Carbon fibers strength

For nosetip materials 3-directional-reinforced (3D) carbon preforms are formed using small cell sizes for uniform ablation and small pore size. Figure 5 shows typical unit cell dimensions for two of the most common 3D nosetip materials. Carbon-carbon woven preforms have been made with a variety of cell dimensions for different appHcations (27—33). Fibers common to these composites include rayon, polyacrylonitrile, and pitch precursor carbon fibers. Strength of these fibers ranges from 1 to 5 GPa (145,000—725,000 psi) and modulus ranges from 300 to 800 GPa. 

Fig. 6. Each of carbonization temperature on PAN-based carbon fiber strength and modulus (31). To convert GPa to psi, multiply by 145,000.

Jung, T., Subramanian, R.V. and Manoranjan, V.S. (1993). Prediction of fiber strength at the critical length A simulation theory and experimental verification for bimodally distributed carbon fiber strength. J. Mater. Sci. 28, 4489-4496. 

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.

Figure 3.21 Effects of various types of flaw on carbon fiber strength distributions (a) Original surface flaws ...

In a production process, this method is much preferred by the author. Takaku et al [90] stabilized a AN/MA precursor at 240, 255 and 270°C and observed an increase in oxidized density, which reached a constant value of 1.58 gcm at the longer stabilization times, obtaining optimum carbon fiber strength with an oxidized density of about 1.375 gcm (Figure 5.37). Bajaj and Roopanwal [91] attributed the increase in density to closer packing of molecular chains due to cyclization of the nitrile groups. 

A run-away exotherm occurred in one of the oxidation ovens and there was a rush of evolved gases, which dislodged the explosion relief blanket situated at the top of the oven. This accidental repositioning of the blanket was not noticed. However, it happened to coincide with an increase in the carbon fiber strength. Subsequently, a new permanent position was established for the blanket, to take advantage of this bonus in carbon fiber strength. 

A smoke pencil should be used to check for ingress of air. The furnace can be correctly balanced by adjusting the body flow of N2 at the furnace inlet end to such a level that, when looking down into the furnace muffle, the atmosphere is not entirely clear but, at the same time, smoke is not forced out from the outlet end. It is essential to maintain a slight cloudy atmosphere, as this permits the correct concentration of HCN to build up within the furnace, significantly improving the carbon fiber strength. 

Table 18.1 A random sample of 100 carbon fiber strengths (GPa) arranged in ascending order...

Reynolds, W.N. and Sharp, J.V. (1974) Crystal shear limit to carbon fiber strength. Carbon, 12 103-110. 

Thus far the importance of carbon cluster chemistry has been in the discovery of new knowl edge Many scientists feel that the earliest industrial applications of the fullerenes will be based on their novel electrical properties Buckminsterfullerene is an insulator but has a high electron affinity and is a superconductor in its reduced form Nanotubes have aroused a great deal of interest for their electrical properties and as potential sources of carbon fibers of great strength... 

Other reinforcements that may be used in the substrate layers of decorative laminates and throughout the stmcture of industrial laminates are woven fabrics of glass or canvas and nonwoven fabrics of various polymeric monofilaments such as polyester, nylon, or carbon fibers. Woven and nonwoven fabrics tend to be much stronger than paper and have much more uniform strength throughout the x—y plane. They greatly enhance properties of laminates such as impact and tear strength. 

Carbon-Fiber Composites. Cured laminates of phenoHc resins and carbon-fiber reinforcement provide superior flammabiHty resistance and thermal resistance compared to unsaturated polyester and epoxy. Table 15 shows the dependence of flexural strength and modulus on phenoHc—carbon-fiber composites at 30—40% phenoHc resin (91). These composites also exhibit long-term elevated temperature stabiHty up to 230°C. 

Table 15. Strength Properties of Phenolic—Carbon-Fiber Composites...

Carbon, Carbides, and Nitrides. Carbon (graphite) is a good thermal and electrical conductor. It is not easily wetted by chemical action, which is an important consideration for corrosion resistance. As an important stmctural material at high temperature, pyrolytic graphite has shown a strength of 280 MPa (40,600 psi). It tends to oxidize at high temperatures, but can be used up to 2760°C for short periods in neutral or reducing conditions. The use of new composite materials made of carbon fibers is expected, especially in the field of aerospace stmcture. When heated under... 

Fig. 1. Specific strength and Young s modulus of various engineering materials where CF = carbon fiber HM/UHM = high modulus/ultrahigh modulus ...

Carbon fibers are generally typed by precursor such as PAN, pitch, or rayon and classified by tensile modulus and strength. Tensile modulus classes range from low (<240 GPa), to standard (240 GPa), intermediate (280—300 GPa), high (350—500 GPa), and ultrahigh (500—1000 GPa). Typical mechanical and physical properties of commercially available carbon fibers are presented in Table 1. 

The precursor fiber is subsequently washed and stretched to the low tex (denier) required for carbon fiber processing. Stretching also imparts considerable orientation to the polymer molecules and provides the basis for the highly oriented carbon stmcture that forms after carbonization. Special care is taken to avoid contamination or impurities that may form strength reducing flaws in the carbon fiber. 

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