Interface Design for Oxidation-Resistant Ceramic Composite 1.3 1,2,57.5,1010°C 0.9 A(GPa) 1.2t/R<6% 0.8 口20(BN 0.7 1.1 V150 0.6 000 521 0.5 t<0.5_m:EE 005 04 00.2040.60.8 1.2 -0.1-0.0500.050.10.1502025 R{(Ect1)1+0y}tR}{aa)-1}1+0.EE (b) Fig. 8. Universal plots can be used to obtain the models that use transversely isotropic moduli and C of (a) effective modulus and (b) effective cte in the i Plots are a good approximation for up to 0.5 um thi ting on an 8 um fiber radius (R). Symbols E and c refer ubscripts t, c, and f stand for the transverse, coatit in the original reference, where the matrix on the side pectively. Asterisk ()denotes effective properties. (Plot(b)was in Eq (8)should be inverted gauge length of bridging fibers resulting from short debond isotropic coating--it can be as high as 0.7 for an elastic anisotropy that are, in turn, a consequence of high T. As discussed of 6)from the He and Hutchinson. o analysis is not satisfied. matrix cracks in high-strength material deflect into even in the coating. A similar discrepancy has been noted for interfacial cracks, rather than a single debond. Therefore, crack deflection criteria using a laminate geometry. Although this deflection for this CMC is decided primarily by fracture anisotropy result is not well understood, it is encouraging with regard to the within the coating, rather than at the coating/fiber or coating development of alternative coatings in that the fracture energies matrix interface. Unusual fiber pushout load-deflection curves and the sliding friction may not be ired to be as low as suggest substantial effects of rough interfaces, and subsequent reviously thought. In any event, many of the coating approaches analysis implies that the critical strain energy to propagate cracks discussed later are likely to exhibit sufficiently high fracture in this interfacial region may be as high as 25 J/m". This is more energy and friction to greatly restrict debond lengths. It is helpful than half the fracture energy across the strongest graphite planes. to know that, although the composites discussed above exhibit The criterion of fracture energy anisotropy of -1/4 or less(for an matrix crack spacings of from one to three fiber diameters 0 0.4 LONGITUDINAL TENSILE STRAIN (%) rain behaviors in tension measured on the two-dimensional Si abricated from (I untreated or () treated nical amic grade) fibers. Complex crack deflection within the coating on treated fibers(schematic upper left) leads to higher friction than smooth interfacial