G.N. Morscher et al. Composites Science and Technology 67 (2007)1009-1017 8 ply BN2- S 0. 88 ply BN1 8 ply C 3 Ply 山莓 2 Ply 8HS epoxy 30 ply 0+ Stress on Load-Bearing CVI SiC, MPa 5.5 epcm (1) o000oo 0.9 5.5epcm(2) 7.9 epcm(1) 079.4epm(2 C-interphase 0.5 -7. 9 epcm(2) 9. 4 epcm (1) 0.2 7.9 epcm (3) 00 60 Stress on Load-Bearing CVI SiC, MPa Fig. 6. Normalized AE energy versus stress on load-bearing CVI SiC for: (a) Hi-Nicalon and (b) Sylramic-iBN composites. Arrows espond to the onset stresses for matrix cracking of the two different matrix cracking materials. Large circles correspond to the simple Weibull model the three matrix cracking distributions. ted are data from single tow minicomposites [10, 11] which also correlate well with the low-density woven composites 目EE巴品四 8HS by the 00 minicomposites [1] for these low-density woven 8 CVI SiC composites the"stress on the load-bearing SiC"(Fig. 6), even though 3423 4. discussion An excellent correlation exists for matrix cracking of the higher volume fraction oriented composite specimens with BN3 the stress-strain behavior(Fig. 2), the stress-dependent AE 0 behavior(Fig. 3), and interfacial shear stress for the differ 001200 ent C-interphase and BN-interphase composites are signif- Stress on Load-Bearing CVI SiC, MPa icantly different. The two Syl-iBN unbalanced composite Fig. 7. Estimated matrix crack density for Hi-Nicalon, CVI SiC matrix specimens oriented in the lower fiber volume fraction diree composites.ted are data from single tow minicomposites [10,11] which also correlate well with the low-density woven composites and further demonstrates that the load is primarily carried by the 0 minicomposites [1] for these low-density woven CVI SiC composites. 4. Discussion An excellent correlation exists for matrix cracking of the higher volume fraction oriented composite specimens with the ‘‘stress on the load-bearing SiC’’ (Fig. 6), even though the stress–strain behavior (Fig. 2), the stress-dependent AE behavior (Fig. 3), and interfacial shear stress for the differ￾ent C-interphase and BN-interphase composites are signif￾icantly different. The two Syl-iBN unbalanced composite specimens oriented in the lower fiber volume fraction direc- 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 100 200 300 400 500 600 Stress on Load-Bearing CVI SiC, MPa Norm Cum AE 5.5 epcm (1) 5.5 epcm (2) C-interphase 7.9 epcm 7.9 epcm (1) 7.9 epcm (2) 7.9 epcm (3) 9.4 epcm (1) 9.4 epcm (2) 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 500 1000 1500 Stress on Load-Bearing CVI SiC, MPa Normalized Cumulative AE Energy 8 ply BN1 30 ply 36 ply 8 ply BN2 8 ply C 8 ply BN3 1 Ply 2 Ply 8HS epoxy 3 Ply a b Fig. 6. Normalized AE energy versus stress on load-bearing CVI SiC for: (a) Hi-Nicalon and (b) Sylramic-iBN composites. Arrows on abscissa correspond to the onset stresses for matrix cracking of the two different matrix cracking materials. Large circles correspond to the simple Weibull models for the three matrix cracking distributions. 0 2 4 6 8 10 12 0 200 400 600 800 1000 1200 1400 Stress on Load-Bearing CVI SiC, MPa Estimated Crack Denisty, mm-1 3ply 1ply 2ply single tow minicomposite (C) 8ply C 8ply BN3 8ply BN3 8ply BN2 30ply 8ply BN1 36ply 8HS epoxy single tow minicomposite (BN) Fig. 7. Estimated matrix crack density for Hi-Nicalon, CVI SiC matrix composites. G.N. Morscher et al. / Composites Science and Technology 67 (2007) 1009–1017 1015