Fiber braided/directional

Fiber braided/directional Weaving fibers into a tubular shape. As an example, A8cP Technology, Cincinnati, OH, specializes in developing braided reinforcements using a variety of material types, braid forms, and braid architectures for applications ranging from prostheses to... 

The reinforcement type and form chosen (woven, braided, chopped, etc.) will depend on the performance requirements and the method of processing the RP (Fig. 6-15). Fibers can be oriented in many different patterns to provide the directional properties desired. Depending on their packing arrangement, different reinforcement-to-plastic ratios are obtained (Appendix A. PLASTICS TOOLBOX). 

Nylons belong to the class of polymers known as engineering polymers that is, they are strong, tough, and heat resistant. We can readily extrude and mold nylons to form a wide variety of useful objects, such as tubing, furniture casters, and automotive air intake ducts. Nylons are commonly spun into filaments or fibers. These can be used directly, or braided, or twisted to form threads, yarns, cords, and ropes, which may be further woven to make fabrics. In their fibrous forms, nylons are used in carpets, backpacks, and hosiery. 

In a multifilament yam or in a braided fabric, normal (i.e. in the radial direction) frictional force holds the fibers together. Such an interfiber friction is desirable if we wish to have strong yams and fabrics. However, there eire situations where we would like to have a smooth fiber surface. For example, in a yam passing round a guide, a smooth fiber surface is desirable. If the fiber surface is... 

Fabrication of CC begins after the PAN fiber stabilization step. With the stabilized fiber a spun yam is formed. The yam is put in a stretch-breaking machine, of common use in the fabric industry, which produces a fiber tow of certain lengths in a continuous way. The yam is then homogenized with the use of different machines and subsequently braided or directly weaved. Once the cloths are ready, they are heated between 1,000 °C and 2,500 °C (carbonization or graphitization) under an inert atmosphere. As for the CP, the final temperature and heating rate will depend on the desired properties [99, 100]. 

Figure 21.2 Interaction of textile technology and composite engineering to form rigid fiber assemblies. Source Reprinted with permission from Hearle JWS, Du GW, J Text Inst, 81(4), 1980. (a) Knitted stmchire with repeated reversal of yam directions, (b) Simple plain weave fabric with threads continuous in X and Y directions, (c) Triaxial weave fabric, (d) Braid with yams at 9 to axis, (e) Triaxial braid. Copyright 1980, The Textile Institute.

Four-dimensional braid n. A type of braided reinforcement used to achieve specially directed strength and resistance to interlaminar shear, often involving mixed fibers of different materials. 

Multilayer fabric n. A fabric for reinforced-plastic structures formed by braiding to and fro or overlapping in one direction. Layers may be biaxial or triaxial, fibers mixed, and braid angles varied. 

RIM molders n. Molders for reaction injection molding (RIM). These types of molders are lightly constructed machines and consists of preformer, clamp, metering unit and mixhead. The preformer types include thermoforming, fiber-directed, knitting, braiding, or a combination of two or more. Herman F Mark (2003) Encyclopedia of Polymer Science and Technology, John Wiley and Sons, New York. 

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. 

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. 

A liber or a filament (a continuous form of fiber) is the fundamental unit of textile materials. It has a unique combination of high strength (tensile, bending, torsional, or compression), high flexibility (i.e., low modulus), extensibility, and shows recoverability on deformation. Most of these properties are observed in one principal direction, which is known as the axis of the fiber. Since all textile structures from one to three dimensional (yam, fabric, or braids, etc.) are built using this basic structural unit, these stmctures also possess the above unique properties. 

Three-Dimensional Braid (3-D braid) A recent development in building reinforcement performs for complex shapes that permits the placing of reinforcing fibers in three orthogonal (or nonorthogonal) directions so as to best support multidirectional stresses expected to act on the finished part in service. 

It is reported that no visible damage to the nanotube yams is imparted by the braiding process and the 3-D braids are very fine, extremely flexible, hold sufficient load, and are well suited for the use in any other textile formation process, or directly as reinforcement for composites. The reported elastic and strength properties of carbon nanotube composites so far are rather low in comparison with conventional continuous carbon fiber composites. It is believed that the properties can be substantially improved if the processing methods and stmctures are optimized [191]. 

In implant resistance welding, an electrically resistive element that is placed at the joint interface is heating by either direct or alternating current [2], The resistive implant may be as simple as a nichrome or stainless steel wire or mesh. More complex implants can be tapes of braided metallic wire with thermoplastic monofilaments or a composite of polymer matrix with electrically conductive particles or fibers. As shown in Fig. 26.26, during implant induction welding, the resistive implant is placed between the two parts. Electric current is then passed for a preset time through the resistance implant while the parts are under pressure. Then the current flow stops and the parts are kept under pressure while the weld cools, and the implant remains at the joint interface. 

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