. The motion of the fibers can often be described by the motion of a rigid single rod in a planar flow. 

Barrier Phenomenon. In red cell filtration, the blood first comes into contact with a screen filter. This screen filter, generally a 7—10-) m filter, does not allow micro aggregate debris through. As the blood product passes through the deeper layer of the filter, the barrier phenomenon continues as the fiber density increases. As the path becomes more and more tortuous the cells are more likely to be trapped in the filter. 

In the manufacture of bonded insulating materials, the fibers in the fleece shaft or on the conveyor belt are sprayed with an aqueous binder, generally a phenol-formaldehyde resin. The binder content in the bonded insulating material is 3 to 4%. Compaction to the desired density and hardening of the resin binder occurs in a tunnel kiln, through which the fibers are continuously transported on a conveyor belt. The compaction is achieved with a second belt which exerts the required pressure on the upper surface of the continuous sheet. This is often followed by laminating the sheet with e.g. paper, aluminum or plastic foil. Finally the product is rolled up or cut into sheets. 

A major limitation of the parallel plate technique is limited fiber density and mat thickness, as explained in Sect. 3.2.1. This problem can be overcome by utilizing other forces that are able to overcome the electrostatic repulsive force between nanofibers. Thick aligned nanofiber mats were fabricated across parallel plates when a magnetic field was used to attract fibers to a mesh across parallel plates [97]. Another technique utilized mechanical forces to assemble low density aligned fiber arrays into thicker constructs [98]. This technique used automated tracks to provide continuous mechanical assembly of fiber arrays, and allows theoretically infinite mat thicknesses. 

Visual and Manual Tests. Synthetic fibers are generally mixed with other fibers to achieve a balance of properties. Acryhc staple may be blended with wool, cotton, polyester, rayon, and other synthetic fibers. Therefore, as a preliminary step, the yam or fabric must be separated into its constituent fibers. This immediately estabUshes whether the fiber is a continuous filament or staple product. Staple length, brightness, and breaking strength wet and dry are all usehil tests that can be done in a cursory examination. A more critical identification can be made by a set of simple manual procedures based on burning, staining, solubiUty, density deterrnination, and microscopical examination. 

Filament. Eully drawn flat yams and partially oriented (POY) continuous filament yams are available in yam sizes ranging from about 3.3—33.0 tex (30—300 den) with individual filament linear densities of about 0.055 to 0.55 tex per filament (0.5—5 dpf). The fully drawn hard yams are used directly in fabric manufacturing operations, whereas POY yams are primarily used as feedstock for draw texturing. In the draw texturing process, fibers are drawn and bulked by heat-setting twisted yam or by entangling filaments with an air jet. Both textured and hard yams are used in apparel, sleepwear, outerwear, sportswear, draperies and curtains, and automotive upholstery. 

Metal-Matrix Composites. A metal-matrix composite (MMC) is comprised of a metal ahoy, less than 50% by volume that is reinforced by one or more constituents with a significantly higher elastic modulus. Reinforcement materials include carbides, oxides, graphite, borides, intermetahics or even polymeric products. These materials can be used in the form of whiskers, continuous or discontinuous fibers, or particles. Matrices can be made from metal ahoys of Mg, Al, Ti, Cu, Ni or Fe. In addition, intermetahic compounds such as titanium and nickel aluminides, Ti Al and Ni Al, respectively, are also used as a matrix material (58,59). P/M MMC can be formed by a variety of full-density hot consolidation processes, including hot pressing, hot isostatic pressing, extmsion, or forging. 

In aerospace appHcations, low density coupled with other desirable features, such as tailored thermal expansion and conductivity, high stiffness and strength, etc, ate the main drivers. Performance rather than cost is an important item. Inasmuch as continuous fiber-reinforced MMCs deUver superior performance to particle-reinforced composites, the former are ftequendy used in aerospace appHcations. In nonaerospace appHcations, cost and performance are important, ie, an optimum combination of these items is requited. It is thus understandable that particle-reinforced MMCs are increa singly finding appHcations in nonaerospace appHcations. 

The majority of spunbonded fabrics are based on isotactic polypropylene and polyester (Table 1). Small quantities are made from nylon-6,6 and a growing percentage from high density polyethylene. Table 3 illustrates the basic characteristics of fibers made from different base polymers. Although some interest has been seen in the use of linear low density polyethylene (LLDPE) as a base polymer, largely because of potential increases in the softness of the final fabric (9), economic factors continue to favor polypropylene (see OlefinPOLYMERS, POLYPROPYLENE). 

Static electrification may not be a property of the basic stmcture, but of a new surface formed by a monomolecular layer of water (82). All textile fibers at a relative humidity, at which a continuous monomolecular layer is formed, actually do have the same charge density. This is attributed to the absence of ionic transport which caimot occur in a monomolecular layer. At higher moisture levels than required to form a monomolecular layer, ionic conductivity can occur because of excess water molecules and by hydration of the ions. At very low moisture-regain levels, all materials acquire the same charge (83). 

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