Oxide CMCs are not susceptible to embrittlement. But polycrystalline oxide fibers have inferior creep strength. New approaches for creep strengthening of oxide polycrystals must be implemented in order to create oxide CMCs having desirable creep resistance above 1200 °C. Relatively low thermal conductivity, especially at high temperatures, remains a problem. But there are no obvious solutions to enhancing thermal conductivity while also trying to attain good creep resistance. Design strategies that disperse heat fluxes and control the temperature excursions, such as thermal barrier coatings, may be required.

REFERENCES

1. H.R. Bakis , N.R. Yih , W.W. Stinchcomb , and K.L. Reifsnider , “Damage Initiation and Growth in Notched Laminates Under Reversed Cyclic Loading,” ASTM STP 1012 , American Society of Testing and Materials , Philadelphia, Pa. , pp. 66-83 ( 1989 ).

2. W.W. Stinchcomb and E. Bakis , Fatigue of Composite Materials, edited by K.L. Reifsnider , Elsevier Science , New York , pp. 105-80 ( 1990 ).

3. T.J. Mackin , K.E. Perry , J.S. Epstein , C. Cady , and A.G. Evans , “Strain Fields and Damage Around Notches in Ceramic-Matrix Composites, ” J. Am. Ceram. Soc., 79 , 65-73 ( 1996 ).

4. T.J. Mackin , T.E. Purcell , M.Y. He , and A.G. Evans , “Notch Sensitivity and Stress Redistribution in Three Ceramic-Matrix Composites,” J. Am. Ceram. Soc., 78 , 1719-1728 ( 1995 ).

5. C. Cady , A.G. Evans , and K.E. Perry, Jr. , “Stress Redistribution Around Mechanical Attachments in Ceramic Matrix Composites,” Composites, 26 , 683-690 ( 1995 ).

6. C.M. Cady , T.J. Mackin , and A.G. Evans , “Silicon Carbide/Calcium Aluminosilicate: A Notch-Insensitive Ceramic-Matrix Composite,” J. Am. Ceram. Soc., 78 , 77-82 ( 1995 ).

7. F.E. Heredia , S.M. Spearing , T.J. Mackin , M.Y. He , A.G. Evans , P. Mosher , and P. Brondsted , “Notch Effects in Carbon Matrix Composites,” J. Am. Ceram. Soc., 77 , 2817-2827 ( 1994 ).

8. A.G. Evans and F.W. Zok , “Notch Effects in Carbon Matrix Composites,” Solid State Physics, 47 , 177-286 ( 1994 ).

9. G. Genin and J.W. Hutchinson , “High Temperature Ceramic-Matrix Composites II,” J. Am. Ceram. Soc., inpress .

10. T.J. Lu , J.W. Hutchinson , and A.G. Evans , “A Steady-State Furnace Analysis for Technical Cost Modeling of Heat Treated Products,” J. Am. Ceram. Soc., inpress .

11. M.F. Ashby , Materials Selection in Mechanical Design, Pergamon Press , New York ( 1988 ).

12. Cambridge Materials Selector (CMS) , Granta Design , Cambridge, UK ( 1994 ). ( CMS is a Windows-based PC toolkit for the evaluation and selection of materials for engineering design .)

13. A.C.F. Cocks , S. Jansson , and F.A. Leckie , “Effect of Cyclic Thermal Loading on the Properties of Metal Matrix Composites,” J. Therm. Stress, 15 , 175-184 ( 1992 ).

14. T.C. Lu , J. Yang , Z. Suo , A.G. Evans , R. Hecht , and R. Mehrabian , “Matrix Cracking in Intermetallic Composites Caused by Thermal Expansion Mismatch,” Acta Metall. Mater., 39 , 1883-1890 ( 1991 ).

15. A.G. Evans , “Ceramics and Ceramic Composites as High-Temperature Structural Materials: Challenges and Opportunities,” Philos. Trans. R. Soc. London, Ser. A, 315 , 511-525 ( 1995 ).

