Fiber Fracture Episode 2 pptx

FIBER FRACTURE: AN OVERVIEW t 21 Fig. 15. (a) The rough surface of a polycrystalline alumina fiber. SEM. (b) The grain structure of an alumina fiber. TEM. Rough surface of such brittle fibers makes them break at very low strain and it makes very difficult to handle them in practice. The room temperature fracture surface of a Nicalon fiber is shown in Fig. 16. Note the initiation of fracture at the fiber surface. The fracture surface shows a crack-initiating site and a planar minor region, a misty region, and finally a hackle region in which crack branching occurs. The initiating flaw may be an impurity, a surface nick due to handling, 22 K.K. Chawla Tuble 1. Effect of BN coating thickness on the mean strength of Nextel 480 fiber (Chawla et al., 1997) Coating thickness Weibull mean strength (wm) (GW 0 0.1 0.2 0.3 1 .0 1.63 2.00 2.47 1.82 I .27 or even a very minor chemical heterogeneity. Thus, it is very important to reduce the number and the size of defects during processing. Similar examples of fracture in E-glass fiber caused by a dust particle or a metallic inclusion in the near-surface region of the fiber, most likely formed during processing, can be found in the literature (Chandan et al., 1994). In order to meet the increasing demand for bandwidth, dense wavelength division multiplexing (DWDM) system designers must significantly increase the number of channels and decrease channel spacing. This has resulted in ever-stringent demands on the components that make up the telecommunications systems. For example, it is - Fig. 16. Fracture surface of a Nicalon fiber tested in tension at room temperature (courtesy of N. Chawla). Arrow indicates the site of initiation of fracture at the fiber surface. The fracture surface shows a planar mirror region, a misty region, and finally a hackle region in which crack branching occurs. The initiating flaw may be an impurity, a surface nick due to handling, or even a very minor chemical heterogeneity. FIBER FRACTURE: AN OVERVIEW 23 becoming necessary to write increasingly complex and precise fiber Bragg gratings (FBGs) on short fiber lengths. An FBG involves an optical fiber along whose core there occurs a periodic change in refractive index. Fiber Bragg gratings can be made during fiber drawing by a single laser shot or by using pulsed lasers after fiber drawing. In the single laser shot technique, fiber coating is applied after the grating is made. These FBGs are expected to reliably function for 20 to 40 years in a variety of conditions. Thus their mechanical reliability becomes an important issue. FBGs can be written by an argon-ion laser system operating in continuous wave (CW) mode at 244 nm or by KrF pulsed excimer laser operating at 248 nm. Varelas et al. (1997) studied the effects of laser intensity on the mechanical reliability of FBG. Their main results are summarized in Fig. 17, which shows the Weibull plots of pulse-irradiated fibers and continuous wave .+ pristine c- CW 0.5 kl/crn2 cw 1 W/crn2 .+ 0.5 W/cm2 -Q- I W/cm' I I I 3 5 Fracture strength (GPa) Fig. 17. Weibull plots of optical glass fibers subjected to pulse-irradiation and continuous wave treatments. The use of pulsed excimer radiation lowered the fiber fracture strength by as much as a factor of 4 compared to the fiber that was subjected to a CW argon-ion laser. The lower fracture strength of pulse-irradiated fiber is a result of the formation of microcracks in the material (after Varelas et al., 1997). 