October 2007 Tensile Mechanical Properties of Ceramic Matrix Composites 3193 matrix cracks. In addition, above the cracking stress, composite Acknowledgments properties such as modulus and thermal conductivity also de- grade in complex and unpredictable ways. Thus, today most would like to thank Wayne Steffier of Hyper- Therm Composites or provision of the excellent property database of the various CMCs that CMC designers of nonoxide CMc components that require ng service life find it more desirable to achieve as high a crack ing stress as possible in the principal stress directions, but still References retain some comfortable level of ultimate strength. As shown in his study, this goal can best be achieved by increasing the effec ceedings of the the properties o f fibre composites Conference. pp. 15-24. IPC Sci- attempt to minimize the size and volume fraction of minicom- Several Ceramic-Matrix Composites,"JAm ceran posites oriented perpendicular to these directions. For thos cases where perpendicular minicomposites cannot be avoided Aging on the Mechanical Properties of a Porous-Matrix Ceramic Composite, lorscher and R. T. Bhatt. "Sic mechanistic-based mini-matrix approach can be helpful in un- derstanding and modeling matrix cracking for a variety of 2D Chap and 3D fiber architectures. It should also be noted that the PH M. Yun, J. Z. Gyekenyesi, Y.LChen,DR.Wheeler, and J.A.DiCarlo effects of creep rupture on fiber orientation need to be deter- Fibers. "Ceran. Eng. Sci. Proc. 22.521-3(2001 Reinforced by Treated Sylramic Sic mined and considered as well before deciding on a fiber archi- tecture and fiber orientation ven SiC/SiC Composite, "Comp. Sci. Technol, 59, 687-9(1999 N. Morscher. ""Stress-Dependent Matrix CI Reinforced Melt-Infiltrated SiC Matrix Composites, Comp. Sci. Tecno, 64, V. Summary and Conclusions Test Specimens at Ambient Temperature. ASTM, West Conshohocken, PA, (2000) A 2D-woven 0/90 and a 2D-braided [0/+67 Sylramic-iBN-re- s. Kalluri, A. Calomino, and D N. Brewer, "An Assessment of Variability in gle symmetrically located between the two primary fiber di- Eng. Sei Pr lensile pr nforced MI SiC matrix panel when tensile tested in-plane at an the A 用 (2004 Mel-Infiltrated SiC/SiC Composite,"Ceram rections were both shown to exhibit high stress for the onset of N. Morscher and V. Pujar, ""Melt-Infiltrated SiC Composites for Gas Tur- TTMC. The matrix cracking and deflection from linearity stress- Land, Sea, and Air, Ju 17, 2004, Vienna, Austria, Paper no. GT2004-5423 es were actually higher for the off-axis loading condition com- pared with 2D-woven [0/90] panels loaded in one of the primary Sic/SiC Composites. eram.Soe,214-152777880200 fiber directions. For both panels, this improved cracking behav. B. N. Cox and D. B. Marshall. "Crack Initiation in Fiber-Reinforced Brittle Laminates, " J. An. Ceram. Soc. 79 [5]1181-88(1996). ior can be explained in part by a higher effective fraction of fi- 3G. N. Morscher. "Modal Acoustic Emission Source Determination in Silicon bers in the loading direction, which reduces internal stress on Review te stress. For the woven ondestructive Evaluation. Edited by D. O. Thompson, and D. E Chimenti CP panel, there also existed an absence of weak minicomposit IG. N. Morscher"Matrix Cracking in Four Different 2D SiC/SiC Composite oriented perpendicular to the loading direction. For the braided ystems. Published in the 35th International SAMPE panel, which did have a low fraction of axial minicomposit ites were well separated from one another, which prevented the ig n morsch deling the Elastic Modulus of 2D Woven CVI SiC occurrence of‘back-to-back”90° minicomposites that are the source of low-strength matrix cracks in 2D-woven [0/90)com- sis of Fiber-Reinforced posites with similar tow size. AE measurements on the braided 407-18 in ASM Engineered Materials Handbook. Vol 21: Composites. ASM also showed that the onset stress for ttmc and the K. Naik. P. S. Shemekar, and M. v Ire Behavior of woven cracking distribution with increasing stress behaved effectively in the same way as 2D-woven [0/90]composites when loaded in °p. L. Falzon and l. Herzberg,“ Mechanical of 2-D Braided Car- a primary fiber direction. Not only does this confirm that the weak minicomposites perpendicular to the loading direction are Properties of an All-Oxide Ceramic Composite, " J. Am. Ceram. cal sources of it should also enable So,820272l-30(1999) matrix"approach?to model and improve matrix cracking and Wayne Steffier Composite Data Sheets, Hyper- mposites Inc (2006 DFL stresses of CMC