Hybrid braids

Essentially, the production of hybrid braids is based on the presence of isolation tracks and columns. These isolation tracks and columns lead to a change in the... 

Bradford, P.D. and Bogdanovich, A.E. Electrical conductivity study of carbon nanotube yarns, 3-D hybrid braids and their composites. XCom os aterT Q 42(15), 1533-1545. 

The available forms of reinforcement follow terminology and technology borrowed from the textile industry. The basic forms described throughout this chapter and other chapters for glass and other fibers including hybrid mixtures are summarized in this chapter. They are continuous filament, woven fabrics, nonwoven fabrics, knitted fabrics, braids, and tapes. 

Milwich et al. (2006) combined ideas of cellulose fiber orientation in wood with the structure of the stem of giant reeds to create a hybrid model realized using advanced braid protrusion machinery at the Institute of Textile Technology and Process Engineering (ITV) Germany. The outcome called Technical Plant Stem is a commercially scalable architectural textile composite that demonstrates excellent strength and impact resistance with the minimal material use (Speck and Speck, 2006). 

Ultrapure silica or quartz fibers are used in fabrics, yams, rovings and threads. Fabrics are used to reinforce radomes, antenna windows for missiles, high temperature circuit boards, and rocket nose cones. Braided yarns provide high temperature electrical insulation, e.g., for coaxial cables, thermocouple wires, and space separators. Rovings are used to reinforce polymer matrix composites for ablative and electrical uses, as well as high performance sporting goods, e.g., tennis racquets and skis, especially when hybridized with carbon fibers. Threads are used to stitch cable tray insulation for nuclear power plants. 

Another way to interpret this localization process is via a Pauling s hybridization approach, where we consider each M-L braid as an overlap between a metal hybridized orbital and a localized ligand orbital. As seen in Fig. 4, we can hybridize the valence atomic orbitals on the metal center into orbitals that are localized on each M-L axis [25]. These hybridized orbitals can then overlap with the corresponding locahzed ligand orbitals (Fig. 2, right-hand side) to form the six M-L bonds. 

The track-and-column braiding process has been used to produce braids with a solid, rectangular cross section. The production of solid braids with more complex crossshape geometry can be achieved through juxtaposition of multiple braids with rectangular cross sections. Additional fibre placements within the cross section allow certain yams to braid within specific area of the cross section only to produce a hybrid composite (Kostar and Chou, 2002 Ko et ah, 1989 Kamiya et ah, 2000). 

The cross section of hybrid 3D braids is characterized by the grouping of specific yams within a desired partial area of the cross section (Kostar, 1998). 

This effect also can be seen when applying reinforcement fibers which are not orientated in process direction. Thus, wound or braided fibers in any fiber orientation between 0° and 90° should be covered by unidirectional fibers in process direction. Otherwise, the fibers will be warped during the process, which reduces the product s quality and furthermore can lead to process interruption. The processability of profiles with sharp edges is also limited due to the minimum bending radius of the circumferential reinforcement fibers. In order to meet special performance requirements, it is possible to apply hybrid mixtures of the reinforcing materials. Table 8.1 gives a short overview on properties of reinforcement materials. 

Wan Y Z, Wang Y L, He F, Huang Y, Jiang H J (2007) Mechanical performance of hybrid bismaleimide composites reinforced with three-dimensional braided carbon and Kevlar fabrics . Composites Part A, 38, 495-504. 

Figure 2.2 Three typical structures of hybrid polymer-metal yams (a) metal-core yams, (b) polymer-core yams, and (c) polymer-metal braided yams. (Polymer fibers are shown in red, while metallic fibers are shown in gray.)...

FIGURE 7.5 (a) Schematic of 3-D woven fabric incorporating very fine CNT yam as through thickness (Z) reinforcement (b) Schematic of square 3-D braided hybrid preform with large axial fiber bundles and very fine CNT off-axis braided yams... 

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