480A.DiCarloetal./Appl.Mat.Comput.152(2004)473 rupture [ 15]. Unlike the Nicalon composite of Shi et al. [12], there was no clear evidence that allowed an understanding of which constituent ruptured first or what mechanism controlled final rupture. However, if one plots minimum composite creep rates versus the times at initiation of the tertiary stage, the two data points in Fig. 2 show typical results. Since both the Sylramic fiber line at 1200C and the CvI Sic line at 1300C move up with a temperature in crease to 1315C, the fact that the Sylramic composite data points fall closer the estimated MG line for the CVI SiC matrix would suggest that the matrix rather than the Sylramic fiber was responsible for composite rupture. Clearly more studies are needed to validate the accuracy of this condition(A)model Nevertheless, the position of the Fig. 2 MG line for the Ultra-SCS fiber, even at 1200C, would suggest that the rupture lives of these Sic/Sic composites could be significantly improved at any creep rate (or composite stress or constituent olume fraction)if CVI SiC matrices could be developed that displayed a more stoichiometric composition than current versions 4. Summary and conclusions This paper has shown that the high-temperature fracture of Sic/Sic com- posites is primarily controlled by creep-induced flaw growth in the Sic fibers and matrices. Thus for composite applications requiring long service life, it is very important to reduce effects that enhance constituent creep both from within the microstructure(small grains, impurity phases) and from within the application(high stress, high temperature, inert environment). Despite these complicating factors, it is also shown that empirical rupture models, based on fiber and matrix Monkman-Grant diagrams, offer a simple approach for mechanistic analysis and prediction of creep-induced rupture for Sic/SiC composites and ceramic composites in general References [D. Brewer, Mater. Sci. Eng. A261(1999)284 [2T. Kameda, Y. Itoh, T. Hijikata, T. Okamura, in: Proceedings of the International Gas Turbine& Aeroengine Congress. The American Society of Mechanical Engineers. New York, NY,2000( Paper2000-GT-67) H Ichikawa, T Ishikawa. in: A. Kelly, C Zweben, T Chou(Eds ) Comprehensive Composite Materials, vol. 1, Elsevier Science Ltd, Oxford, England, 2000. Pp. 107-14 4R. E. Tressler, J.A. DiCarlo, in: R. Naslain, J. Lamon, D. Doumeingts(Eds ) Proceedings of HT-CMC-l Woodland Publishing Ltd, Cambridge, England, 1993 Proceedings of HT-CMC-2, Ceramic Transactions, vol. 57, 1993, p. 141, pp 33-49 [H.M. Yun, J.C. Goldsby, J.A. DiCarlo, in: Advances in Ceramic Matrix Composites Il. Ceramic Transactions, vol 46, 1994, p. 17 [6 H M. Yun, J.C. Goldsby, J.A. DiCarlo, in: Proceedings for HTCMC-2, Ceramic Transactions, o.57,1995,p.331rupture [15]. Unlike the Nicalon composite of Shi et al. [12], there was no clear evidence that allowed an understanding of which constituent ruptured first or what mechanism controlled final rupture. However, if one plots minimum composite creep rates versus the times at initiation of the tertiary stage, the two [D] data points in Fig. 2 show typical results. Since both the Sylramic fiber line at 1200
C and the CVI SiC line at 1300
C move up with a temperature in￾crease to 1315
C, the fact that the Sylramic composite data points fall closer to the estimated MG line for the CVI SiC matrix would suggest that the matrix rather than the Sylramic fiber was responsible for composite rupture. Clearly more studies are needed to validate the accuracy of this condition (A) model. Nevertheless, the position of the Fig. 2 MG line for the Ultra-SCS fiber, even at 1200
C, would suggest that the rupture lives of these SiC/SiC composites could be significantly improved at any creep rate (or composite stress or constituent volume fraction) if CVI SiC matrices could be developed that displayed a more stoichiometric composition than current versions. 4. Summary and conclusions This paper has shown that the high-temperature fracture of SiC/SiC com￾posites is primarily controlled by creep-induced flaw growth in the SiC fibers and matrices. Thus for composite applications requiring long service life, it is very important to reduce effects that enhance constituent creep both from within the microstructure (small grains, impurity phases) and from within the application (high stress, high temperature, inert environment). Despite these complicating factors, it is also shown that empirical rupture models, based on fiber and matrix Monkman–Grant diagrams, offer a simple approach for mechanistic analysis and prediction of creep-induced rupture for SiC/SiC composites and ceramic composites in general. References [1] D. Brewer, Mater. Sci. Eng. A261 (1999) 284. [2] T. Kameda, Y. Itoh, T. Hijikata, T. Okamura, in: Proceedings of the International Gas Turbine & Aeroengine Congress, The American Society of Mechanical Engineers, New York, NY, 2000 (Paper 2000-GT-67). [3] H. Ichikawa, T. Ishikawa, in: A. Kelly, C. Zweben, T. Chou (Eds.), Comprehensive Composite Materials, vol. 1, Elsevier Science Ltd., Oxford, England, 2000, pp. 107–145. [4] R.E. Tressler, J.A. DiCarlo, in: R. Naslain, J. Lamon, D. Doumeingts (Eds.), Proceedings of HT-CMC-1, Woodland Publishing Ltd., Cambridge, England, 1993; Proceedings of HT-CMC-2, Ceramic Transactions, vol. 57, 1993, p. 141, pp. 33–49. [5] H.M. Yun, J.C. Goldsby, J.A. DiCarlo, in: Advances in Ceramic Matrix Composites II, Ceramic Transactions, vol. 46, 1994, p. 17. [6] H.M. Yun, J.C. Goldsby, J.A. DiCarlo, in: Proceedings for HTCMC-2, Ceramic Transactions, vol. 57, 1995, p. 331. 480 J.A. DiCarlo et al. / Appl. Math. Comput. 152 (2004) 473–481