Journal of the American Ceramic Sociery-acobsen and Brondsted Vol. 84. No. 5 Table L. Elastic Properties and Characteristic Stresses of the Materials (GPa) (GPa) vn,=v, v (GPa) (GPa)(X10-6K-)(X10-6K-)(MPa)(MiPa)(MPa)(MPa) SiC/SiC Calculated 1550.200.1 0.220.14 Compression 1700.260.20 C/SiC Calculated 1460.210.0828 111117 Tension Compression 110.1400.230.08 lated properties are shown in the first line, mea erties in the second ticients of thermal he initial slope and the slope at the sure stress(c )of the stress-strain curve, respec lso see Fig. 6). Measured by the manufacturer, Sygulla et al. Table Il. Strength Properties of Sic/SiC and C/sic (o)=18s-045)eakm)04555082 IPa 3230.681760.60 For a/s > 0.82, the crack density in the 90 bundles remained 0.32 0.82 -521-0.42 constant at(Loo)=7 cracks/mm (B) C/SiC: The as-received material contained tunneling matrix cracks in the 90 bundle and some delamination between the 0o and 90o bundles. a few transverse matrix cracks were al crack density in the 0o bundles as a function of peak stress was observed in the 0 bundles. Replicas taken during the unload fitted using the following expression eloading procedure revealed no further damage. After fracture, a piece of material lying outside the replicated region was embedded (a=31(-045)cracks/mm) az045 (1) in epoxy, polished, and investigated using optical microscopy Similar to the 90 bundles, the crack density (Loo) is given by ξ-100十acsc e-200 -500 -600 10 0.6-05-04-03-0.2-0100.10.2 Fig 8. Fracture surface of C/SiC showing a high crack density and small particles on the fibers that may be responsible for very high friction Strain(%) between fiber and matrix, leading to high local crack densities Fig. 6. Compressive stress-strain behavior of SiC/SiC and C/SiC. 39100m V Smooth SiC-fiber VV SiC-matrix AC-interphase Fig 9. Fracture surface of SiC/SiC showing carbon interphase sticking to Fig. 7. Fracture surface of SiC/SiC showing tunneling cracks the Sic fiber and sawtooth failure of the interphasecrack density in the 0° bundles as a function of peak stress was fitted using the following expression: ~L0! 21 5 31.6S s S 2 0.45D ~cracks/mm! s S $ 0.45 (1) Similar to the 90° bundles, the crack density (L90) 21 is given by ~L90! 21 5 18.9S s S 2 0.45D ~cracks/mm! 0.45 # s S # 0.82 (2) For a/S . 0.82, the crack density in the 90° bundles remained constant at (L90) 21 5 7 cracks/mm. (B) C/SiC: The as-received material contained tunneling matrix cracks in the 90° bundle and some delamination between the 0° and 90° bundles. A few transverse matrix cracks were also observed in the 0° bundles. Replicas taken during the unloading/ reloading procedure revealed no further damage. After fracture, a piece of material lying outside the replicated region was embedded in epoxy, polished, and investigated using optical microscopy. Fig. 6. Compressive stress–strain behavior of SiC/SiC and C/SiC. Fig. 7. Fracture surface of SiC/SiC showing tunneling cracks. Fig. 8. Fracture surface of C/SiC showing a high crack density and small particles on the fibers that may be responsible for very high friction between fiber and matrix, leading to high local crack densities. Fig. 9. Fracture surface of SiC/SiC showing carbon interphase sticking to the SiC fiber and sawtooth failure of the interphase. Table I. Elastic Properties and Characteristic Stresses of the Materials† Ex (GPa) Ey 5 Ez (GPa) nxy 5 nxz nyz Gxy 5 Gxz (GPa) Gyz (GPa) ax (31026 K21 ) ay 5 az (31026 K21 ) smc (MPa) tmc (MPa) sR (MPa) sr R (MPa) SiC/SiC Calculated 124 155 0.20 0.16 56 60 4.2 3.7 14 26 Tension 147 0.22 0.14 60 4‡ 4‡ 41 48 Compression 170 0.26 0.20 C/SiC Calculated 56 146 0.21 0.08 28 37 4.5 1.7 111 117 Tension 113 0.16 0.04 40 5‡ 3‡ 0 44 Compression 110,140 0.23 0.08 † Calculated properties are shown in the first line, measured tensile properties in the second line along with shear properties and coefficients of thermal expansion, and compressive properties in the third line for each of the materials. Two values for the compressive stiffness along the y- or z-direction denote the initial slope and the slope at the crack closure stress (scl) of the stress–strain curve, respectively (also see Fig. 6). ‡ Measured by the manufacturer, Sygulla et al. Table II. Strength Properties of SiC/SiC and C/SiC S (MPa) εS (%) T (MPa) gT (%) Scom (MPa) εcom (%) SiC/SiC 323 0.68 176 0.60 2632 20.39 C/SiC 200 0.32 150 0.82 2521 20.42 1046 Journal of the American Ceramic Society—Jacobsen and Brøndsted Vol. 84, No. 5