Page images

6. Thome, D. J.: Manufacture of Carbon Fibre From PAN. Strong Fibres, W. Watt and B. V. Perov. eds., Elsevier Science Publ. Co., Inc., 1985, pp. 475^94.

7. Riggs, Dennis M.; Shuford, Richard J.; and Lewis. Robert W.: Graphite Fibers and Composites. Handbook of Composites, George Lubin, ed., Van Nostrand Reinhold Co., c.1982, pp. 196-271.

8. Fitzer, E.: Carbon Fibers: Present State and Future Expectations. Carbon Fibers, Filaments and Composites, J. Figueiredo. C. A. Bernardo, R. T. K. Baker, and K. J. Huttenger, eds., Kluwer Academic Publ., 1990, pp. 3-41.

9. Bacon, Roger: Carbon Fibers From Rayon Precursors. Chemistry and Physics of CarbonA Series of Advances, vol. 9. P. L. Walker, Jr., and Peter A. Thrower, eds., Marcel Dekker, Inc., 1973, pp. 1-102.

10. Singer, Leonard Sidney: High Modulus, High Strength Carbon Fibers Produced From Mesophase Pitch. U.S. Patent 4,005,183. Jan. 1977.

11. Singer, L. S.: and Lewis, I. C.: ESR Study of the Kinetics of Carbonization. Carbon, vol. 16, no. 6, 1978, pp. 417-423.

12. Diefendorf, Russell J.; and Riggs, Dennis M.: Forming Optically Anisotropic Pitches. U.S. Patent 4,208,267, June 1980.

13. Fitzer, E.; Kompalik, D.; and Mayer, B.: Influence of Additives on Pyrolysis of Mesophase Pitch. Carbon '86Proceedings of the International Conference on Carbon, Deutschen Keramishchen Gesellschaft, Bad Honnef (Baden-Baden, Federal Republic of Germany), 1986, p. 842.

14. Nazem, F. F.: Flow of Molten Mesophase Pitch. Carbon, vol. 20, no. 4, 1982, pp. 345-354.

15. Edie, D. D.; and Dunham, M. G.: Melt Spinning Pitch-Based Carbon Fibers. Carbon, vol. 27, no. 5, 1989. pp. 647-655.

16. Edie, D. D.: Pitch and Mesophase Fibers. Carbon Fibers. Filaments and Composites, J. Figueiredo, C. A. Bernardo, R. T. K. Baker, and K. J. Huttenger, eds., Kluwer Academic Publ., 1990, pp. 647-655.

17. Mochida, Isao; Toshima, Hiroshi; Korai, Yozo; and Naito, Tsutomu: Modification of Mesophase Pitch by Blending. Part 2—Modification of Mesophase Pitch Fibre Precursor With Thermoresisting Polyphenyleneoxide (PPO). J. Mater. Sci., vol. 23, no. 2, Feb. 1988, pp. 678-686.

18. Hughes, T. V.; and Chambers, C. R.: Manufacture of Carbon Filaments. U.S. Patent 405,480,1889.

19. Tibbetts, G. G.: Vapor-Grown Carbon Fibers. Carbon Fibers, Filaments and Composites, J. Figueiredo, C. A. Bernardo, R. T. K. Baker, and K. J. Hiittenger, eds., Kluwer Academic Publ., 1990, pp. 79-94.

20. Baker, R. T. K.: Electron Microscope Studies of Catalytic Growth of Carbon Fibers. Carbon Fibers, Filaments and Composites, J. Figueiredo, C. A. Bernardo, R. T. K. Baker, and K. J. Hiittenger, eds., Kluwer Academic Publ., 1990, pp. 405^39.

21. Endo, M.; and Komaki. K.: Formation of Vapor-Grown Carbon Fibers by Seeding Method of Metal Ultra-Fine Particles. Extended Abstracts of 16th Biennial Conference on Carbon, American Carbon Society, San Diego, CA, p. 523, 1983.