16. J.W. Hutchinson , Non-Linear Fracture Mechanics, Technical University of Denmark , Lyngby, Denmark ( 1980 ).

17. S.R. Gunawardena , S. Jansson , and F.A. Leckie , “Transverse Ductility of Metal Matrix Composites,” Acta Metall. Mater., 41 ( 1993 ).

18. F.A. Leckie , “High-Temperature Mechanism-Based Design,” Philos. Trans. R. Soc. London, Ser. A, 315 , 611-623 ( 1995 ).

19. B.N. Cox and C.S. Lo , “Load Ratio, Notch, and Scale Effects for Bridged Cracks in Fibrous Composites,” Acta Metall. Mater., 40 , 69-80 ( 1992 ).

20. G. Bao and Z. Suo , “Remarks on Crack-Bridging Concepts,” Appl. Mech. Rev., 45 , 355-356 ( 1992 ).

21. B.N. Cox , “Extrinsic Factors in the Mechanics of Bridged Cracks,” Acta Metall. Mater., 39 , 1189-1201 ( 1991 ).

22. D.B. Marshall , B.N. Cox , and A.G. Evans , “The Mechanics of Matrix Cracking in Brittle-Matrix Fiber Composites, ” Acta Metall. Mater., 33 , 2013 ( 1985 ).

23. F.W. Zok , Z.Z. Du , and S.J. Connell , “On the Development of Fatigue Failure Maps for Titanium Matrix Composites, ” Mater. Sci. Eng., A200 , 103-113 ( 1995 ).

24. A.G. Evans , “Perspective on the Development of High-Toughness Ceramics,” J. Am. Ceram. Soc., 73 , 187-206 ( 1990 ).

25. B.R. Lawn , Fracture of Brittle Solids, Cambridge Press , New York ( 1993 ).

26. A.G. Evans , “Design and Life Prediction Issues for High-Temperature Engineering Ceramics and Their Composites,” Acta Metall. Mater., 45 , 23-40 ( 1997 ).

27. A. Freudenthal , “Statistical Approach to Brittle Fracture,” in Fracture, edited by H. Liebowitz , Academic Press , San Diego, Calif. , pp. 519-619 ( 1968 ).

28. J.R. Matthews , W.J. Shack , and F.A. McClinktock , “Statistical Determination of Surface Flow Density in Brittle Materials, ” J. Am. Ceram. Soc., 59 , 304 ( 1976 ).

29. D.A.W. Kaute , J.R. Shercliff , and M.F. Ashby , “Delamination, Fibre Bridging and Toughness of Ceramic Matrix Composites, ” Acta Metall. Mater., 41 , 1959-1970 ( 1993 ).