24 K.K. Chawla fibers. The use of pulsed excimer radiation for FBG production lowered the Weibull modulus as well as the fiber fracture strength by as much as a factor of 4 compared to the fiber that was subjected to a CW argon-ion laser for the FBG production. The lower fracture strength of pulse-irradiated fiber is a result of the formation of microcracks in the material. CONCLUSIONS Typically, fibers have a high surface area/volume ratio, which leads to fiber surface characteristics being very important in the fracture process. By far the major cause of fracture in fibers is the presence of flaws either on the surface of the fiber or in the interior. If the size of the flaw can be reduced through processing or safe handling, the strength of the fiber will increase. A stringent control of microstructural cleanliness and segregation are very important. This is true for all types of fibers: glass, carbon, metal, polymers, or ceramic, Fracture surface analysis of fibers can provide useful information. In particular, for noncrystalline fibers, the following fracture parameters can be obtained from an analysis of features on the fracture surface morphology: the mirror constant, an estimation of fracture toughness KI,, failure stress, flaw-to-mirror radius ratio, fracture surface energy, and the time to failure. REFERENCES Argon, AS. (1972) In: Treutise on Materials Science and Technology, p. 79, Academic Press, New York. Briant, C.L. (1989) Met. lkans., 20A: 243. Brownrigg, A., Boelen, A. and Toyama, M. (1 984) Adv. Fracr. Mech., 2: 350. Chandan, H.C., Parker, R.D. and Kalish, K. (1994) In: Fractogruphy of Glass, R.C. Bradt and R.E. Tressler Chawla, K.K. (1 998) Fibrvus Materiuls. Cambridge University Press, Cambridge, p. 206. Chawla, K.K., Xu, Z.R., Ha, J S., Schmucker, M. and Schneider, H. (1997) Appl. Compos. Marer:, 4: 263. Deurbergue, A. and Oberlin, A. (1991) Carbon, 29: 621. Gupta, P.K. (1994) In: Fractogruphy of Glass, p. 185, R.C. Bradt and R.E. Tressler (Eds.). Plenum Press, Horascek, 0. (1989) The Metallurgy of DopedlNon-Sug Tungsten. Elsevier, London, p. 251. Huttinger, K.J. (1990) Adv. Mutec, 2: 349. Jain, M.K. and Abhiraman, AS. (1987) J. Mater: Sci., 22: 278. Jenkins, S., Jacob, K.I. and Kumar, S. (2001) In: Heieruphusse Polymer Network Mureriuls: Synthesis, Characterimtion and Properties, p. 183, B.A. Rozenberg and G.M. Sigalov (Eds.). Gordon and Breach, New York. Johnson, D.J. (1987) In: Chemistry und Physics of Carbon, Vol. 20, p. 1, P.A. Thrower (Ed.). Marcel Dekker, New York. Johnson, D.J. (1990) In: Carbon Fibers and Filaments, p. 119, Kluwer, Boston, MA. Kozey, V.V. and Kumar, S. (1994) J. Marer: Res., 9: 2717. Kumar, S. (1989) SAMPE Q., 20 3. Mecholsky, J.J. (1994) In: Fractography of Glass, p. 37, R.C. Bradt and R.E. Tressler (Eds.). Plenum Press, Mecholsky, J.J., Freirnan, S.W. and Morey, S.M. (1977) Bull. Am. Cerum. Soc., 56 1016. (Eds.). Plenum Press, New York, NY, p. 143. New York, NY. New York. FIBER FRACTURE: AN OVERVIEW 25 Mecholsky, J.J., Freiman, S.W. and Morey, S.M. (1979) In: Fiber Optics: Advances in Research and Meyers, M.A. and Chawla, K.K. (1999) Mechanical Behavior of Materials. Prentice-Hall, Upper Saddle Northolt, M.G. (1981) J. Mare,: Sci., 16: 2025. Paris, H. (1996) In: Metallurn, Processing and Applications ofMetul Wires, p. 3, H.G. Paris and D.K. Kim Reynolds, W.N. (1981) Philos. Trans. R. Soc. London, A29: 451. Sawyer, L.C., Jamieson, M., Brikowski, D., Haider, M.I. and Chen, R.T. (1987) J. Am. Ceram. SOC., 70 Soraru, G.D., Mercadini, M. and Maschio, R.D. (1993) J. Am. Ceram. Soc., 76 2595. Sung, Y M. and Sung, I M. (1996) J. Mater: Sci., 31: 4775. Takahashi, T., Ochiai, I. and Satoh, H. (1992) Nippon Sreel Tech. Rep. 53, April, p. 102. Tanner, D., Dhingra, A.K. and Pigliacampi, J.J. (1986) J. Mer., 38: 21. Tarui, T., Takahashi, T., Tashiro, H. and Nishida, S. (1996) In: Metalhey, Processing and Applications of Taylor, S.T., Zhu, Y.T., Blumenthal, W.R., Stout, M.G., Butt, D.P. and Lowe, T.C. (1998) J. Mater: Sci 33: Varelas, D., Limberger, H.G. and Salathe, R.P. (1997) Electr: LRrt., 33: 704. Vukcevich, M.R. (1990) In: Pmc. 5th Inr. Tungsten Symp., p. 157, MPR Publishing, Bellstone. Wittenauer, J.P., Nieh, T.G. and Wadsworth, J. (1992) Adv. Muter: Process., September, 28. Yang, J M., Jeng, S.M. and Chang, S. (1996)J. Am. Cemm. Soc., 79: 1218. Development, p. 187, B. Bendow and S.S. Mitra (Eds.). Plenum Press, New York. River, NJ. (Eds.). TMS, Warrendale, PA. 798. Meral Wires, p. 87, H.G. Paris and D.K. Kim (Eds.). TMS, Warrendale, PA. 1465. [...]