G.N. Morscher et al. Composites Science and Technology 67(2007)1009-1017 Hi-Nicalon fiber [6]. In this study, composites reinforced imens, 4 kN/min for 8 ply specimens, and 10 kN/min for with 2D woven Sylramic-iBN and Hi-Nicalon in a CVi thick specimens. Acoustic emission was monitored during iC matrix were studied. The Syl-iBN composites were var- the tensile test using a Digital Wave Fracture Wave Detec- ied so that the number of tows per length in the two tor. Three wide-band (100 kHz to 2 MHz sensitivity; model orthogonal directions were either the same(balanced) or B1025, Digital Wave, Englewood, CO) sensors were used differed(unbalanced), the latter to simulate enhanced fiber to capture AE activity. Two sensors were placed on the loading in a given direction. The composites reinforced face of the specimen outside of both extensometer knife with Hi-Nicalon in a CVI SiC matrix varied from I to 36 edges whereas the third was placed in the center of the gage plies and differed in constituent content and density section on the opposite face of the extensometer knife edges Only ae data that hit the middle aE sensor first, 2. Experimental i.e., data that occurred in the gage section, were used for the matrix cracking analysis. To determine non-linearity The details on composite processing, constituent con- in the stress-strain curve, a 0.002% offset stress technique tent, and variety of composite panels tested can be found was employed. The 0.002% offset stress is where the linear in Table I [1]. All of the panels consisted of 2D five or eight regression fit curve used to determine elastic modulus, E(5 harness satin woven fabric and were fabricated by ge to <50 MPa)offset by +0.002% intersects with the stress- Power Systems Composites, Newark Delaware. Most pan- strain curve els were either fabricated with BN or carbon interphases After composite failure, some of the specimens were cut Table I also describes the type of tensile specimens, straight and polished along the longitudinal direction in order to sided or dogbone, that were cut from each panel. measure the matrix crack density. The specimens with Tensile testing was performed on an Instron Model 8562 Syl-iBN fibers and a BN-interphase required a plasma (Instron Ltd Canton Mass)universal testing machine. (CF4) etch treatment (500 W for 30 min) in order to reveal The tab ends were enveloped in wire mesh and gripped with the matrix cracks Matrix crack density was measured over pneumatic grips. Clip-on extensometers were used to mea- a 10 mm length along the outer surface of the composite as sure displacement (25 mm gage length). Monotonic or well as within the interior plies. The matrix crack density load-unload-reload hysteresis tests were performed at was determined by counting the number of cracks over that loading and unloading rates of 2 kN /min for the thin spec- distance and dividing by the length Table I pecimen(interphaseINo. specimens Specimen shape f Hi-Nicalon composites standard& ply panels 8 ply (C)121 SHS Dog.A 0.44 8 ply (BND)(21 Dog.B 0.33 8 ply (BN2)(21 2.53 0.31 8 ply (BN3)111 SHS 2.14 0.37 Standard thick panels 30 ply (C)11 Dog.B 8.68 0.34 0.04 0.45 0.17 36 ply(C)(11 sssss 10.56 0.34 0.04 Thin I ply(C)111 Straighte 0.38 0.26 0.04 0.2 2 ply (C) 21 Straight 0.2 0.04 .33 3 ply (C) 21 Straigh 0.9 0.32 0.04 0.35 Iniltrated panels HS(BND)(1 Dog-B 2.45 0.32 0.05 0.25 y-5HS( BN2)1 H Dog-B 2.4 0.32 0.27 BHS(BN)I SHS 2.3 0.33 Sydramic-iBN composites (standard 8 ply panels) 8 ply 7.epcm(1)(11 2.18 0.363 0.377 0.189 8 ply 7.epcm(2)(2 2.17 0.365 .387 0.179 8ply79pcm(3){2} 2.19 0.361 0.443 8 ply 7.epcm(C)111 H 0.229 0.346 0.093 8 ply unbalanced HS Dog.A 0.335 0.069 0.464 0.132 Dogbone tensile mm in length, approximately 15.5 mm in width at grip section and 10.3 mm in width at gage section Dogbone tensile spec c Straight-sided tensile mm边ndm2m1m题tomp03m1wagsHi-Nicalon fiber [6]. In this study, composites reinforced with 2D woven Sylramic-iBN and Hi-Nicalon in a CVI SiC matrix were studied. The Syl-iBN composites were var￾ied so that the number of tows per length in the two orthogonal directions were either the same (balanced) or differed (unbalanced), the latter to simulate enhanced fiber loading in a given direction. The composites reinforced with Hi-Nicalon in a CVI SiC matrix varied from 1 to 36 plies and differed in constituent content and density. 