Fiber mechanical property

Sometimes, mechanical properties of polymer fibers can be found as an example, tenacity (tensile strength, in MPa) and tensile modulus (in GPa). It should be clear that these values cannot be used for design calculations unless the fibers are kept in their original form. The fibers display such high mechanical properties because of the high degree of orientation of the polymer chains in the fiber. The influence of the polymer type apparently is of secondary importance and only becomes important when the material is melted again. 

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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... 

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... 

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. 

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

Among the wide variety of ladder- or ladderlike polymers described in the literature, which are aimed at enhancing the thermal stability rather than at superior fiber mechanical properties [21, 22, 35], the benzazole polymers of the so-called PBZ family have attained a semicommercial status as high performance fibers processed via a liquid crystalline solution. A series of papers describing various aspects of these polymers appeared some time ago [23-30] and an excellent and comprehensive review appeared recently [31]. 

Ferreira AS, Monteiro SN, Lopes FPD et al. (2009) Curaua fiber mechanical properties evaluation by the Weibull analysis (in Portuguese). In Proceedings of 64 rd international... 

Neat polyester composite showed tensile strength around 41 MPa, Young s modulus around 9.68 GPa, and flexural strength around 61 MPa. After reinforcement with fiber, mechanical properties were enhanced and some of the important properties are explained below. Singh et al. [102] reported that sisal-polyester composites from nonwoven sisal mats with fiber content 50% by volume showed a tensile strength of 30 MPa and a tensile modulus of 1.15 GPa. The composites were manufactured by impregnation of the nonwoven sisal mats under compression molding for 2 hrs [9, 102]. 

The results presented in this chapterfocus on properties in terms of the physical and chemical structure of palm and pineapple fibers, mechanical properties, processing behavior and final properties of these fibers with thermoplastics matrixes, paying particular attention to the use of physical and chemical treatments for the improvement of fiber-matrix interaction. 

It has been demonstrated that there is a direct relationship between the fiber mechanical properties and the molecular orientation (Figure 1). A similar relationship exists between the processing conditions, molecular orientation and mechanical properties. It has been shown that a combination of optical birefringence and the infrared spectroscopy techniques can be used for the measurement of molecular orientation. The results show that for a set of fiber samples, the 841 cm" infrared peak can be confidently used for the estimation of crystalline orientation averages. The 973 cm" peak can be separated using curve fitting procedures into 972 and 974 cm" components and the latter component can be used to estimate the amorphous orientation averages. 

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