JOURNAL OF MATERIALS PROCESSING TECHNOLOGY 209(2009)572-576 575 extensive pullout as shown in Fig 5b. This was according to the nonlinear tensile stress-strain curves as shown in Fig 3 SiC matrix Conclusions PyC interpet Tensile stress-strain curves exhibited a nonlinear behavior and can be divided into three regions: a very small ini tial linear region followed by a large nonlinear region and finally a quasi-linear region. The tested specimens mainly fractured at the crossover of needling fibers and unidirec tional fibers. And fracture surfaces were very ragged, with the fibers showing multi-step fracture and extensive pullout. The multi-step fracture of fibers and nonlinear stress-strain curves indicated a typical non-brittle behavior of the multi- Fig 6- Pyc interphase and interfacial debonding. ply needled C/Sic composite due to the multi-type damage patterms when specimens subjected to the increasing tensile stress Damage pattems included matrix cracks propagating, interfacial debonding/slidding, and fibers bridging and break- alignment of unidirectional carbon fibers was disturbed by ing Needling process caused a crimp around needling fibers needling fibers, resulting in a crimp around needling fibers. and reduced the fraction of bearing fibers in plane. All these As shown in Fig. 4b, the direction of needling fibers was needling-induced damages were the main reasons for the fail changed to through-thickness direction from in-plane direc- ure of the multiply needled C/SiC composite tion, so the uniformity of the ideal unidirectional plies was disturbed, lessening the amount of bearing-fibers in-plane at the needling locations. All damages mentioned above were Acknowledgements referred to "needling-induced damage". When specimens yere subjected to tension, the tensile loads were primarily The authors acknowledge the financial support of the Natu carried by fibers around the needling positions, so the stress ral Science Foundation of China( Contract no. 50672076, no concentrated within fiber clusters around the needling posi- 90405015)and the National Young Elitists Foundation(Con- tions Such stress concentrations can trigger localized damage tract no. 50425208) within fiber clusters. This can explain well why the fracture of the carbon fber clusters mainly occurred in needling areas. REFERENCES The composite properties were greatly influenced by the interfacial properties. The interphase of the tested specimens is shown in Fig. 6. The layered PyC interphase was introduced Boitier, G, Viens, J, Chermant, J L, 1997. Tensile creep results on into composites to weaken the bonding strength between Cr-SiC composite. Scripta Mater. 37(12), 1923-1929 carbon fibers and Sic matrix, so the interfacial debonding Bouquet, C, Fischer,R, Larrieu, J.M., Uhrig, G, Thebault,J, 2003 occurred when specimens subjected to tensile loads, as shown Composite technologies development status for scramjet in Fig. 6. Thus microcracks can be arrested and deflected by the pplications. In: 12th AIAA International Space Planes and PyC interphase, as shown in Fig. 7. As a result, the multiply ypersonic Systems and Technologies, Norfolk, America, December 15-19 needled C/Sic composite exhibited non-brittle fracture char- amus, G, Guillaumat, L, Baste, S, 1996. Development of acteristics, with the fibers showing multi-step fracture and damage in a 2D woven C/Sic composite under mechanical I. M 56,1363-1372 Cao. H C. Bischoff. E. Sbaizero. o. Ruhle. M.. Evans. A.G. Marshall, D B, Brennan, JJ., 1990. Effect of interfaces on the properties of fiber-reinforced ceramics. J Am Ceram Soc. 73 1691-1699 Chiang, Y.M., Haggerty, J.S., Messner, R.P., Demetry, C, 1989 Reaction-based processing methods for ceramic-matrix opposites. Am. Ceram Soc. Bull. 68(2) Christin, E, 2002. Design, fabriction, and application of nermostructural composites (rsC)like C/C, C/SiC, and Sic/Sic composites. Adv. Eng Mater. 4(12),903-912. Krenkel, W, Berndt, E, 2005. C/C-SiC composites for space applications and advanced friction systems. Mater. Sci. Eng. A 412,177-181 Lacoste. m. A. Joyez, P, 2002. Carbon/carbon xtendib Acta Astronaut. 