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i it. Appendix C FIBER-QUALITY PARAMETERS OF SELECTED ASBESTOS, WHISKER, AND GLASS FIBERS The strength-diameter effect of fine wires and fibers has been discovered and rediscovered several times during the lent 250 years. Each t ime it excited great interest within the sc lent if ic community but was soon doubted and finally ignored after a few years. It is difficult to explain the reasons for this cyclical interest in the strength-diameter effect. One reason could be that no satisfactory theory has been developed and experimentally proven. Today, it is possible to observe surface defects and other submicroscopic features, such as the dissolution pattern of fibers, but the surface structure of fine fibrous substances still cannot be determined. In the early 1800s, Karmarsch (1834) completed an extensive and systematic study on the strength-tiameter effect of 18 different metal and alloy wires. In 1859, he derived an equation expressing the relationship between the increasing strength (F.) and the decreasing diameter (D) of small-diameter wires. His equation (rephrased by Griffith, 1921) is: F = A + B/D, where A and B are constants. (C-1) The constant A in the Karmarsch equation (C-1) was interpreted by Orowan ( 1933) 88 the strength of the internal structure and B as the strength of the surface structure. However, the Karmarsch equation did not satisfy all the more than 100 available strength-diameter measurements. This problem was recently resolved (Zoltai, 1981) by changing the surface area-to-volume ratio (BID in the Karmarsch equation) to incorporate other features of the surface structure, e.g., the depth of the surface layer, the presence of growth steps (Marsh, 1962), and the effect of longitudinal cleavages (Cook ant Gordon, 1964~. Thus, of ~ hi (1 + 4R/D)1 + 4k/D (C-2) where of is the strength of the fiber, Al is its internal strength, and R and k are factors expressing the increased strength of the surface layer over that of the internal structure. 253

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254 Table C-1 shows the fiber characterist iC8 (internal strength, K and k constants, etc.) of a selected group of natural and synthetic fibers. The values shown in the table illustrate the general characteristics of the examples and the relative magnitudes of the parameters given. Experimental data in reports by various researchers are difficult to compare because they often use different expressions of strength, different methods, and different unite of measurement. Further limitations result from inaccurate readings of strength and diameter values from published small-scale graphs. SIGNIFICANCE OF THE FIBER-QUALITY PARAMETERS From the measurement of the tensile strength of sets of fibers and from subsequent calculations (using the above equations), one can calculate: (1) the internal strength of the fibers (of) and (2) two constants (K and k), which express the relative increase in the strength of the surface structure.- There parameters reflect the differences in the mechanical properties of fibers that grew under different conditions or that were modified by treatment and wear. The following conclusions about fiber-quality parameters may be relevant to the potential health effects of fibers: ( 1) The mechanical properties of fibers are directly related to the common properties of asbestifonm fibers. Consequently, the three parameters can be used an numerical indicators of the degree of asbestifo`= development of fibers. (2) - The two constants, K and k, must be positive for asbestiform fibers in order to account for their enhanced strength and flexibility. - The K and k constants must be equal to zero for crystals that have no enhanced strength despite a defect-free surface structure. - The R and k constants must be negative for cleavage fragments and other fragments whose surfaces are weaker than their internal structure because of the physical damage introduced by fracturing and subsequent processes. (3) Because of the interdependent nature of the common asbestiform fiber properties, these three parameters may include a direct or indirect measure of the critical physicochemical property or properties that may be primarily responsible for the adverse health effects of asbestifonm fibers. However, the nature of relationship between the fiber quality and carcinogenic potential of asbestiform fiber" is still unknown.

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259 REFERENCES A~deregg, F. 0. 1939. Strength of gia88 fiber. Ind. Eng. ~em. 31: 290-298. Bartenev, G. M., and L. R. Izmailova. 1962. Defect-free glass fibers. (In Russian) Akad. Nauk. SSSR, Chem. Tech. Sect. 146:196-198. Bateson, S. 1958. Critical study of the optical properties of glass fibres. J. Appl. Phys. 29 :13-21. Bayer, P. D., and R. E. Cooper. 1967. Size-atrength effects in sapphire and silicon nitride whiskers at 20C. J. Mater. Sci. 2:233-237. Bokshtein, S. Z., S. T. Koshlcin, and I. L. S~otkov. 1963. Tensile testing of filament crystals of copper, nickel and cobalt to failure. Sov. Phys. Solid State 4:1271-1277. Bokshtein, S. Z., S. T. Koshkin, M. P. Nazarrova, and I. I. Svetlov. 1968. Size effect and anisotropy in the strength of sapphire whiskers at room temperature. Sov. Phys. Solid State 9:1488-1494. Brenner, S. S. 1956. Tensile strength of wElakera. J. Appl. Phys. 27:1481-1491. Brenner, S. S. 1958. Growth and properties of whiskera. Science 128: 569-575. Cook, J. 1970. llechanical testing of whiskers. Composites (March):176- 180. Cook, J., and J. J. Gordon. 1964. A mechanism for the control of crack propagation in all brittle systems. Proc. R. Soc. London, Ser. A 282: 508-518. E`rans, C. C., J. E. Gordon, and D. M. Marsh. 1964. The strer~gth of whiskers of silicon, zinc oxide and phthalocyas~ine. Proc. R. Soc. London, Ser. A 282: 218-220. Ewald, W., and M. Polanyi. 1925. Plastizit~t und Festigkeit von Steinsalz unter Wasser. Z. Phys. 31:29-50. Fridman, V. Y., and A. A. Shpunt. 1963. Investigation of the strength of lithium fluoride crystal fragments. Sov. Phys. Solid State 5:575-579. Griffith, A. R. 1921. The phenomena of rupture and flow in solida. Phil. Trans. R. Soc. London, Ser. A 221:163-198. Gyulai, Z. 1954. Festigkeit- und Plastizit~teigenschaften ~ron NaC1 Nadelkristallen. Z. Phys. 138:317-321. Gyulai, Z., E. Hartman, and B. Je~zenazky. 1961. Zerreissfestigkeit- Messungen an NaC1 Nadelkrist~ len (whiskera). Phys. Satue Solidi 1:726-729. Herzog, J. A. 1963. Strength investigations with unidimensionally grown cyrstalline iron (whisker). Metallurgia 17:7-14. Herzog, J. A. 1967. Entwicklung und Zukunit in der Whiskerforachu~g. Jahrb. Wissen. Gesellach. Luftfahrt. (WGLR) 30nes, B. F. 1971. Further observations concer~ing the effect of diameter on the fracture strength and Yung's Modulus of carbon and graphite fibers made from polyacrylonitrile. J. Mater. Sci. 6:1225-1227. Jones, B. F., and R. G. Duncan. 1971. The effect of fiber diameter on the mechanica' properties of graphite fibers maDufacturet from polyacrylonitrile and rayon. J. Mater. Sci. 6:289-293. -

