Composite fibers fabrication

Fig. 2.11 Electrospinning and hot-pressing of metal oxide materials, (a) SEM image of the as-spun TiOj/PVAc composite fibers fabricated by electrospinning from a DMF solution, (b) SEM image of TiOj/PVAc composite fibers after hot-pressing at 120 °C for 10 min. (c) SEM image of unpressed TiO nanofibers after caicination at 450 °C. (d) SEM image of hot-pressed TiOj nanofibers after calcinations at 450 °C (Reprinted with permission from Kim et al. 2006, Copyright 2006 American Chemical Society)...

Low density, carbon fiber-carbon binder composites are fabricated from a variety of carbon fibers, including fibers derived from rayon, polyacrylonitrile (PAN), isotropic pitch, and mesophase pitch. The manufacture, structure, and properties of carbon fibers have been thoroughly reviewed elsewhere [3] and. therefore, are... 

Resin with an accelerator added but not catalyst. According to ASTM, those plastics having superior properties over those consisting of the base resin, due to the presence of high-strength fillers embedding in the composition. Reinforcing fillers are fibers, fabrics or mats made of fibers. 

SCRIMP process This Seeman Composites Resin Infusion Process (SCRIMP) is described as a gas-assist resin transfer molding process. As an example glass fiber fabrics/ thermoset vinyl ester polyester plastic and polyurethane foam panels (for insulation) are placed in a segmented tool. A vacuum is pulled with a bag so that a huge amount of plastic can be drawn into the mold (Marco process approach). Its curved roof is made separately and bonded to the box with mechanical and adhesive fastening. It is similar to various reinforced plastics molding processes. 

Ceramic matrix composites are produced by one of several methods. Short fibers and whiskers can be mixed with a ceramic powder before the body is sintered. Long fibers and yams can be impregiated with a slurry of ceramic particles and, after drying, be sintered. Metals (e.g., aluminum, magnesium, and titanium) are frequently used as matrixes for ceramic composites as well. Ceramic metal-matrix composites are fabricated by infiltrating arrays of fibers with molten metal so that a chemical reaction between the fiber and the metal can take place in a thin layer surrounding the fiber. 

Experimental results are presented that show that high doses of electron radiation combined with thermal cycling can significantly change the mechanical and physical properties of graphite fiber-reinforced polymer-matrix composites. Polymeric materials examined have included 121 °C and 177°C cure epoxies, polyimide, amorphous thermoplastic, and semicrystalline thermoplastics. Composite panels fabricated and tested included four-ply unidirectional, four-ply [0,90, 90,0] and eight-ply quasi-isotropic [0/ 45/90]s. Test specimens with fiber orientations of [10] and [45] were cut from the unidirectional panels to determine shear properties. Mechanical and physical property tests were conducted at cold (-157°C), room (24°C) and elevated (121°C) temperatures. 

Chemical Vapor Infiltration (CVI). Recall from Section 3.4.2 that CVI is primarily nsed to create ceramic matrix composites, CMCs. Fabrication of CMCs by CVI involves a sequence of steps, the first of which is to prepare a preform of the desired shape and fiber architecture. This is commonly accomplished by layup onto a shaped form of layers from multifilament fibers using some of the techniques previously described, such as filament winding. 

Composite components, both fiber (or adherend) and matrix, have chemical, morphological and structural variability that can be operative at or near surfaces to form an interphase. Bulk characterization of these materials ignores these components because of the dilution of their effect in the bulk. However, when composites are fabricated, fiber to fiber distances are on the order of tenths of microns. Interphase structures are also on the order of tenths of microns and can be a significant proportion of the structure of the material between fibers. 

Both fiber-matrix interphase-sensitive mechanical tests (interlaminar shear strength, 90° flexure) and interphase-insensitive tests (0° flexure) were conducted on high volume composite samples fabricated from the same materials and in the same manner as discussed above to see if the interphase and its properties altered the composite mechanical properties and in what manner. A summary of the data is plotted as a bar graph in Fig. 7. The first set of bars represents the difference in fiber-matrix adhesion measured between the bare fibers and the sized fibers by the ITS. The composite properties plotted on the figure also show increased values for the epoxy-sized material over the bare fiber composite. 

Ultra-high modulus fibers such as aramid and carbon fibers have been currently utilized for composite material fabrication. Ultra-high modulus polyethylene (UHMPE) fiber is also applicable for composite fabrication because of the light weight in addition to its high modulus, vibration damping, and resistance to chemicals. However, this fiber has drawbacks such as poor interfacial adhesion with the polymer matrix of the composite because of highly hydrophobic nature of the fiber surface. 

In Sections 24.3 and 24.5 the flammability and fire resistance of individual fiber/fabric type are discussed. However, as also discussed before, the fire resistance of a fabric not only depends upon the nature of components and the FR treatments applied, but also on fabric area density, construction, air permeability, and moisture content. Nonwovens, for example, will have superior properties to woven or knitted structure, even if all other variables are kept the same.93 The air entrapped within the interstices of any fabric structure and between layers of fabrics within a garment assembly provides the real thermal insulation. For effective thermal and fire resistance in a fabric structure, these insulating air domains need to be maintained.22 In general, for protective clothing and fire-block materials, for best performance multilayered fabric structures are employed. The assembly structures can be engineered to maximize their performance. It is beyond the scope of this chapter to go into details of these composite structures hence the reader is referred to the literature on specified applications and products available. 

Figure 31. Weight-loss of unidirectional carbon/carbon composites by isothermal oxidation in air, as affected by Zn2 207 inhibitor or by SiC coating (32,49) The composites were fabricated with 50 vol.-% high-modulus Modmor I fibers, coal-tar pitch as matrix precursor, four densification cycles, and final heat treatment to 1400°C.

Figure 34. Comparison of the flexural strengths of unidirectional carbon/carbon composites (left-hand side) with those of hybrid composites in which the final impregnation is made with an epoxy resin (34) The composites were fabricated with high-modulus fibers rigidized with phenolic resin, and subjected to four densification cycles with coal-tar pitch plus sulfur.

The need to develop fibers with better microstructural stability at elevated temperatures and ability to retain their properties between 1000-2000°C. The requirements of fiber properties for strong and tough ceramic composites have been discussed by DiCarlo.83 A small diameter, stoichiometric SiC fiber fabricated by either CVD or polymer pyrolysis, and a microstructur-ally stable, creep-resistant oxide fiber appear to be the most promising reinforcements. 

This chapter reports the study of the chemical composition of the polysulfide fraction in dicyclopentadiene and styrene modified materials, the mechanical properties of modified materials, and their use in the preparation of composite materials by the impregnation of polypropylene and glass-fiber fabrics. 

Carbon materials are widely used in industry in form offor example, porous powders, fibers, fabrics, pellets, extrudates or composites for very different purposes. This is because carbon materials can, depending on their structure, exhibit very different properties. 

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