Fibers mechanics

It is difficult to determine the cross-sectional area of a fiber. Direct observation and measurement of a cross section under a microscope is the most accurate method (15). This is a destmctive test that does not allow subsequent study of fiber mechanical properties, and is slow and tedious. Also, it does not take into account any variations in the cross-sectional area along the fiber length. Measurement of fiber diameters from microscopic observations of longitudinal views is somewhat easier, but the eUipticity of the cross section in certain fibers can lead to serious errors. 

Normalised fiber mechanical properties are expressed in terms of unit linear density. For example, in describing the action of a load on a fiber in a tensile test, units of N/tex or gram force per denier (gpd) are generally used. If this is done, the term tenacity should be used in place of stress. The tme units of stress are force per unit cross-sectional area, and the term stress should be reserved for those instances where the proper units are used. 

A schematic stress-strain curve of an uncrimped, ideal textile fiber is shown in Figure 4. It is from curves such as these that the basic factors that define fiber mechanical properties are obtained. 

Olefin fibers are used for a variety of purposes from home furnishings to industrial appHcations. These include carpets, upholstery, drapery, rope, geotextiles (qv), and both disposable and nondisposable nonwovens. Fiber mechanical properties, relative chemical inertness, low moisture absorption, and low density contribute to desirable product properties. Table 7 gives a breakdown of olefin fiber consumption by use (73—75). Olefin fiber use in apparel... 

It is difficult to process HPPE staple fibers mechanically because of so-called married fibers which are bundles of 4—6 fibers that firmly adhere to each other and resist separation by conventional processing. Although HPPE fibers like to adhere to each other, they exhibit poor adhesion to other materials. 

The tensile and flexural properties as well as resistance to cracking in chemical environments can be substantially enhanced by the addition of fibrous reinforcements such as chopped glass fiber. Mechanical properties at room temperature for glass fiber-reinforced polysulfone and polyethersulfone are shown in Table 5. 

Nonoxide fibers, such as carbides, nitrides, and carbons, are produced by high temperature chemical processes that often result in fiber lengths shorter than those of oxide fibers. Mechanical properties such as high elastic modulus and tensile strength of these materials make them excellent as reinforcements for plastics, glass, metals, and ceramics. Because these products oxidize at high temperatures, they are primarily suited for use in vacuum or inert atmospheres, but may also be used for relatively short exposures in oxidizing atmospheres above 1000°C. 

Bianchi et al. (19) spun fibers from isotropic and anisotropic solutions of cellulose (D.P. 290) in LiCl (7.8%)-DMAC solutions. The fiber mechanical properties increased throimh the isotropic-anisotropic transition with elastic moduli as high as 22 GPa (161 g/d) being obtained. 

The hair shaft (Figure 6.1) comprises three main structures (1) the outer cuticle responsible for the main optical and frictional properties of the fiber (2) the cortex, responsible for the bulk fiber mechanical properties such as strength and flexibility and (3) the porous medulla, which is more prominent in gray hair, but otherwise may or may not be present. Cuticle thickness varies markedly between species. Though much of our understanding of hair structural biology is derived from the study of wool, this homologous... 

The microfibrils, which are 10-20 nm wide, are visible in the electron microscope without pretreatment. Microfibrils are combined to greater fibrils and lamellae, which can be separated from the fibers mechanically, although their dimensions greatly depend on the method used. 

Although the significance of fiber mechanical properties such as breaking and tearing strength, extensibility, and tenacity has been estab-... 

Boron fibers, like any CVD fiber, have inherent residual stresses which originate in the process of chemical vapor deposition. Growth stresses in the nodules of boron, stresses induced due to diffusion of boron into the W core, and stresses generated due to the difference in the coefficient of expansion of the deposited boron and the tungsten boride core, all contribute to the residual stresses, and thus can have a considerable influence on the fiber mechanical properties. 

In recent years, poly(p-phenylene benzobisoxazole) (PBO) fibers have become prominent in high strength applications such as body armor, ropes and cables, and recreational equipment. However, degradation of PBO fiber mechanical properties following exposure to moisture has been documented by the manufacturer (7) and at least one failure of PBO-based body armor in the field has occurred (2). The objectives of this study were to compare changes in mechanical and chemical properties of yams extracted from PBO-based body armor that was penetrated by a bullet in the field approximately 6 months after being deployed, with PBO-based body armor panels of the same model aged in the laboratory under elevated temperature and moisture conditions. 

Donaldson K, Brown RC, Brown GM. 1993. Respirable industrial fibers Mechanisms of pathogenicity. Thorax 48(4) 390-395. 

Anisotropic carbon fibers mechanical properties dependent upon the degree of orientation of the graphite strands in the direction of the fiber axis... 

Fulling. Fulling is a chemicophysical process in which the fabric is treated with acid or soap solutions on the fulling mill which works the fibers mechanically to felt them. 

In one study, newspaper was recycled without the use of water.77 The paper was fiberized mechanically, and the fibers were air-laid to produce a new sheet. It was necessary to treat the fibers first with ozone, then with ammonia to achieve good interfiber bonding when the air-laid sheet was pressed. The tensile strength of the resulting paper approached that of the original newsprint. Such a process would eliminate aqueous effluents. 

Figure 8-39. Electron micrograph of a hair fiber mechanically abraded by rubbing against another hair. Note cuticle abrasion and hair fragments.

Table 9 38 Different fibers mechanical and cost used in RPs ... 

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