May 2001 Mechanical Properties of Two Plain-Woven Cvl SiC-Matrix Composites 1045 SiC/SIC SImubation be苏 0.5 (b) Composite Strain, E(%) Fig 3. (a) Experimental stress-strain behavior of SiC/SiC Crack closure occurs below 20 MPa(insert).(b) Simulated stress-strain behavior of SiC/SiC Permanent strains are smaller than the ones obtained experimentally. (o/o,=0.86, or- 26 MPa, and T=80 MPa. 250 C/sic Experim Simulation 435 GPa 200+tL,=4.5MPamm 150 十士叶 HHHHH 0000.050.100.150.200.250300.35 0050.100150200.25030035 Composite Strain, e( (b) 4.(a) Experimentally observed stress-strain behavior of C/Sic (b) Simulated stress-strain behavior of C/SiC with TLo =4.5 MPa mm and oT=240 8150 specimen tailed before 9as 0.8 Engineering Shear Strain, 'y(%) Engineering Shear Strain, %y(%) Fig. 5. Shear stress-strain behavior of (a) SiC/SiC and(b)C/SiC, with periodic unloading/reloading. 90 bundles. No saturation of matrix cracking was observed in the The tunneling crack density (Loo) in the 90 bundles was 0° bundles estimated by counting the number of cracks within a bundle and Delamination crack growth was caused by crack bra anching dividing this number by the bundle width Only tunneling cracks from a 90 tunneling matrix crack. The tunneling matrix crack spanning the bundle height were included, and the small, porosi the 90 bundle had a curly pattern and ran preferably around the induced cracks in the matrix-rich regions were not included, fiber or through the interphase. A similar behavior has been because they branched in various directions observed in a SiC/CAS cross-ply laminate. Except for delani- Matrix cracks and, consequently, the matrix crack spacing in the nation behavior, the above-described behavior for SiC/SiC was 0 bundles (Lo)occurred only in cross sections where the bundles onsistent with observations by several investigators. 4 26,28-31,34 were cut at the tapered end. In the middle of the bundles, the The delamination may have been due to an edge effect or fiber-packing arrangement was too dense to show transverse processing problems related to the thickness of the composit matrix cracks, if any existed. The matrix-cracking densities varied tested(difficulties in infiltrating a thick laminate) linearly with stress. The ex ntally observed evolution of90° bundles. No saturation of matrix cracking was observed in the 0° bundles. Delamination crack growth was caused by crack branching from a 90° tunneling matrix crack. The tunneling matrix crack in the 90° bundle had a curly pattern and ran preferably around the fiber or through the interphase. A similar behavior has been observed in a SiC/CAS cross-ply laminate.13 Except for delami￾nation behavior, the above-described behavior for SiC/SiC was consistent with observations by several investigators.24,26,28–31,34 The delamination may have been due to an edge effect or processing problems related to the thickness of the composite tested (difficulties in infiltrating a thick laminate). The tunneling crack density (L90) 21 in the 90° bundles was estimated by counting the number of cracks within a bundle and dividing this number by the bundle width. Only tunneling cracks spanning the bundle height were included, and the small, porosity￾induced cracks in the matrix-rich regions were not included, because they branched in various directions. Matrix cracks and, consequently, the matrix crack spacing in the 0° bundles (L0) occurred only in cross sections where the bundles were cut at the tapered end. In the middle of the bundles, the fiber-packing arrangement was too dense to show transverse matrix cracks, if any existed. The matrix-cracking densities varied linearly with stress. The experimentally observed evolution of Fig. 4. (a) Experimentally observed stress–strain behavior of C/SiC (b) Simulated stress–strain behavior of C/SiC with tL0 5 4.5 MPazmm and sT 5 240 MPa. Fig. 5. Shear stress–strain behavior of (a) SiC/SiC and (b) C/SiC, with periodic unloading/reloading. Fig. 3. (a) Experimental stress–strain behavior of SiC/SiC. Crack closure occurs below 20 MPa (insert). (b) Simulated stress–strain behavior of SiC/SiC. Permanent strains are smaller than the ones obtained experimentally. (si /sp 5 0.86, sT 5 26 MPa, and t 5 80 MPa.) May 2001 Mechanical Properties of Two Plain-Woven CVI SiC-Matrix Composites 1045