50(6), 357-3 Lomov. s.v. B, Bischoff, T, Ghosh, S.B., Truong Chi, T. Fig 7- Deflection of microcracks and fracture of fibers. Verpoest, I, 2002. Carbon composites based on multiaxialjournal of materials processing technology 209 (2009) 572–576 575 Fig. 6 – PyC interphase and interfacial debonding. alignment of unidirectional carbon fibers was disturbed by needling fibers, resulting in a crimp around needling fibers. As shown in Fig. 4b, the direction of needling fibers was changed to through-thickness direction from in-plane direc￾tion, so the uniformity of the ideal unidirectional plies was disturbed, lessening the amount of bearing-fibers in-plane at the needling locations. All damages mentioned above were referred to “needling-induced damage”. When specimens were subjected to tension, the tensile loads were primarily carried by fibers around the needling positions, so the stress concentrated within fiber clusters around the needling posi￾tions. Such stress concentrations can trigger localized damage within fiber clusters. This can explain well why the fracture of the carbon fiber clusters mainly occurred in needling areas. The composite properties were greatly influenced by the interfacial properties. The interphase of the tested specimens is shown in Fig. 6. The layered PyC interphase was introduced into composites to weaken the bonding strength between carbon fibers and SiC matrix, so the interfacial debonding occurred when specimens subjected to tensile loads, as shown in Fig. 6. Thus microcracks can be arrested and deflected by the PyC interphase, as shown in Fig. 7. As a result, the multiply needled C/SiC composite exhibited non-brittle fracture char￾acteristics, with the fibers showing multi-step fracture and Fig. 7 – Deflection of microcracks and fracture of fibers. extensive pullout as shown in Fig. 5b. This was according to the nonlinear tensile stress–strain curves as shown in Fig. 3. 4. Conclusions Tensile stress–strain curves exhibited a nonlinear behavior and can be divided into three regions: a very small ini￾tial linear region followed by a large nonlinear region and finally a quasi-linear region. The tested specimens mainly fractured at the crossover of needling fibers and unidirec￾tional fibers. And fracture surfaces were very ragged, with the fibers showing multi-step fracture and extensive pullout. The multi-step fracture of fibers and nonlinear stress–strain curves indicated a typical non-brittle behavior of the multi￾ply needled C/SiC composite due to the multi-type damage patterns when specimens subjected to the increasing tensile stress. Damage patterns included matrix cracks propagating, interfacial debonding/slidding, and fibers bridging and break￾ing. Needling process caused a crimp around needling fibers and reduced the fraction of bearing fibers in plane. All these needling-induced damages were the main reasons for the fail￾ure of the multiply needled C/SiC composite. Acknowledgements The authors acknowledge the financial support of the Natu￾ral Science Foundation of China (Contract no. 50672076, no. 90405015) and the National Young Elitists Foundation (Con￾tract no. 50425208). references Boitier, G., Viens, J., Chermant, J.L., 1997. Tensile creep results on a Cf-SiC composite. Scripta Mater. 37 (12), 1923–1929. Bouquet, C., Fischer, R., Larrieu, J.M., Uhrig, G., Thebault, J., 2003. Composite technologies development status for scramjet applications. In: 12th AIAA International Space Planes and Hypersonic Systems and Technologies, Norfolk, America, December 15–19. Camus, G., Guillaumat, L., Baste, S., 1996. Development of damage in a 2D woven C/SiC composite under mechanical loading. I. Mechanical characterization. Compos. Sci. Technol. 56, 1363–1372. Cao, H.C., Bischoff, E., Sbaizero, O., Ruhle, M., Evans, A.G., ¨ Marshall, D.B., Brennan, J.J., 1990. Effect of interfaces on the properties of fiber-reinforced ceramics. J. Am. Ceram. Soc. 73 (6), 1691–1699. Chiang, Y.M., Haggerty, J.S., Messner, R.P., Demetry, C., 1989. Reaction-based processing methods for ceramic-matrix composites. Am. Ceram. Soc. Bull. 68 (2), 420– 428. Christin, F., 2002. Design, fabriction, and application of thermostructural composites (TSC) like C/C, C/SiC, and SiC/SiC composites. Adv. Eng. Mater. 4 (12), 903–912. Krenkel, W., Berndt, F., 2005. C/C–SiC composites for space applications and advanced friction systems. Mater. Sci. Eng. A 412, 177–181. Lacoste, M., Lacombe, A., Joyez, P., 2002. Carbon/carbon extendible nozzles. Acta Astronaut. 50 (6), 357–367. Lomov, S.V., Belov, E.B., Bischoff, T., Ghosh, S.B., Truong Chi, T., Verpoest, I., 2002. Carbon composites based on multiaxial