Braided fabrics structures

Figure 2.6 Schematic of a braided fabric structure in relaxed and stressed conditions.

Due to the complex nature of the textile reinforcement since air can become entrapped in the interstices of the fabric structure. This can be particularly evident when coarse yams (or tows) are used or in complex three-dimensional (3-D) stmctures, e.g. braided or woven, and may be most prevalent at the tool/composite interface. 

Woven, knitted and braided fabrics for medical textile products are made from yarns that contain fibers, whereas nonwoven fabrics can be made directly from fibers or even polymers. Expanded PTFE fabrics and electrospun webs of micro and nano denier fibers, used in medicine, are examples of products made directly from polymers. All fabrics mentioned vary widely in their construction parameters and, therefore, in the performance characteristics obtained from a given raw material. There is, therefore, a hierarchy of structure. The performance of a final product can be modified from two to four levels of organization. 

Nonwovens are structures of textile materials, such as fibres, continuous filaments, or chopped yarns of any nature or origin, that have been formed into webs by any means, and bonded together by any means, excluding the interlacing of yams as in woven fabric, knitted fabric, laces, braided fabric or tufted fabric. 

Various textile structures can be employed to design a garment for embedded wearable technology. Fabric structures such as woven, knitted, braided, non-woven and other textile stmctures are possible, depending on the requirements of the system. Each type of system has its unique properties that can play a major role in the functionality of the system. Most of these types of textile structures are used for electronic textiles, such as embroidery and others. Nevertheless, these structures find uses in many smart textiles used today. 

D reinforcing products mats, woven or knitted fabrics, braidings from yarns or rovings. 3D reinforcing structures. 

In the last 10 years, significant advances in fibrous monolithic ceramics have been achieved. A variety of materials in the form of either oxide or nonoxide ceramic for cell and cell boundary have been investigated [1], As a result of these efforts, FMs are now commercially available from the ACR company [28], These FMs are fabricated by a coextrusion process. In addition, the green fiber composite can then be wound, woven, or braided into the shape of the desired component. The applications of these FMs involve solid hot gas containment tubes, rocket nozzles, body armor plates, and so forth. Such commercialization of FMs itself proves that these ceramic composites are the most promising structural components at elevated temperatures. 

Manufacturers of composite structures have traditionally used prepreg tape to manufacture structural components. Fibres are initially combined into unidirectional tows (bundles) of fibres combined into fabrics, e.g. by weaving or knitting. The vast majority of the tows employed in woven, braided or knitted reinforcements comprise low twist or untwisted continuous filament yams. Three-dimensional technical textiles can be produced by weaving [5], knitting [6] and braiding [7] or as non-crimp fabrics. 

Braids Is used to give high strength three-dimensional (3-D) reinforcement, incorporating more than one type of fiber, if required. Conventional woven fabrics are limited to providing reinforcement at orthogonal orientations, but many reinforced plastics structures are loaded in non-orthogonal fashion. Woven fabrics are, therefore, not necessarily mechanically efficient. 

Of the available textile reinforcements (woven, braided, knitted, stitched), many can now be considered to be mature applications. For example, non-crimp fabric (carbon fibre) is used to manufacture the A380 rear pressure bulkhead at 240kg, in mass, 6.2m long, 5.5m wide, and 1.6m deep, this can be classed as a large structure at a smaller length scale, braided carbon fibres are now used regularly for high performance bicycle frames. 

A variety of shapes can be fabricated for composite applications, from hollow tubular (with in-laid, non-interlaced yams) to solid sections, including I-beams. Unlike woven fabrics, braided structures can be directly laid on a three-dimensional mandrel by passing it through the braiding ring (Fig. 1.6) and hence producing seamless, near-net shapes. For example, aircraft propeller blades are produced by using this... 

The strength and tensile behavior, at room and high temperatures, as well as the structure of three dimensional earbon fiber/SiC composites, fabricated by the slurry pulse/CVI combined process, were eharacterized by Suzuki et al [207-209]. Carbon fiber preforms, constructed with 4-step braid, 4-step/axial braid, 2-step braid and orthogonal weave, were used as reinforcements of the composites. The composites were fabrieated by a process consisting of slurry and dissolved organosilicon polymer infiltrations, followed by the application of pulse CVI. 

Fujita A, Hamada H, Maekawa Z, Uozumi T, Okauji T, Ohno E, I-beam composites with three-dimensional braiding structure- fabrication and mechanical properties. Proceedings, TexComp-2, Leuven, Belgium, May 17-19, 1994. 

Kostar TD, Chou TW, Design and automated fabrication of 3-D braided preforms for advanced structural composites, Computer Aided Design in Composite Material Technology III, Elsevier Science, 63-78, 1992. 

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