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OCR for page 23
IMPLEMENTATION CHALLENGES FOR HIGH-TEMPERATURE COMPOSITES Oxide CMCs are not susceptible to embrittlement. But polycrystalline oxide fibers have inferior creep strength. New approaches for creep strengthening of oxide polycrystals must be implemented in order to create oxide CMCs having desirable creep resistance above 1200 °C. Relatively low thermal conductivity, especially at high temperatures, remains a problem. But there are no obvious solutions to enhancing thermal conductivity while also trying to attain good creep resistance. Design strategies that disperse heat fluxes and control the temperature excursions, such as thermal barrier coatings, may be required. REFERENCES 1. H.R. Bakis , N.R. Yih , W.W. Stinchcomb , and K.L. Reifsnider , “Damage Initiation and Growth in Notched Laminates Under Reversed Cyclic Loading,” ASTM STP 1012 , American Society of Testing and Materials , Philadelphia, Pa. , pp. 66-83 ( 1989 ). 2. W.W. Stinchcomb and E. Bakis , Fatigue of Composite Materials, edited by K.L. Reifsnider , Elsevier Science , New York , pp. 105-80 ( 1990 ). 3. T.J. Mackin , K.E. Perry , J.S. Epstein , C. Cady , and A.G. Evans , “Strain Fields and Damage Around Notches in Ceramic-Matrix Composites, ” J. Am. Ceram. Soc., 79 , 65-73 ( 1996 ). 4. T.J. Mackin , T.E. Purcell , M.Y. He , and A.G. Evans , “Notch Sensitivity and Stress Redistribution in Three Ceramic-Matrix Composites,” J. Am. Ceram. Soc., 78 , 1719-1728 ( 1995 ). 5. C. Cady , A.G. Evans , and K.E. Perry, Jr. , “Stress Redistribution Around Mechanical Attachments in Ceramic Matrix Composites,” Composites, 26 , 683-690 ( 1995 ). 6. C.M. Cady , T.J. Mackin , and A.G. Evans , “Silicon Carbide/Calcium Aluminosilicate: A Notch-Insensitive Ceramic-Matrix Composite,” J. Am. Ceram. Soc., 78 , 77-82 ( 1995 ). 7. F.E. Heredia , S.M. Spearing , T.J. Mackin , M.Y. He , A.G. Evans , P. Mosher , and P. Brondsted , “Notch Effects in Carbon Matrix Composites,” J. Am. Ceram. Soc., 77 , 2817-2827 ( 1994 ). 8. A.G. Evans and F.W. Zok , “Notch Effects in Carbon Matrix Composites,” Solid State Physics, 47 , 177-286 ( 1994 ). 9. G. Genin and J.W. Hutchinson , “High Temperature Ceramic-Matrix Composites II,” J. Am. Ceram. Soc., inpress . 10. T.J. Lu , J.W. Hutchinson , and A.G. Evans , “A Steady-State Furnace Analysis for Technical Cost Modeling of Heat Treated Products,” J. Am. Ceram. Soc., inpress . 11. M.F. Ashby , Materials Selection in Mechanical Design, Pergamon Press , New York ( 1988 ). 12. Cambridge Materials Selector (CMS) , Granta Design , Cambridge, UK ( 1994 ). ( CMS is a Windows-based PC toolkit for the evaluation and selection of materials for engineering design .) 13. A.C.F. Cocks , S. Jansson , and F.A. Leckie , “Effect of Cyclic Thermal Loading on the Properties of Metal Matrix Composites,” J. Therm. Stress, 15 , 175-184 ( 1992 ). 14. T.C. Lu , J. Yang , Z. Suo , A.G. Evans , R. Hecht , and R. Mehrabian , “Matrix Cracking in Intermetallic Composites Caused by Thermal Expansion Mismatch,” Acta Metall. Mater., 39 , 1883-1890 ( 1991 ). 15. A.G. Evans , “Ceramics and Ceramic Composites as High-Temperature Structural Materials: Challenges and Opportunities,” Philos. Trans. R. Soc. London, Ser. A, 315 , 511-525 ( 1995 ). 16. J.W. Hutchinson , Non-Linear Fracture Mechanics, Technical University of Denmark , Lyngby, Denmark ( 1980 ). 17. S.R. Gunawardena , S. Jansson , and F.A. Leckie , “Transverse Ductility of Metal Matrix Composites,” Acta Metall. Mater., 41 ( 1993 ). 18. F.A. Leckie , “High-Temperature Mechanism-Based Design,” Philos. Trans. R. Soc. London, Ser. A, 315 , 611-623 ( 1995 ). 19. B.N. Cox and C.S. Lo , “Load Ratio, Notch, and Scale Effects for Bridged Cracks in Fibrous Composites,” Acta Metall. Mater., 40 , 69-80 ( 1992 ). 20. G. Bao and Z. Suo , “Remarks on Crack-Bridging Concepts,” Appl. Mech. Rev., 45 , 355-356 ( 1992 ). 21. B.N. Cox , “Extrinsic Factors in the Mechanics of Bridged Cracks,” Acta Metall. Mater., 39 , 1189-1201 ( 1991 ). 22. D.B. Marshall , B.N. Cox , and A.G. Evans , “The Mechanics of Matrix Cracking in Brittle-Matrix Fiber Composites, ” Acta Metall. Mater., 33 , 2013 ( 1985 ). 23. F.W. Zok , Z.Z. Du , and S.J. Connell , “On the Development of Fatigue Failure Maps for Titanium Matrix Composites, ” Mater. Sci. Eng., A200 , 103-113 ( 1995 ). 24. A.G. Evans , “Perspective on the Development of High-Toughness Ceramics,” J. Am. Ceram. Soc., 73 , 187-206 ( 1990 ). 25. B.R. Lawn , Fracture of Brittle Solids, Cambridge Press , New York ( 1993 ). 26. A.G. Evans , “Design and Life Prediction Issues for High-Temperature Engineering Ceramics and Their Composites,” Acta Metall. Mater., 45 , 23-40 ( 1997 ). 27. A. Freudenthal , “Statistical Approach to Brittle Fracture,” in Fracture, edited by H. Liebowitz , Academic Press , San Diego, Calif. , pp. 519-619 ( 1968 ). 28. J.R. Matthews , W.J. Shack , and F.A. McClinktock , “Statistical Determination of Surface Flow Density in Brittle Materials, ” J. Am. Ceram. Soc., 59 , 304 ( 1976 ). 29. D.A.W. Kaute , J.R. Shercliff , and M.F. Ashby , “Delamination, Fibre Bridging and Toughness of Ceramic Matrix Composites, ” Acta Metall. Mater., 41 , 1959-1970 ( 1993 ).