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260 Kar~arsch, R. 1834. Versuche Uber die Festigkeit der zu Draht gazogenen Metallen. Jhhrb. Polytech. Inst. Wien 18:57-115. Xarmarach, K. IB59. Uber die absolute Festigkeit der MetalldrKhte. Mitt. Gew. Ver. Konigr. Hanover, pp. 137-156. Kelsey, R. H., and R. H. Krock. 1967. Tension testing alumina whiskers. J. Mater. Sci. 2:146-1 59. Kirchner, H. P., and P. Knoll. 1963. Silicon carbide whiskers. J. he. Ceram. Soc . 46: 299-300. Melees, M. N., A. P. Krusilina, and V. N. Rosanckl]. 1972. Ultimate strength of naturally fibrous rutile, antimony and jamesonite crystals. (In Russian) C. R. Acad. Bulg. Sci. 25:1085-1088. Marsh, D. M. 1963. Stress concentration at steps on crystal surfaces and their role in fracture. Fracture of Solids, Metal. Society Conference 20. ~teracience Publishers, New York. Mehan, R. L., E. Feingold, and E. Gatti. 1965. Technical Report AFFIL- TR 65 275, August. Mehan, R. L., W. H. Sutton, and J. A. Herzog. 1966. A review of measuring the strength of whiskers and their role in reinforcing ductile matrices. AIAA J. 4:1889-~898. NadgorDyi, E. M., L. F. Grigore~ra, and A. P. Ivanor. 1965. The mechanical properties of synthetic fibrous fluoramphiboles and certain forms of natural asbestos. Izv. Akad. Nauk. SSSR Neorg. Mater. ~ :1117-1123. Noone, M. J. 1967. The preparation, structure and mechanical properties of filamentary forms of silicon carbide. Ph.D. Thesis. University of Leeds, United Kingdom. Orowan, E. 1933. Die erhohte Festigkeit dinner F8den, der Joffe-Effekt und verwandLe Eracheinungen vom Standpunkt der Griffitachen- Bruchtheorie. Z. Phys. 86:195-213. Perry, A. J., K. Phillips, and E. de Lamotte. 1971. The mechanical properties of carbon fibres. Fibre Sci. Technol. 3:317-319. Reinkober, O. 1931. Die Zerreissfestigkeit dinner Quarzfdden. Phys. Zeitachr. 32:243-250. Salkind, M. J., F. D. Lemkey, and F. D. George. 1970. Whisker composites by eutectic solidification. Chapter 10 in A. P. Levitt, ed. Whisker Technology. Interacience Publishers, New York. Soltis, P. J. 1967. A new method and technique for tension testing whiskers. J. Mater. Sci. 2:300-324. Webb, W. W., R. D. Dragadorff, and W. D. Forgeng. 1957. Dislocations of whiskers. Phys. Rev. 108:498-499. Webb, W. W., H. D. Bathand, and R. S. Shaffer. 1966. Strength characteristics of whisker crystals, microcrystals and macrocrystAla. Chapter 14 in J. J. Purke, N. L. Reed, asks V. Weiss, eds. Strengthening Mechanisms. Syracuse University Press, Syracuse, N.Y. Weik, H. 1959. Whisker structure and tensile strength. J. Appl. Phys. 30:791-792. Wolff, E. G., and T. D. Coakren. 1965. Growth and morphology of magnesium oxide whiskers. J. Am. Ceram. Soc. 48:279-285. Zoltai, T. 1981. Amphibole asbestos mineralogy. Pp. 23?-278 in D. R. Veblen, ed. Amphiboles and Other Hydrous Pyriboles. MSA Reviews in Mineralogy, 9A. Mineralogical Society of America, Washlugton, D.C.