Randomly oriented fiber

Figure 5 Schematic representation of (a) aligned and (b) randomly oriented fiber reinforced composites.

In nonwoven geotextiles, the fibers are much thinner but far more numerous. The various types are needle-punched, resin-bond, and melt-bond. All contain a labyrinth of randomly oriented fibers that cross one another so that there is no direct line of flow. The fabric must have enough open space to allow liquid to pass through, while simultaneously retaining any upstream movement of particles. The needle-punched nonwoven type is very commonly used as a filter material. 

Nonwovens are textile products that are manufactured directly from fibers. They are defined as a manufactured sheet, web, or matt of directionally or randomly oriented fibers, bonded by friction, and/or cohesion, and/or adhesion excluding paper and products which are woven, tufted, stichbounded incorporating binding yams or filaments, or felted by wetmilling whether or not additionally needed. The fibers may be of natural or manmade origin. They may be staple or continuous filaments or maybe formed in situ. ... 

Toughness theories for short and randomly oriented fiber composites... 

Fig. 6.7. A model for plastic bending of fiber and fragmentation of matrix during fracture of randomly oriented fiber composites. After Helfet and Harris (1972) and Hing and Groves (1972).

One efficient removal procedure is to use a 0.45- m filter. There are basically two types of filters depth and screen. Depth filters are randomly oriented fibers that will retain particles throughout the matrix rather than just on the surface. They have a higher load capacity than screen filters. Due to the random nature of the matrix, they have no definite upper-limit cutoff particle size retained. Their porosity is identified as a nominal pore size to indicate this variable. 

Mineral fibers for the production of insulating materials are named after their. starting materials as glass or rock fibers and as refractory ceramic fibers. The names mineral, glass or rock wool are usually used, since they, in contrast to textile glass fibers, are produced as short, randomly oriented fibers. The end products are therefore known as mineral wool insulation materials. 

Glass-mat reinforced thermoplastic (GMT) is similar to SMC and is available in sheet form, reinforced with random oriented fibers that may be continuous or discontinuous. It is manufactured on a double belt press where the glass fiber mats are sandwiched between layers of extruded molten polymer before it enters the press. The thermoplastic is usually about a few millimeters thick and thus stiff, and hence stored as fiat sheets. Another method involves deposition of a molten mixture of resin, chopped fibers, and additives over a moving belt where the water is driven off. The fiber volume fraction in this compound is usually 0.1-0.3 and fiber lengths are in the range of 10-30 mm, unless the reinforcement is continuous. 

Fig. 8 Left-. C2C12 cells were seeded on aligned and randomly oriented fibers and on a glass control. Confocal images taken at 30 min, 60 min, 2 h, 5 h, and 24 h after seeding are shown, with increasing time from top to bottom. Actin is stained green and nuclei are stained blue. Scale bar. 25 pm. Right Quantification of cell aspect ratio is shown for all time points. All data sets are significantly different from each other except those indicated by NS [52]...

With the exception of glass and mineral fiber products, and, like rubbers and plastics, textiles are largely hydrocarbon polymers and as such have a strong tendency to ignite and burn from a small flame. Textiles are essentially sheets of woven, knitted, or sometimes randomly orientated fibers and may be directly used on their own or in combination with other materials, e.g., coated fabrics, or as reinforcement, e.g., in rubber hoses. Other examples of textile products are upholstered furniture and protective clothing. 

Kitano, T. Nagatsuka, Y. Lee, M Kimijima, K Oyanagi, Y. (1994). A Method for the Production of Randomly Oriented Fiber Reinforced Thermoplastic Composites and Their Mechanical Properties. Seikei-Kakou (the Journal of Japanese Society of Polymer Processing, in Japanese), Vol.6, No.l2, pp. 904-915 ISSN 0915-4027... 

It may be recalled from earlier discussions that an equation of this form corresponds to an upper bound to a composite modulus (Section 12.1.1.1). Thus, particulate fillers tend to yield lower-bound values, as predicted by relationships such as Kerner s (1956b), while long, oriented fibers tend to yield upper-bound values of modulus. Short, randomly oriented fibers tend to yield intermediate behavior, but, as pointed out by Brody and Ward (1971), usually lead to moduli closer to the lower than to the upper bound, depending on the modulus of the polymer. On the other hand, Lavengood and Gulbransen (1969) reported moduli closer to upper-bound values for short fibers dispersed in an epoxy resin. 

For two-dimensional randomly oriented fibers in a composite, approximating theory of elasticity equations with experimental results yielded this equation for the planar isotropic composite stiffness and shear modulus in terms of the longitudinal and transverse moduli of an identical but aligned composite system with fibers of the same aspect ratio ... 

Both fillers, for aspect ratios sufficiently high, have similar levels of ultimate reinforcement, reaching the same plateau, which corresponds to the rule of mixtures (horizontal solid lines). However fiber-like fillers approach maximum reinforcement already for aspect ratios of 100, while platelet-like fillers need aspect ratios higher than 2000. It can therrfore be concluded that, in the imidirectional case, fibers are more effective than platelets. This is, however, different for the situation of randomly distributed fillers. Figure 12.3b shows the reinforcement of 3D randomly oriented fiber-like and platelet-like fillers, of different aspect rahos, in a polypropylene (PP) matrix. The observation that fiber fillers reach the maximum reinforcement for aspect ratios much smaller than those necessary in the case of platelet filler shll holds. This effect is also more prominent since randomly distributed platelets need an aspect ratio of 10,000. Nevertheless, the plateau relative to platelet fillers is twice as high as for fibers filler. It can therefore be concluded that, in the case of randomly oriented filler, platelets are more effective than fibers but only for aspect ratios higher than 100. 

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