G.N. Morscher et al. Composites Science and Technology 67 (2007)1009-1017 a b uE3OEz 5HS epoxy 8HS epoxy 00 00.10.20.3040.50.60.7080.91 Stress. MPa Strain, d 5.5epcm(1) 5.5 epcm epcm(1) 9.4 epcm(1) 59.4 epcm 9 epcm(3) 03179epcm(1 7.9 epcm (3 9 epcm(1) Stress. MPa Strain.% Fig 3. Acoustic emission activity (normalized cumulative energy) versus composite stress and strain for Hi-Nicalon composites, ()and(b)respective 100μmoo ?, Fig 4. Through-thickness matrix cracks(arrows) in polished 7.95epcm( C) specimen after failure. Note the thick C-interphase. the polished sections of the failed specimens by the normal- shear stress of the fiber-interphase interface [6]. After Refs ized cumulative AE energy results in an estimated matrix [3, 9] the strain behavior of the composite can be modeled crack density that can be used to estimate the interfacial according to the following relationshipthe polished sections of the failed specimens by the normal￾ized cumulative AE energy results in an estimated matrix crack density that can be used to estimate the interfacial shear stress of the fiber-interphase interface [6]. After Refs. [3,9] the strain behavior of the composite can be modeled according to the following relationship: 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 100 200 300 400 Stress, MPa Norm Cum AE Energy 8ply BN1 8ply C 2 ply 3 ply 5HS epoxy 36 ply 30 ply 8HS epoxy 8ply BN2 8ply BN3 1 ply 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Strain, % Norm Cum AE Energy 8ply C 2 ply 3 ply 8HS epoxy 5HS epoxy 36 ply 30 ply 8ply 8ply 8ply BN3 1 ply 8ply 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 0.1 0.2 0.3 0.4 0.5 0.6 Strain, % Norm Cum AE Energy 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 50 100 150 200 250 300 350 400 Stress, MPa Norm Cum AE Energy 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) a b c d Fig. 3. Acoustic emission activity (normalized cumulative energy) versus composite stress and strain for Hi-Nicalon composites, (a) and (b) respectively, and Sylramic-iBN composites, (c) and (d) respectively. Fig. 4. Through-thickness matrix cracks (arrows) in polished 7.95epcm(C) specimen after failure. Note the thick C-interphase. G.N. Morscher et al. / Composites Science and Technology 67 (2007) 1009–1017 1013