components with braided and other 2C. S. Lynch and A. G. Evans, "Effects of OfT-Ax the Tensile bu architectures Lamon. and Allix "Model of the Non In terms of in-plane UTS, the Syl-iBN/MI SiC composite Behavior of 2D SiC-SiC Chemical Vapor Infiltration Composites, J.Amm. Ceran. were found to be superior in both on-axis and off-axis behavior n comparison with other 2D ceramic composites in the NASAs Enabling Propulsion Materials Program literature with either fiber-dominated or matrix-dominated me- chanical behavior. The off-axis behavior can be attributed pri- 2G. N. Morscher and J. Z. Gyekenesi, "Room Temperature Tensile Behavior marily to the relatively high modulus and strength of the mI on Reinforced SiC Matrix Composite matrix, which carries significant load and to the high strength Ceram. Eng. Sci. Proc., 19[3]241-9(1998) of the Sylramic-iBN fiber that is retained during composite G. N. Morscher, H. M. Yun, and J. A. DiCarlo, " Matrix J.Am. Cerami.Soc,88l]146-53(2005matrix cracks. In addition, above the cracking stress, composite properties such as modulus and thermal conductivity also de￾grade in complex and unpredictable ways. Thus, today most CMC designers of nonoxide CMC components that require long service life find it more desirable to achieve as high a crack￾ing stress as possible in the principal stress directions, but still retain some comfortable level of ultimate strength. As shown in this study, this goal can best be achieved by increasing the effec￾tive fiber fraction in these directions, but in doing so, one should attempt to minimize the size and volume fraction of minicom￾posites oriented perpendicular to these directions. For those cases where perpendicular minicomposites cannot be avoided, this and other studies7,27 have shown that the fairly robust mechanistic-based mini-matrix approach can be helpful in un￾derstanding and modeling matrix cracking for a variety of 2D and 3D fiber architectures. It should also be noted that the effects of creep rupture on fiber orientation need to be deter￾mined and considered as well before deciding on a fiber archi￾tecture and fiber orientation. V. Summary and Conclusions A 2D-woven 0/90 and a 2D-braided [0/767] Sylramic-iBN-re￾inforced MI SiC matrix panel when tensile tested in-plane at an angle symmetrically located between the two primary fiber di￾rections were both shown to exhibit high stress for the onset of TTMC. The matrix cracking and deflection from linearity stress￾es were actually higher for the off-axis loading condition com￾pared with 2D-woven [0/90] panels loaded in one of the primary fiber directions. For both panels, this improved cracking behav￾ior can be explained in part by a higher effective fraction of fi- bers in the loading direction, which reduces internal stress on critical matrix flaws for a given composite stress. For the woven panel, there also existed an absence of weak minicomposites oriented perpendicular to the loading direction. For the braided panel, which did have a low fraction of axial minicomposites loaded perpendicular to the loading direction, the minicompos￾ites were well separated from one another, which prevented the occurrence of ‘‘back-to-back’’ 901 minicomposites that are the source of low-strength matrix cracks in 2D-woven [0/90] com￾posites with similar tow size. AE measurements on the braided panel also showed that the onset stress for TTMC and the cracking distribution with increasing stress behaved effectively in the same way as 2D-woven [0/90] composites when loaded in a primary fiber direction. Not only does this confirm that the weak minicomposites perpendicular to the loading direction are the critical sources of, it should also enable use of the ‘‘mini￾matrix’’ approach7 to model and improve matrix cracking and DFL stresses of CMC components with braided and other architectures. In terms of in-plane UTS, the Syl-iBN/MI SiC composites were found to be superior in both on-axis and off-axis behavior in comparison with other 2D ceramic composites in the literature with either fiber-dominated or matrix-dominated me￾chanical behavior. The off-axis behavior can be attributed pri￾marily to the relatively high modulus and strength of the MI matrix, which carries significant load, and to the high strength of the Sylramic-iBN fiber that is retained during composite processing. Acknowledgments We would like to thank Wayne Steffier of Hyper-Therm Composites Incor￾porated for provision of the excellent property database of the various CMCs that they fabricate. References 1 J. Aveston, G. A. Cooper, and A. Kelly, Single and Multiple Fracture. Pro￾ceedings of the the Properties of Fibre Composites Conference, pp. 15–24. IPC Sci￾ence and Tech. Press Ltd., Guildford, Surrey, UK, 1971. 