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IMPLEMENTATION CHALLENGES FOR HIGH-TEMPERATURE COMPOSITES 30. S.M. Spearing and A.G. Evans , “The Role of Fiber Bridging in the Delamination Resistance of Fiber-Reinforced Composites,” Acta Metall. Mater., 40 , 2191-2199 ( 1992 ). 31. F.A. Heredia , M.Y. He , and A.G. Evans , “Mechanical Performances of Ceramic Matrix Composite I-Beams,” Composites, 27A , 1157-1167 ( 1996 ). 32. S. Jansson and F.A. Leckie , “Transverse Tensile and Inplane Shear Strength of Weakly Bonded Fiber Reinforced MMC's Subjected to Cyclic Thermal Loading,” Mech. Mater., 18 , 205-212 ( 1994 ). 33. A. Burr , J. Yang , C.G. Levi , and F.A. Leckie , “The Strength of Metal-Matrix Composite Joints,” Acta Metall. Mater., 43 , 3361-3373 ( 1995 ). 34. F.W. Zok , M.Y. He , A.G. Evans , F.A. Leckie , and H.E. Deve , “Strength-Limited Design of Composite/Monolith Transitions in Metallic Structures,” Composites, 28A , 399-407 ( 1997 ). 35. John Busch , IBIS Associates , Wellesley, Mass. , private communication, May 1996 . 36. R. Anderson , Pratt and Whitney , West Palm Beach, Fla. , private communication, January 1996 . 37. W. Tu , F.F. Lange , and A.G. Evans , “Concept for a Damage-Tolerant Ceramic Composite with ‘Strong' Interfaces,” J. Am. Ceram. Soc., 79 , 417-24 ( 1996 ). 38. W.A. Curtin , “Theory of Mechanical Properties of Ceramic-Matrix Composites,” J. Am. Ceram. Soc., 74 , 2837-2845 ( 1991 ). 39. Z.Z. Du and R.M. McMeeking , “Control of Strength Anisotropy of Metal Matrix Fiber Composites,” J. Computer-Aided Mater. Design, 1 , 243-264 ( 1994 ). 40. J.W. Hutchinson and H. Jensen , “Models of Fiber Debonding and Pullout in Brittle Composites with Friction,” Mech. Mater., 9 , 139 ( 1990 ). 41. W.A. Curtin , “Fiber Pull-Out and Strain Localization in Ceramic Matrix Composites, ” J. Mech. Phys. Solids, 41 , 217-245 ( 1993 ). 42. M.Y. He , A.G. Evans , and W.A. Curtin , “The Ultimate Tensile Strength of Metal and Ceramic-Matrix Composites, ” Acta Metall. Mater., 41 , 871-878 ( 1993 ). 43. S.L. Phoenix , “Statistical Issues in the Fracture of Brittle-Matrix Fibrous Composites, ” Compos. Sci. Technol., 48 , 65-80 ( 1993 ). 44. R.B. Henstenburg and S.L. Phoenix , “Interfacial Shear Strength Studies Using the Single-Filament-Composite Test. II. A Probability Model and Monte Carlo Simulation,” Polym. Compos., 10 , 389-408 ( 1989 ). 45. S.L. Phoenix and R. Raj , “Scalings in Fracture Probabilities for a Brittle Matrix Fiber Composite, ” Acta Metall. Mater., 40 , 2813-2828 ( 1992 ). 46. T.J. Kotil , J.W. Holmes , and M. Comninou , “Origin of Hysteresis Observed During Fatigue of Ceramic-Matrix Composites, ” J. Am. Ceram. Soc., 73 , 1879 ( 1990 ). 47. J.M. Domergue , E. Vagaggini , and A.G. Evans , “Relationships Between Hysteresis Measurements and the Constituent Properties of Ceramic Matrix Composites: II. Experimental Studies on Unidirectional Materials,” J. Am. Ceram. Soc., 78 , 2721-2731 ( 1995 ). 