February 200-4 Mullite/Alumina Mixtures for Use as Porous Matrices in Oxide Fiber Composite the property combinations lie within the domain of crack deflec References tion in the He and Hutchinson' diagram. These results reaffirm mullite-alumina mixtures as good candidate matrixes for use in C.G.Levi..Y,Yang.B,. Dalgleish, F. w. Zok, and A Gi. Evans, "Processing and Performance of an AIl-Oxide Ceramic Composite!".Ann. Ceram. Soc. 8I oa on extrapolation of the predictions in Fig 8 to 2-0-1. the oxide composites, even with rather high alumina content. M. A Mattoni and F w. Zok. to be published. M. A Mistloni, I. Y. Yang. C G. Levi, and F w. Zok."Eflects of Matrix Porosity ange from 4000 h for 60M/40A to 60 000 h for pure inL. Ceran. SN. 84 omparable to the targeted service times for CFCC comp A Heathcote, x.Y. Gong, J. Y: Yang U. Ramamurty and F. W.Zok, "In-Plane Based on the differences in t. matrixes with lower Mechanical Properties of an Al-Oxide Ceramic Composite. "J. An Cerum. Sor, 82 contents would be preferred 1012721-30(1999 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 Compcsite. "J, Am, Cerant G. Levi. F. W. Zok. J. Y. Yang. M. Mattoni, and J. P. A. Lofvandet Microstructural Design of Stable Porous Matrices for All-Oxide Ceramic Compos- ites," Z Mletallkd, 90 1121 1037. Mullite-alumina mixtures exhibit physical and mechanical char M-Y He and J W. Hutchinson, "Crack Deflection at an Interface betwee acteristics that make them attractive for use as porous matrixes in Dissimilar Elastic Materials. "Int. J. Soitds S9/991 LK251911053-6701989 Density of Composite Powder ' H. Fujita. G Jefferson, C. G. Levi, and F. w. Zok. "On the Use of an Alumina for alumina concentrations <20%, and combinations of modulus Precursor for Controlling the Mechanical Properties of Porous Mullite/Alumina and toughness that should lead to deflection of a matrix crack at a Am, Ceran Soc. in review uASTM Designation C 20-92. Book of ASTM Standards, American Society for fiber-matrix interface. The models of mechanical properties of Testing and Materials, West Conshohocken. PA. particle aggregates presented here coupled with the crack deflec- I Ceramic Souree h. The American Ceramie Society. Westerville. OH, 1990 tion parameter provide a means of extrapolating the experimental G. Tattersall and G. Tappin. "The Work of Fracture and Its Measurement in data to longer aging times, for the purpose of determining the M F, Ashby,"A First Report on Sintering Diagrams. "Acta Metall. 22 131 critical times at which damage tolerance will be lost. With 275-89(1974) knowledge of the activation energies of the sintering mechanisms. " R. M. German,"Fundamentals of Sintering": pp. 260)-69 in Ceramics and the models could be extended to make such predictions for other Glases, Engineered Materials Handtok4ASM Intemational, Materials Park,OH Temperatures. IK. Walton. "The Effective Elastic Moduli of a Random Packing of Spheres,J Design of porous matrixes requires consideration of other Mech. Phyx Solids, 35 [21213-26 (1987 roperties, including shear and interlaminar strength, as well as G. Jefferson.G. K. Haritos, and R. M. Mc Meeking. " The Elastic Response of a Cohesive Aggregate: A Discrete Element Model with Coupled Particle Interaction. mpressive strength. These generally increase as the matrix is Mech. Phys. Solids,50 (12)2539-75(2002) strengthened. As a result. among the mixtures considered in this G. jefferson and R. M. McMeeking, to be published. study, those with higher alumina contents would be preferred. in I B. R Lawn, Fracture of Brittle Solids. and Ed. Cambridge Solid State Science contrast to the mullite-rich mixtures selected based on crack Series. Cambridge University Press, 1993 R. M. German, Particle Packing Characterixtics, Metal Powder deflection considerations. These issues are currently being ederation Princeton. NJ, 1989. aK. L Johnson, Centet Mechanies. Cambridge University Press. 1985