2 C. Cady, F. E. Heredia, and A. G. Evans, ‘‘In-Plane Mechanical Properties of Several Ceramic-Matrix Composites,’’ J. Am. Ceram. Soc., 78 [8] 2065–78 (1995). 3 E. A. V. Carelli, H. Fujita, J. Y. Yang, and F. W. Zok, ‘‘Effects of Thermal Aging on the Mechanical Properties of a Porous-Matrix Ceramic Composite,’’ J. Am. Ceram. Soc., 85 [3] 595–602 (2002). 4 J. A. DiCarlo, H.-M. Yun, G. N. Morscher, and R. T. Bhatt, ‘‘SiC/SiC Com￾posites for 12001C and Above’’; pp. 77–98 in Handbook of Ceramics Composites. Chapter 4, Edited by N. Bansal. Kluwer Academic, New York, NY, 2005. 5 H. M. Yun, J. Z. Gyekenyesi, Y. L. Chen, D. R. Wheeler, and J. A. DiCarlo, ‘‘Tensile Behavior of SiC/SiC Composites Reinforced by Treated Sylramic SiC Fibers,’’ Ceram. Eng. Sci. Proc., 22, 521–3 (2001). 6 G. N. Morscher, ‘‘Modal Acoustic Emission of Damage Accumulation in a Woven SiC/SiC Composite,’’ Comp. Sci. Technol., 59, 687–9 (1999). 7 G. N. Morscher, ‘‘Stress-Dependent Matrix Cracking in 2D Woven SiC-Fiber Reinforced Melt-Infiltrated SiC Matrix Composites,’’ Comp. Sci. Technol., 64, 1311–9 (2004). 8 ASTM C-1275. Standard Test Method for Monotonic Tensile Behavior of Con￾tinuous Fiber-Reinforced Advanced Ceramics with Solid Rectangular Cross-Section Test Specimens at Ambient Temperature. ASTM, West Conshohocken, PA, (2000). 9 S. Kalluri, A. Calomino, and D. N. Brewer, ‘‘An Assessment of Variability in the Average Tensile Properties of a Melt-Infiltrated SiC/SiC Composite,’’ Ceram. Eng. Sci. Proc., 25 [4] 79–86 (2004). 10G. N. Morscher and V. Pujar, ‘‘Melt-Infiltrated SiC Composites for Gas Tur￾bine Engine Applications’’; Proceedings of ASME Turbo Expo 2004: Power for Land, Sea, and Air, June 14–17, 2004, Vienna, Austria, Paper no. GT2004-54233. 11G. N. Morscher and J. D. Cawley, ‘‘Intermediate Temperature Strength De￾gradation in SiC/SiC Composites,’’ Eur. Ceram. Soc., 22 [14–15] 2777–88 (2002). 12B. N. Cox and D. B. Marshall, ‘‘Crack Initiation in Fiber-Reinforced Brittle Laminates,’’ J. Am. Ceram. Soc., 79 [5] 1181–88 (1996). 13G. N. Morscher, ‘‘Modal Acoustic Emission Source Determination in Silicon Carbide Matrix Composites’’; pp. 383–90 in Review of Progress in Quantitative Nondestructive Evaluation, Edited by D. O. Thompson, and D. E. Chimenti. CP 509, American Institute of Physics, 2000. 14G. N. Morscher ‘‘Matrix Cracking in Four Different 2D SiC/SiC Composite Systems,’’ Published in the 35th International SAMPE Technical Conference Pro￾ceedings (CD), Dayton, OH (2003). 15R. M. Jones, Mechanics of Composite Materials, pp. 54. Hemisphere Publish￾ing Corp, New York, 1975. 16G. N. Morscher, ‘‘Modeling the Elastic Modulus of 2D Woven CVI SiC Composites,’’ Comp. Sci. Int., 66 [15] 2804–1 (2006). 17F. W. Zok, ‘‘Fracture Analysis of Fiber-Reinforced Ceramic Composites’’; pp. 407–18 in ASM Engineered Materials Handbook. Vol. 21: Composites. ASM, Materials Park, OH, 2001. 18N. K. Naik, P. S. Shemekar, and M. V. Hosur, ‘‘Failure Behavior of Woven Fabric Composites,’’ J. Comp. Technol. Res., 13 [2] 107–16 (1991). 19P. J. Falzon and I. Herzberg, ‘‘Mechanical Performance of 2-D Braided Car￾bon/Epoxy Composites,’’ Comp. Sci. Technol., 58, 253–65 (1998). 20J. A. Heathcote, X. Y. Gong, J. Yang, U. Ramamurty, and F. W. Zok, ‘‘In￾Plane Mechanical Properties of an All-Oxide Ceramic Composite,’’ J. Am. Ceram. Soc., 82 [10] 2721–30 (1999). 21Wayne Steffier Composite Data Sheets, Hyper-Therm Composites Inc. (2006) 22C. S. Lynch and A. G. Evans, ‘‘Effects of Off-Axis Loading on the Tensile Be￾havior of a Ceramic-Matrix Composite,’’ J. Am. Ceram. Soc., 79 [12] 3113–23 (1996). 23X. Aubard, J. Lamon, and O. Allix, ‘‘Model of the Nonlinear Mechanical Behavior of 2D SiC–SiC Chemical Vapor Infiltration Composites,’’ J. Am. Ceram. Soc., 77 [18] 2118–26 (1994). 24 Unpublished Data from NASA’s Enabling Propulsion Materials Program. 25G. N. Morscher, Unpublished Research Based on Unload-Reload Tests Per￾formed at 8151C 26G. N. Morscher and J. Z. Gyekenesi, ‘‘Room Temperature Tensile Behavior and Damage Accumulation of Hi-Nicalon Reinforced SiC Matrix Composites,’’ Ceram. Eng. Sci. Proc., 19 [3] 241–9 (1998). 27G. N. Morscher, H. M. Yun, and J. A. DiCarlo, ‘‘Matrix Cracking in 3D Orthogonal Melt-Infiltrated SiC/SiC Composites with Various Z-Fiber Types,’’ J. Am. Ceram. Soc., 88 [1] 146–53 (2005). & October 2007 Tensile Mechanical Properties of Ceramic Matrix Composites 3193