Chopped carbon fibers

Carbon paper (CP) preparation begins by chopping carbon fibers obtained between 1,000 °C and 1,400 °C. Typical fiber diameter is between 5 and 15 pm. The porosity of the final product will depend on the length of the chopped fibers short fibers will render a small pore size. The chopped fibers are soaked in water and a binder. 

Hot working a mixture of metal powders and chopped carbon fiber... 

Furukawa [55] found that effective reinforcement was obtained with 2-4 vol% of chopped carbon fiber, whereas the same effect could be achieved with 0.3-0.5 vol% of continuous carbon fiber. 

DDL Chung and her research team at the State University of New York at Buffalo have investigated chopped carbon fiber reinforcements (5 mm) at volume fractions up to about 5% [2]. Two mixing approaches were used ... 

A chopped carbon fiber can be used as reinforcement, but in this form, it will be neeessary to form a mixture or slurry with the glass and the staple length must be < 3 mm, as otherwise, it will be hard to dissipate. When subjected to pressure in the consolidation process, there will be some fiber flow resulting in a more planar array. Continuous fiber can be adapted to more automated processes such as filament winding [83]. If a water based slurry proeess is used, it would be expected that a surface treated fiber should wet out more readily by achieving more efficient interfilament penetration of the matrix. 

Toutanji el al [239] and significantly enhanced the tensile strength properties of cementitious composites reinforced with a low fraction of chopped carbon fiber (YM 235 GPa and UTS 3.80 GPa). The values shown in Figure 20.50 compared favourably with predicted theoretical results based on the law of mixtures. 

Loop Tackle markets relatively cheap compression molded chopped carbon fiber fly reels, which are lightweight, with virtually zero thermal expansion and water absorption and excellent corrosion resistance to sea water. 

Carbon fiber has been found to be an effective thermistor [192-194], such as a cement paste reinforced with chopped carbon fiber (about 5 mm long) with silica fume (15 wt% cement). Its electrical resistivity decreased reversibly with increasing temperature (1-45°C), with activation energy of electrical conduction (electron hopping) of 0.4 eV. This value is comparable to semiconductors (typical thermistor materials) and is higher than that of carbon fiber polymer matrix composites. The current-voltage characteristics of carbon fiber reinforced silica fume cement paste were linear up to 8 V at 20°C. 

Good electrical conductivity at a lower loading level. CNT, CNF or GNP have proven to be an excellent additive to impart electrical conductivity in the nanocomposite at a lower loading level compared to carbon black, chopped carbon fiber or stainless steel fiber. 

Jacob G C, Starbuck J M, Fellers J F and Simunovic S (2005), Effect of fiber volume, fiber length and fiber tow size on the energy absorption of chopped carbon fiber-poljoner composites, Polym Compos 26 293-305. 

Thermoplastic Polymers. Thermoplastic polymers do not require a cure cycle but need only to be melted during processing (usually injection molding). The most common are nylon, polypropylene, and polyethylene which are usually molded with 10-25 vol.% discrete (chopped) carbon fibers. The addition of fibers substantially increases the modulus and, to a lesser degree, the strength. Electrical conductivity is also considerably increased and many applications of these composites are found in electromagnetic-interference (EMI) shielding. 

Figure 9.10. Tensile stress-strain curves of carbon-reinforced cement with various volume-fractions of chopped carbon fibers.

Polyethertherketone (PEEK) is a member of the polyaryletherketone (PAEK) family. PEEK possesses excellent chemical and thermal resistance, and its biocompatibility, mechanical wear characteristics and stability under gamma irradiation makes it a good candidate material for orthopaedic implants. PEEK is a relatively ductile material, with a flexural modulus and ultimate tensile strength higher than that of UHMWPE or PMMA. For some applications, chopped carbon fibers are added to reinforce the PEEK material, further increasing it stiffness and strength [29,30]. 

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