Mechanical properties carbon fiber reinforcement

Most recent studies (69) on elevated temperature performance of carbon fiber-based composites show that the oxidation resistance and elevated temperature mechanical properties of carbon fiber reinforced composites are complex and not always direcdy related to the oxidation resistance of the fiber. To some extent, the matrix acts as a protective barrier limiting the diffusion of oxygen to the encased fibers. It is therefore critical to maintain interfacial bonding between the fiber and the matrix, and limit any microcracking that may serve as a diffusion path for oxygen intmsion. Since interfacial performance typically deteriorates with higher modulus carbon fibers it is important to balance fiber oxidative stabiHty with interfacial performance. 

Poly[2,2 -(m-phenylene-5,5 -benzimidazole)] (PBI) is a very high glass transition temperature (Tg 430°C), commercially available material. It possesses excellent mechanical properties, but is difficult to process into large parts and has high moisture regain and poor thermo-oxidative stability at temperatures above approximately 260 °C. Polyimides, especially the thermoplastic polyimides, offer attractive thermo-oxidative stability and processibility, but often lack the thermal and mechanical characteristics necessary to perform in applications such as the matrix for high use-temperature (over 300 °C) structural composites (for example, carbon fiber reinforced) for aerospace use. The attempt to mitigate... 

Fig. 9. Effect of sub-Tg annealing on the ultimate mechanical properties of carbon-fiber-reinforced epoxies...

Figure 8. Mechanical properties of various carbon-fiber-reinforced composites compared to bone and some biomedical alloys (20). HM and HT refer, respectively, to fibers of high modulus and high tensile strength.

In order to improve the surface properties of carbon fibers without affecting the mechanical properties of the reinforcing fibers, various monomers, including pyrrole and carbazole, were used to electrograft conjugated copolymers and produce homogeneous and continuously coated carbon fiber surfaces <2001SM391>. 

FIGURE 12.11 Improvements of the mechanical properties of three-dimensional reinforced CMCs by hybrid infiltration routes (a) R.T. flexural stress-strain plots for a three-dimensional carbon fiber reinforced composite before and after cycles of infiltration (comparison between eight cycles with zirconium propoxide and fonr cycles pins a last infiltration with aluminum-silicon ester (b) plot of the mechanical strength as a fnnction of the final open porosity for composites and matrix of equivalent porosity, before and after infiltration (Reprinted from Colomban, R and Wey, M., Sol-gel control of the matrix net-shape sintering in 3D reinforced ceramic matrix composites, J. Eur. Ceram. Soc., 17, 1475, 1997. With permission from Elsevier) (c) R.T. tensile behavior (d) comparison of the R.T. mechanical strength after thermal treatments at various temperatures. (Reprinted from Colomban, R, Tailoring of the nano/microstructure of heterogeneous ceramics by sol-gel routes, Ceram. Trans., 95, 243, 1998. With permission from The American Ceramic Society.)... 

In general, polymers have low stiffness and strength in comparison with other materials, e.g., metals and ceramics, and consequently these materials present serious difficulties in structural applications. To improve their mechanical properties, polymers are reinforced by the addition of rigid particles or fibers to form composite materials (1). Thus, polymer matrix composite materials are made up of a low modulus phase, the polymer matrix, and a high modulus phase, the reinforcement, which is usually carbon or glass. The modulus of the composite is higher than that of the polymer matrix, and the increment is proportional to the volume fraction of the reinforcement. In general, the properties of the composite depend not... 

S. P. Saha, Mechanical properties of machine-mixed carbon fiber reinforced bone cement, ASME. Appl. Mechanics Div. 21. 57-60, 1985. 

Table I shows the mechanical properties of the carbon fiber-reinforced PTFE (PTFE composite non-crosslinked) and the carbon fiber-reinforced PTFE with fluorinated-pitch (PTFE / FP composite thermo-chemical crosslinked). For the tensile test with a direction of 45 ° for plane-woven carbon fabric, the tensile strength of the PTFE / FP composite was about 2.3 times higher than that of the non-crosslinked PTFE composite. Moreover, the Young s modulus of the crosslinked composite was about 2.6 times higher than that of the PTFE composite. The tensile strength and Young s modulus are results of 0 ° or 90 ° direction for the fabric reflected the carbon fiber strength and the modulus.

The findings of the study by Kyomoto et al. [22] have been extended to include carbon-fiber-reinforced PEEK as a substrate material [23], Moreover, electron spin resonance was used to characterize radical formation upon irradiation with UV light, indicating that a steady state in radical creation was already reached after 15 min of illumination. Again, graft layers of PMPC were produced with the aim to improve the durability of an artificial hip. The gravimetric wear tested under realistic conditions was significantly decreased for PMPC-modified PEEK surfaces, whereas the bulk mechanical properties of the material were shown to be unaffected. 

TABLE 39.7 Mechanical Properties of Carbon Fiber-Reinforced... 

S-H. Wu, F-Y. Wang, C-C.M. Ma, W-C. Chang, C-T. Kuo, H-C. Kuan, and W-J. Chen, Mechanical, thermal and morphological properties of glass fiber and carbon fiber reinforced polyamide-6 and polyamide-6/clay nanocomposites, Mater. Lett., 49, 327-333 (2001). 

Carbon fiber-reinforced PAs may be used for conductive and electrical shielding applications where high mechanical properties are also required, and for applications requiring a measure of internal lubrication, slip and good wear-resistance. Mineral-reinforced PA (with talc or mica) offers very good dimensional stability, and low shrinkage and warpage. 

Plastics (thermoplastics, duroplastics, elastomers) have been reinforced for decades to enhance mainly mechanical properties with fibers (glass, carbon, aramide, metal, ceramic, natural). 

Abu Abu Bakar, M. A., Ahmad, S., Kuntjoro, W. Effect of matrix modification on the mechanical properties of short carbon fiber-reinforced epoxy composites. J. Reinforced Plast. Compos. 30 (2011) 357-361. 

CFRPs are strong and light fiber-reinforced polymers. Carbon fibers are a new breed of high-strength materials. Carbon fiber contains at least 90% carbon prepared by controlled pyrolysis of rayon fibers [34]. The subsistence of carbon fiber came into use in 1879 when Edison took a patent for the fabrication of carbon filaments used in electric lamps [35]. The composites manufactured using carbon fiber reinforcements exhibit a range of mechanical properties suitable for many constructional, industrial, and automobile applications. 

Shen, L., Yang, H., Ying, J., Qiao, F, and Peng, M. (2009) Preparation and mechanical properties of carbon fiber reinforced hydroxyapatite/polylactide biocomposites. J. Mater. Sci. - Mater. Med., 20 (11), 2259-2265. 

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