2. Experimental The details on composite processing, constituent con￾tent, and variety of composite panels tested can be found in Table 1 [1]. All of the panels consisted of 2D five or eight harness satin woven fabric and were fabricated by GE Power Systems Composites, Newark Delaware. Most pan￾els were either fabricated with BN or carbon interphases. Table 1 also describes the type of tensile specimens, straight sided or dogbone, that were cut from each panel. Tensile testing was performed on an Instron Model 8562 (Instron Ltd., Canton Mass) universal testing machine. The tab ends were enveloped in wire mesh and gripped with pneumatic grips. Clip-on extensometers were used to mea￾sure displacement (25 mm gage length). Monotonic or load–unload–reload hysteresis tests were performed at loading and unloading rates of 2 kN/min for the thin spec￾imens, 4 kN/min for 8 ply specimens, and 10 kN/min for thick specimens. Acoustic emission was monitored during the tensile test using a Digital Wave Fracture Wave Detec￾tor. Three wide-band (100 kHz to 2 MHz sensitivity; model B1025, Digital Wave, Englewood, CO) sensors were used to capture AE activity. Two sensors were placed on the face of the specimen outside of both extensometer knife edges whereas the third was placed in the center of the gage section on the opposite face of the extensometer knife edges. Only AE data that hit the middle AE sensor first, i.e., data that occurred in the gage section, were used for the matrix cracking analysis. To determine non-linearity in the stress–strain curve, a 0.002% offset stress technique was employed. The 0.002% offset stress is where the linear regression fit curve used to determine elastic modulus, E (5 to 650 MPa) offset by +0.002% intersects with the stress– strain curve. After composite failure, some of the specimens were cut and polished along the longitudinal direction in order to measure the matrix crack density. The specimens with Syl-iBN fibers and a BN-interphase required a plasma (CF4) etch treatment (500 W for 30 min) in order to reveal the matrix cracks. Matrix crack density was measured over a 10 mm length along the outer surface of the composite as well as within the interior plies. The matrix crack density was determined by counting the number of cracks over that distance and dividing by the length. Table 1 Physical properties of composite specimens from Ref. [1] Specimen (interphase) {No. specimens} Weave Specimen shape t, mm ff fi fSiC fp Hi-Nicalon composites Standard 8 ply panels 8 ply (C) {2} 8HS Dog-Aa 2.84 0.28 0.13 0.44 0.15 8 ply (BN1) {2} 5HS Dog-Bb 2.37 0.33 0.05 0.47 0.15 8 ply (BN2) {2} 5HS Dog-B 2.53 0.31 0.06 0.48 0.15 8 ply (BN3) {1} 8HS Dog-A 2.14 0.37 0.05 0.41 0.17 Standard thick panels 30 ply (C) {1} 5HS Dog-B 8.68 0.34 0.04 0.45 0.17 36 ply (C) {1} 5HS Dog-B 10.56 0.34 0.04 0.43 0.19 Thin panels 1 ply (C) {1} 5HS Straightc 0.38 0.26 0.04 0.29 0.41 2 ply (C) {2} 5HS Straight 0.73 0.28 0.04 0.33 0.35 3 ply (C) {2} 5HS Straight 0.92 0.32 0.04 0.35 0.29 Epoxy Iniltrated Panels E8Ply-5HS(BN1) {1} 5HS Dog-B 2.45 0.32 0.05 0.25 0.38 E8Ply-5HS(BN2) {1} 5HS Dog-B 2.45 0.32 0.05 0.27 0.35 E8Ply-8HS(BN) {1} 8HS Dog-B 2.37 0.33 0.05 0.29 0.33 Sylramic-iBN composites (standard 8 ply panels) 8 ply 7.9epcm (1) {1} 5HS Dog-A 2.18 0.363 0.071 0.377 0.189 8 ply 7.9epcm (2) {2} 5HS Dog-A 2.17 0.365 0.069 0.387 0.179 8 ply 7.9epcm (3) {2} 5HS Dog-A 2.19 0.361 0.070 0.443 0.126 8 ply 7.9epcm (C) {1} 5HS Dog-A 2.38 0.332 0.229 0.346 0.093 8 ply unbalanced 5HS Dog-A 2.24 0.335 0.069 0.464 0.132 a Dogbone tensile specimen 203 mm in length, approximately 15.5 mm in width at grip section and 10.3 mm in width at gage section. b Dogbone tensile specimen 152 mm in length, approximately 12.6 mm in width at grip section and 10.3 mm in width at gage section. c Straight-sided tensile specimen 152 mm in length and approximately 12.6 mm in width throughout. 1010 G.N. Morscher et al. / Composites Science and Technology 67 (2007) 1009–1017