G.N. Morscher et al Composites Science and Technology 67(2007)1009-1017 3. Results imen(Table 2). For a balanced weave, f is half the total volume fraction of fibers in the composite(Table 1) 3.1. Stress-strain behavior There were considerable differences in elastic modulus for specimens from different composite panels due to constitu Micrographs of the woven composites are shown in ent content and constituent composition [1]. Some speci Fig 2 of Ref. [1]. The stress-strain curves which were also mens in the same panel also exhibited some variability in presented in Ref [l]are shown here in Fig. 1. Table 2 gives elastic modulus(specimens from 7epcm(2)in Table 2).In some of the important mechanical properties for each ten- general, the specimens with the higher volume fraction of sile specimen. The fiber volume fraction of fibers oriented fibers in the loading direction display higher stresses for in the test direction for each specimen was determined non-linearity in the stress-strain curve. However there were based on the fiber architecture and thickness measurement exceptions, lower elastic modulus composites do have lower used for the tensile test as follows: stresses for non-linearity compared to higherelastic modulus composites of the same architecture(7.epcm specimens in /=Npl NYTRr (epmmo) (1) Table 2). Note also that two of the carbon interphase com- posites, hn 8 ply(C) and Syl-iBN 7epcm(C), have a greater fraction of interphase (Table 1)and consequently where Ply is the number of plies, Nr is the number of fibers lower elastic moduli and 0.002% offset stresses(Table 2) in a tow(800 for Syl-iBN and 500 for Hi-Nicalon), R is the compared to 8 ply composites with lower fractions of average fiber radius (5 um for Syl-iBN and 6.8 um for Hi- interphase. Nicalon), epmmo is tow ends per mm in the O direction, and For some of the specimens, a load-unload-reload hys- f is the thickness measured for the tensile test of each spec- teresis tensile test was performed in order to determine 8 Ply(BN1); E= 258 GPa fo =0.16: 2.5 mm thick Ply: E=221 GP fo = 0.17: 8.6 mm thi 36 Ply: E=217 GPa fo= 0.17; 10.5mm thick f。=0.16; 8 250 10. mm thick E8Ply-8HS; E=118 GP f。=0.17;2.37 mm thick 2 Ply: E= 102 GPa E8Ply-5HS; E= 108 GPa fo=0. 14: 0.76 mm thick f.=0.16: 2.45 mm thick 8 Ply(BN3); E= 225 GPa fo =0.18: 2.35 mm thick 8 Ply(C): E=177 GPa fiber in the =0.14: 2.88 mm thick 0.4 6 Strain. b E=271 GPa CVI; 9. epcm 253GP 4008py(002) 5.5 epcm fo=0.12(002) E=261 GPa Strain. Fig. 1. Stress-strain curves of: (a)HN fiber reinforced and(b) Sylramic-iBN fiber reinforced composites.3. Results 3.1. Stress–strain behavior Micrographs of the woven composites are shown in Fig. 2 of Ref. [1]. The stress–strain curves which were also presented in Ref. [1] are shown here in Fig. 1. Table 2 gives some of the important mechanical properties for each ten￾sile specimen. The fiber volume fraction of fibers oriented in the test direction for each specimen was determined based on the fiber architecture and thickness measurement used for the tensile test as follows: f 0 f ¼ NplyNfpR2 fðepmm0Þ t ð1Þ where Nply is the number of plies, Nf is the number of fibers in a tow (800 for Syl-iBN and 500 for Hi-Nicalon), Rf is the average fiber radius (5 lm for Syl-iBN and 6.8 lm for Hi￾Nicalon), epmm0 is tow ends per mm in the 0 direction, and t is the thickness measured for the tensile test of each spec￾imen (Table 2). For a balanced weave, f 0 f is half the total volume fraction of fibers in the composite (Table 1). There were considerable differences in elastic modulus for specimens from different composite panels due to constitu￾ent content and constituent composition [1]. Some speci￾mens in the same panel also exhibited some variability in elastic modulus (specimens from 7.9epcm(2) in Table 2). In general, the specimens with the higher volume fraction of fibers in the loading direction display higher stresses for non-linearity in the stress–strain curve. However there were exceptions, lower elastic modulus composites do have lower stresses for non-linearity compared to higher elastic modulus composites of the same architecture (7.9epcm specimens in Table 2). Note also that two of the carbon interphase com￾posites, HN 8 ply (C) and Syl-iBN 7.9epcm(C), have a greater fraction of interphase (Table 1) and consequently lower elastic moduli and 0.002% offset stresses (Table 2) compared to 8 ply composites with lower fractions of interphase. For some of the specimens, a load–unload–reload hys￾teresis tensile test was performed in order to determine 0 100 200 300 400 500 600 0 0.1 0.2 0.3 0.4 0.5 0.6 Strain, % Stress, MPa CVI 5.5 epcm fo=0.12 (002) E = 261 GPa CVI; 9.4epcm 8 ply (002) fo=0.21 E=293 GPa CVI 7.9epcm fo=0.18 E=271 GPa E = 253 GPa C-interphase fo = 0.17 E = 230 GPa 0 50 100 150 200 250 300 350 400 450 500 0 0.2 0.4 0.6 0.8 1 Strain, % Stress, MPa 30 Ply; E = 221 GPa fo = 0.17; 8.6 mm thick 36 Ply; E = 217 GPa fo = 0.17; 10.5mm thick 8 Ply (BN3); E = 225 GPa fo = 0.18; 2.35 mm thick 8 Ply (C); E = 177 GPa fo = 0.14; 2.88 mm thick fo refers to the volume fraction of fiber in the loading direction 2 Ply; E = 102 GPa fo = 0.14; 0.76 mm thick 3Ply; E = 114 GPa fo = 0.16; 0.92 mm thick 8 Ply (BN2); E = 244 GPa fo = 0.16; 2.5 mm thick 8 Ply (BN1); E = 258 GPa fo = 0.17; 2.5 mm thick E8Ply-8HS; E = 118 GPa fo = 0.17; 2.37 mm thick E8Ply-5HS; E = 108 GPa fo = 0.16; 2.45 mm thick a b Fig. 1. Stress–strain curves of: (a) HN fiber reinforced and (b) Sylramic-iBN fiber reinforced composites. G.N. Morscher et al. / Composites Science and Technology 67 (2007) 1009–1017 1011