Strength of carbon fibers

Fig. 5.18. Comparison of shear strengths of carbon fiber-epoxy matrix composites determined from three dificrcnt test methods. Fiber surface conditions as in Fig. 5.17. After Drzal and Madhukar (1993).

Fig. 6.24. Comparison of notched strength of carbon fiber-epoxy matrix quasi-isotropic [0°/ 45°/90°...

The present article is centered around macromolecular and supramolecular structures obtained upon use of benzene as a regular building block. While, e.g., the gas permeability of polyethylene tereph-thalate)s,35 the mechanical strength of carbon fibers,36 and the ion conductivity of polybenzimidazoles24 are important features from a practical viewpoint, the focus here is on the occurrence of -conjugation, or lack thereof, originating from the repetition of the aromatic benzene units in various structural motifs. If the reader regards materials... 

Following Huttinger (1990), we can correlate the modulus and strength of carbon fiber to its diameter. We make use of Weibull statistics to describe the mechanical properties of brittle materials (see Chapter 10). Brittle materials show a size effect, i.e. the experimental strength decreases with increasing sample size. This is demonstrated in Fig.8.10 which shows a log-log plot of Young s modulus as a function of carbon fiber diameter for three different commercially available carbon fibers. The curves in Fig. 8.10 are based on the following expression ... 

Use the web to research the elastic modulus and yield strength of carbon fiber composites. How do these materials compare to aluminum, steel, and titanium ... 

Temperature is one of the processing parameters which has a pronounced effect on the failure strength of carbon fibers. This effect is quite different for MP based and PAN based fibers. As the heat treatment temperature (HTT) is raised, the strength of a mesopitch based fiber, tested at room temperature, progressively increases [3] [38] [54-55]. Conversely, that of most PAN based fibers undergo a maximum at about 1300-1500 C (Figure 12). 

A.3.2 Factors affecting tensile strength of carbon fibers... 

Figure 3.20 Strengths of carbonized fibers after etching in air at 450°C. Source Reprinted with permission from Johnson JW, Applied Polymer Symposia, No. 9, 229-243, 1969. Roiis Royce.

Figure 5.7 Tensile strength of carbon fiber monofilaments as function of fiber diameter. Source Reprinted with permission from Fitzer E, PAN-based carbon fibers-present state and trend of the technology from the viewpoint of possibilities and limits to influence and control the fiber properties by the process parameters, Carbon, 27(5), 621-645, 1989. Copyright 1999, Elsevier.

Table 5.11 The effect of gage length on the tensile strength of carbon fibers heat treated to 2500°C.

Figure 5.43 The tensile strength of carbon fibers as a function of the density of stabilized fibers from an AN/ MA precursor at stabilization temperatures of O 240°C A 255°C 270°C. Source Reprinted with permission from Takaku A, Hashimoto T, Miyoshi T, J AppI Polym Sci, 30, 1565, 1985. Copyright 1985, John Wiley Sons Ltd.

Figure 15.5 Ultimate tensile strength of carbon fiber reinforced cement. Source Reprinted from Aveston J, Mercer RA, Sillwood JM, Conference Proceedings Composites Standards Testing and Design, NPL 1974, IPC Science Technology Press, 93-103, 1974.

Bouix et al describe the interface tailoring of carbon fibers [14], whilst Lawcock et al [15] considered the effects of the fiber/matrix adhesion on the strength of carbon fiber reinforced metal laminates and the effects of the fiber/matrix adhesion on the impact strength of carbon fiber reinforced metal laminates [16]. 

Figure 16.4 Flexural strength of carbon fiber reinforced Al for interface carbides from 0-10% showing different faiiure mechanisms as determined by f ractography. Source Reprinted with permission from Lacom W, Degischer HP, Schuiz P, Assessment and control of surface reactions of carbon fibres in light weight metai matrix composites, Key Eng Mater, 127(1,2), 679-686, 1997. Copyright 1997, Trans Tech Pubiications.

Manders PW, Kowalski IM, The effect of small angular fibre misalignments and tabbing techniques on the tensile strength of carbon fiber composites, 32nd International SAMPE Symposium, 985-996, Apr 6, 1987. 

Harding J, Dong L, Effect of strain rate on the interlaminar shear-strength of carbon-fiber-reinforced laminates, Composite Science Technology 51(3), 347-358, 1994. 

Ohsawa T, Miwa M, Kawade M, Tsushima E, Axial compressive strength of carbon fiber, J Appl... 

Prandy JM, Hahn HT, Compressive strength of carbon fibers, SAMPE Quarterly, Society for the Advancement of Materials and Process Engineering, 22(2), 47-52, 1991. 

Soutis C, Measurement of the static compressive strength of carbon-fiber epoxy laminates, Composite Sci Technol, 42(4), 373-392, 1991. 

Several methods have been used to determine the compression strength of carbon fiber and its composites—The Loop Test [90] Single Filament in a Beam [91] Critical Length under Compression [92] Micro-compression [93,94] Fiber Recoil [95-97] Piezo Method [98,99] Raman Spectroscopy [100-102] Composite [103,104] and Mini-composite [105]. 

Figure 20.16 Effect of V, on longitudinal compressive strength of carbon fiber epoxy resin iaminate at 20°C.

The SEM observations revealed that PAN based fibers failed by a buckling mechanism, whereas MP based fibers failed by shear. The TIOOO fiber exhibited the highest compressive failure strength and tensile strain to break. Compressive strengths of carbon fibers are related to the ability to absorb energy, as shown in Figures 20.20 and 20.21. 

Figure 20.26 Variation of longitudinal compressive strength of carbon fiber epoxy resin laminate with temperature showing transition from shear mode to buckling mode failure. Failure depends on the shear modulus of the matrix and shear strength of the fibers and a similar effect is observed with the uptake of water. Source Reprinted with permission from Ewins PD, Potter RT, Phil Trans R Soc London, A294, 507-517, 1980. Copyright 1980, The Royal Society of Chemistry.

Note The disposition of boundaries between the fiber types is somewhat arbitrary. The tensUe strength of CARBON FIBERS is, however, flaw controlled and therefore, the measured values increase strongly as the diameter of the filaments is decreased. 

The tensile modulus E and strength of carbon fibers are shown as a function of carbonization temperature in Figure 8 [21]. The carbon fiber modulus increases with increasing carbonization temperature. This increase in modulus is caused by increased graphitization of the carbon at higher temperatures, since the more perfect graphite has a higher modulus than the less ordered carbon sheets. 

The tensile breaking strength of carbon fibers is dominated by flaws within the fiber and on its surface. Some of the flaws that can affect the fiber strength include ... 

Surface treatment has been observed to change the breaking strength of carbon fibers. Bahl et al. [40] and Fitzer and Weiss [41] have observed that treatment of carbon fibers in nitric acid initially increases the fiber tensile strength. Continued anodization results in a loss in strength caused by fiber damage. This initial increase in strength can be explained by removal from the fiber surface of defects, which can initiate fracture. 

Hutchinson JW, Phillips DC (1979) The dependence of strength of carbon fibers on length. Fiber Sci Technol 12 217-233... 

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