22. Koyama, T.; and Endo, M. T.: Method for Manufacturing Carbon Fibers by a Vapor Phase Process. Japanese Patent 1982-58,966, 1983.

Chapter 3

Effect of Microstructure and Shape on
Carbon Fiber Properties

D. D. Edie and E. G. Stoner

Clemson University

Clemson, South Carolina

Introduction 42

Carbon Fiber Processes 43

Effect of Graphite Structure on Fiber Properties 44

Brittle Failure Mechanism 45

Microstructure of Carbon Fibers 47

Microstructure of PAN-Based Carbon Fibers 47 Microstructure of Pitch-Based Carbon Fibers 48 Effect of Microstructure on Fiber Properties 53

Effect of Microstructure on Tensile Properties of Carbon Fibers 54 PAN-Based Carbon Fibers 54 Pitch-Based Carbon Fibers 55 Effect of Microstructure on Compressive Properties of Carbon Fibers 57 PAN-Based Carbon Fibers 59 Pitch-Based Carbon Fibers 59 Effect of Fiber Shape on Fiber and Composite Properties 61 Effect of Shape on Tensile Strength of Carbon Fibers 61 PAN-Based Carbon Fibers 61 Pitch-Based Carbon Fibers 61 Effect of Shape on Compressive Strength for Carbon Fibers 62 PAN-Based Carbon Fibers 64 Pitch-Based Carbon Fibers 66 Summary 66 Acknowledgments 66 References 67


In carbon-carbon (CC) composites, carbon fibers reinforce the brittle carbon matrix material. Because these reinforcing fibers determine, to a large extent, the strength and stiffness of this composite material, optimizing the properties of CC composites requires a thorough understanding of both the properties and peculiarities of carbon fibers.

As in other classes of fiber-reinforced composite materials, the required fiber properties depend on the particular composite application. In certain propulsion applications of CC composites, high fiber strength is critical and stiffness is less important. In these applications, polyacrylonitrile (PAN) based carbon reinforcing fibers are the logical choice. In other structural applications, the CC composite experiences both tensile and compressive loading. This loading makes fiber compression properties critical, and, again, PAN-based fibers are preferred. In applications in which interlaminar strengthening is necessary, fiber strength and stiffness are not as critical as the ability to weave a complex fabric preform from the carbon reinforcing fibers. Here the low modulus of rayon-based carbon fiber, combined with its medium strength, results in the moderate strain to failure necessary for processing on weaving equipment. However, in large space structures, low thermal expansion or extremely high stiffness may be critical. Pitchbased carbon fibers are uniquely suited for these applications. Finally, the strength of the bond between the fiber and the matrix also can be critical to composite performance. A strong interfacial bond may make the composite more resistant to interlaminar shear. On the other hand, because the carbon matrix material is brittle, a weak interfacial bond can, as in ceramic composites, serve as a toughening mechanism. Thus, in CC composites, fiber-matrix bonding often is a compromise between toughening the composite and improving its interlaminar properties.

To meet these different requirements, three types of carbon fibers presently are used in CC composites: these are rayon-based, PAN-based, and pitch-based fibers. Each has its own particular strengths and weaknesses. To better understand both the limitations and the potential of these different carbon fibers, this chapter briefly reviews the processes used to produce them and the ultimate properties that they can attain. The mechanism of brittle fracture then is discussed to better understand the practical limits for carbon fiber properties. Finally, the effect that processing has on the carbon fiber structure and the relationship between this structure and the physical properties of the fiber will be explained. This explanation will show the potential for future increases in physical properties for each type of carbon fiber.

Rayon-based fibers were the first carbon fibers used in CC composites. However, because of their higher strength and stiffness, PAN-based and pitch-based carbon fibers are used to reinforce the vast majority of current CC structures. This chapter will concentrate on PAN-based and pitch-based carbon fibers, the

« PreviousContinue »