48. A.G. Evans , J.M. Domergue and E. Vagaggini , “Methodology for Relating the Tensile Constitutive Behavior of Ceramic-Matrix Composites to Constituent Properties,” J. Am. Ceram. Soc., 77 , 1425-1435 ( 1994 ). 49. M. Ibnabdeljalil and W.A. Curtin , “Strength and Reliability of Fiber-reinforced Composites: Localized Load Sharing and Associated Side Effects,” to be published in International Journal of Solids and Structures. 50. Z.C. Xia , J.W. Hutchinson , A.G. Evans , and B. Budiansky , “On Large Scale Sliding in Fiber-Reinforced Composites,” J. Mech. Phys. Solids, 42 , 1139-1158 ( 1994 ). 51. B. Budiansky and Y.L. Cui , “Toughening of Ceramics by Short Aligned Fibers,” Mech. Mater., 21 , 139-146 ( 1995 ). 52. G. Genin and J.W. Hutchinson , “High Temperature Ceramic Matrix Composites II,” J. Am. Ceram. Soc., in press . 53. C. Xia , R.R. Carr , and J.W. Hutchinson , “Transverse Cracking in Fiber-Reinforced Brittle Matrix, Cross-Ply Laminates,” Acta Metall. Mater., 41 , 2365 ( 1993 ). 54. C. Xia and J.W. Hutchinson , “Matrix Cracking of Cross-Ply Ceramic Composites,” Acta Metall. Mater., 42 , 1935-1945 ( 1994 ). 55. J.-M. Domergue , F.E. Heredia , and A.G. Evans , “Hysteresis Loops and the Inelastic Deformation of 0/90 Ceramic Matrix Composites,” J. Am. Ceram. Soc., 79 , 161-170 ( 1996 ). 56. F. Hild , A. Burr , and F.A. Leckie , “Matrix Cracking and Debonding of Ceramic-Matrix Composites,” Int. J. Solids Struct., 33 , 1209-1220 ( 1996 ). 57. M.Y. He , B.-X. Wu , A.G. Evans , and J.W. Hutchinson , “Inelastic Strains Due to Matrix Cracking in Unidirectional Fiber-Reinforced Composites,” Mech. Mater., 18 , 213-229 ( 1994 ). 58. S.K. Chan , M.Y. He , and J.W. Hutchinson , “Cracking and Stress Redistribution in Ceramic Layered Composites, ” Mater. Sci. Eng., A167 , 57-64 ( 1993 ). 59. D.K. Leung , M.Y. He , and A.G. Evans , “The Cracking Resistance of Nanoscale Layers and Films,” J. Mater. Res., 10 , 1693-1699 ( 1995 ). 60. M.C. Shaw , D.B. Marshall , B.J. Dalgleish , M.S. Dadkhah , M.Y. He , and A.G. Evans , “Fatigue Crack Growth and Stress Redistribution at Interfaces,” Acta Metall. Mater., 42 , 4091-4099 ( 1994 ). 61. P.K. Wright , R. Nimmer , G. Smith , M. Sensmeier , and M. Brun , “The Influence of the Interface on Mechanical Behavior of Ti6A14V/ SCS-6 Composites,” in Interfaces in Metal-Ceramics Composites, Anaheim, Calif. , February 18-22 , pp. 559-581 ( 1990 ). 62. S. Jansson , H. Deve , and A.G. Evans. , “Anisotropic Mechanical Properties of a Ti Matrix Composite Reinforced with SiC Fibers,” Metall. Trans., 22A , 2975-2983 ( 1991 ). 63. J. Neumeister , S. Jansson , and F.A. Leckie , “The Effect of Fiber Architecture on the Mechanical Properties of Carbon/Carbon Fiber Composites,” Acta Materialia, 44 , 573-585 ( 1996 ). 64. J.W. Hutchinson , T.J. Lu , and Z.C. Xia , “Delamination of Beams Under Transverse Shear and Bending,” Mater. Sci. Eng., A188 , 103-112 ( 1994 ).