... BP/A -26 2 Curtin, W.A (1999) Stochastic damage evolution and failure in fiber- reinforced composites Adv Appl Mech., 3 6 163 -25 3 Doege, E., Kroff, A and Rotarescu, M.I (20 00) FEM analysis of wire drawing regarding the material damage In: Pmceedings TPR, Cluj-Napoca, pp 131- 136 Elices, M (1985) Fracture of steels for reinforcing and prestressing concrete In: Fracture Mechanics of Concrete, pp 22 6 -27 1,... structural mechanics of fibers J Polym Sci., Pur? C, 2 0 21 5 -25 1 Hearle, J.W.S (20 00) A critical review of the structural mechanics of wool and hair fibres Int J Biol Macromol., 27 : 123 - 128 Hearle, J.W.S and Sparrow, J.T (1979) Mechanics of the extension of cotton fibers, 11 Theoretical modeling J Appl Polym Sci., 24 : 1857-1874 Johnson, R.A and Wilson, W.D (19 72) In: Interatomic Potentials and Simulation o... terephthalamide) fibers J Polym Sci Pdym Phys Ed., 21 : 1757-1783 Nam, W.J and Bae, C.M (1995) Void initiation and microstructural changes during wire drawing of pearlitic steels Muter: Sci Eng., 20 3: 27 8 -28 5 Niray-Szab6,I and Ladik, J (1960) Strength of silica glass Nature, 188: 22 6 -22 7 Northolt, M.G and van der Hout, R (1 985) Elastic extension of an oriented crystalline fibrc Polymer, 26 : 3 10-3 16... shock wave 25 55 32 36 41 7 I 7 1.7 17 @Pa) (100) References Kelly and Macmillan (1986) Esposito et al (1980) Esposito et al (1980) Esposito et al (1980) Johnson and Wilson (19 72) Milstein and Farber (1980) Brenner (1956) Kobayashi and Hiki (1973) McQueen and Marsh (19 62) (1981) are: 10.4 GPa in (1lo), 12. 6 GPa in ( 111) and 15 .2 GPa in (100) Tensile strengths at 10.9, 22 .3 and 15.3 GPa for A 120 3 whiskers... Rossell6, C (20 02b) Assessment of defect size in brittle fibers En# Fruct Mech., 69: 1057-1066 Gurson, A.L (1977) Continuum theory of ductile rupture by void nucleation and growth, Part 1 Yield criteria and flow rules for porous ductile media J Eng Mater: Technol., 99: 2- 15 He, T (1986) An estimate of the strength of polymers Polymer, 27 : 25 3 -25 5 Hearle, J.W.S (1967) The structural mechanics of fibers J... and Llorca, J (20 00) Mechanical properties of Sigma 1140+ Sic fibres prior and after composite processing Adv Comp Lett., 9: 29 5-3 02 Grimsditch, M.H., Anastassakis, E and Cardona, M (1978) Effect of uniaxial stress on the zone-center optical phonon of diamond Phys Rev B, 18 (2) : 901-90.1 Guinea, G.V., Rojo, F.J and Elices, M (20 02a) Stress intensity factors for internal circular cracks in fibers under... (1995) Fracture Mechanics CRC Press, Boca Raton, F L Argon, AS., Im, J and Safoglu, R (1975) Cavity formation from inclusions in ductile fracture Metall Trans., 6 A 825 -837 Bacon, R (1960) Growth, structure, and properties of graphite whiskers J Appl Phys., 31 (2) : 28 3 -29 0 Baltussen, J.J.M and Northolt, M.G (1996) A model for the tensile curve with yield of a polymer fibre Polym Bull., 3 6 125 -131 Beremin,... length decreases Carbon fibres are considered in detail in the paper by Lavin in this volume MODELS OF FIBRE FRACTURE 35 7 8 a HERCULES AS4 TORAYCAT30 m 9 6 I 0 + 2 W u 1 4- E L [) F I TORAYCAM4 W 1 (Gauge length 25 .4 mm) 3- 0- W 2 v) i 25 + ob Y W 2- W + I I I I DIAMETER ( e I 1 , l l L p mm) 1- d 0 2 4 6 8 I 10 GAUGE LENGTH (mm) Fig 4 Tensile strength of carbon fibre as a function of diameter (Fitzer... theoretical tensile strength of copper Philos Mag A, 41 (2) : 25 1 -25 9 Faucon, A., Lorriot, T., Martin, E., Auvray, S., Lepetitcorps, Y , Dyos, K.and Shatwell, R.A (20 01) Fracture behaviour of model silicon carbide filaments Camp Sci Technol., 61(3): 347-354 Feughelman, M (1994) A model for the mechanical properties of the a-keratin cortex Text Res J., 64(4): 23 6 -23 9 Fitzer, E and Frohs, W (1990) Modem carbon... E (1949) Rep Prog Phys., 12: 185 Panar, M., Avakian, P., Blume, R.C., Gardner, K.H., Gierke, T.D and Yang, H.H (1983) Morphology of poly@-Phenylene Terephthalamide)fibers J Polym Sci Polym Phys Ed., 21 : 1955-1969 Perepelkin, K.E (1 9 72) Comparative estimate of the theoretical, highest attainable strength and rigidity of oriented layer structures Sov Muter: Sci., 8 (2) : 198 -20 2 Peterlin, A (1981) Tensile . 1465.