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IMPLEMENTATION CHALLENGES FOR HIGH-TEMPERATURE COMPOSITES 65. J.W. Hutchinson and T.J. Lu , “Role of Fiber Stitching in Eliminating Transverse Fracture in Cross-Ply Ceramic Composites,” J. Am. Ceram. Soc., 78 , 251-253 ( 1995 ). 66. J.W. Hutchinson and T.J. Lu , “Laminate Delamination Due to Thermal Gradients,” J. Eng. Mater. Technol., 117 , 386-390 ( 1995 ). 67. B.N. Cox , R. Massabó , and K.T. Kedward , “Suppression of Delaminations in Curved Structures by Stitching,” Composites, Part A, 27A , 1133-1138 ( 1996 ). 68. A.G. Evans , F.W. Zok , and R.M. McMeeking , “Fatigue of Ceramic Matrix Composites,” Acta Metall. Mater., 43 , 859 ( 1995 ). 69. D. Rouby and P. Reynaud , “Fatigue Behaviour Related to Interface Modification During Load Cycling in Ceramic-Matrix Fibre Composites,” Compos. Sci. Technol., 48 , 109-118 ( 1993 ). 70. R.M. McMeeking and A.G. Evans , “Matrix Fatigue Cracking in Fiber Composites,” Mech. Mater., 9 , 217-227 ( 1990 ). 71. M. Sensmeier and K. Wright , “The Effect of Fiber Bridging on Fatigue Crack Growth in Titanium Matrix Composites,” in Fundamental Relationships Between Microstructures and Mechanical Properties of Metal-Matrix Composites ( P.K. Law and M.N. Gungor , eds.), Minerals, Metals, and Materials Society , Warrendale, Pa. , pp. 441-459 ( 1990 ). 72. C.J. Gilbert , R.H. Dauskardt , R.W. Steinbrech , R.N. Petrany , and R.O. Ritchie , “Cyclic Fatigue in Monolithic Alumina: Mechanisms for Crack Advance Promoted by Frictional Wear of Grain Bridges,” J. Mater. Sci., 30 , 643 ( 1995 ). 73. F.E. Heredia , J.C. McNulty , F.W. Zok , and A.G. Evans , “Oxidation Embrittlement Probe for Ceramic-Matrix Composites,” J. Am. Ceram. Soc., 78 , 2097-2100 ( 1995 ). 74. D.R. Walls , M. McNulty , and F.W. Zok , “Multiple Matrix Cracking in a Fiber-Reinforced Titanium Matrix Composite Under High Cycle Fatigue,” Metall. Mater. Trans., 27A , 1899-1907 ( 1996 ). 75. A.G. Evans , F.W. Zok , Z.Z. Du , and R.M. McMeeking , “Models of High Temperature, Environmentally Assisted Embrittlement in Ceramic-Matrix Composites,” J. Am. Ceram. Soc., 79 , 2345-2352 ( 1996 ).