3186 Journal of the American Ceramic Society-Morscher et al. VoL. 90. No. 10 Table I. Individual Specimen Properties From Different Composite Panels Thickness, Total fiber Test angle to Panel 2D architecture fraction ( primary fibers (GPa)(MPa) in matrix(MPa) Al 8.7 epcm 0/90, 8 ply, 5HS, single-tow 0.39 261410 7.9 epcm 090.8 ply, 5HS, single-tow A3 3.95 epcm(2)epi 0/90, 8 ply, 5HS, double-tow 2.1 000 50 A4 8.7 epcm 45/45. 8 ply, 5HS, single-tow Bl 0/+67 Braid, 4 layer, tri-axial braid, double-tow Fraction of fibers in the axial direction=0.06. Fraction of fibers in each of the +67"bias directions =0.13 epcm, ends per centimeter: UTS, ultimate tensile strength; with architecture B(panel Bl), consisting of a 2D triaxially was symmetrically located between the two primary fiber direc- braided architecture [0/+67] with balanced fiber content in the tions that contained equal volume fractions +67 bias directions and reduced fiber content in the axial di- Tensile unload-reload hysteresis tests were performed on the rection, was tensile loaded perpendicular to the axial directio dogbone specimens using a universal testing machine(Model (i.e, 23 from the bias fibers). The primary room-temperature 8562: Instron Ltd, Canton, MA) with AE monitoring as de- properties of interest were the elastic modulus, the DFLs as scribed in Morscher.6, 7 A clip-on strain gage(25.4 mm gage, measured by two off-set methods, the UTS, and the matrix- 0.25% strain) was used to measure strain in the gage section. acking behavior as monitored by acoustic emission(AE). Ini Panels Al, A2, A3, and bl were tested in load control at tial implications are discussed for architecture design to model 4 kN/min (- 200 MPa/min depending on composite thickness) and improve the directional cracking strengths of Sic/SiC CMc This loading rate is relatively slow compared with typical mono- components with MI matrices tonic fast-fracture tests and has been determined to be a good ate for ae acquisition A Fracture Wave Detector by Digital Wave Corporation II. Experimental Procedure Englewood, CO) was used to monitor AE waveforms. Three For this study, four panels with architecture A were fabricated wide-band (b1025, Digital Wave Corporation) AE sensors were by cutting 150 mm x 225 mm plies from a 2D-woven 0/90 mounted on the specimens. Two sensors were placed above and Sylramic SiC fabric with a five-harness satin weave and bal below the gage section approximately 50 mm apart from one anced number of tow ends per centimeter(epcm, i.e., the num- another. The third sensor was placed between the other two ber of fiber tows per centimeter in the woven cloth when looking sensors in the middle of the gage section. aE waveforms on all at the weave edge-on)in the 0 and 90 directions. Each single three channels were captured simultaneously when any of the tow consisted of x800 fibers with a 10 um average diameter. three sensors was triggered, i.e., the channels were synchronized For panels Al and A4, the fabric had 8.7 single-tow epcm; but This allowed for easy separation of events. Only events that the plies were cut along the 0 and 90 directions for panel Al triggered the middle sensor were used in the analysis, i.e,onl and at 450 to the orthogonal directions for panel A4. For panels each of the a panels and two specimens from panel B were A2 and a3, the plies were cut along the oand 90 directions; b the fabric had 7.9 single-tow epcm for panel A2, and 3.95 dou tested in this way for this study (see Table D) ble-tow epcm for panel A3. For each A-type panel, eight plies were then stacked and converted to Sylramic-iBN fiber at NASA Glenn. The 2D Sylramic-iBN stacks were then sent to Orthogonal fibers GE Composites, Newark, DE, for MI SiC/SiC processing For panel Bl, the architecture was first formed by creating a four-layer 0/+67 tri-axial braid on a 50-mm-diameter tubular andre. Approximately 23% of the fibers were in the axial di- rection and 77% were in the bias direction at an angle of 67 to the axial fibers. Two as-produced Sylramic fiber tows were Tensile Axis ar architecture was then removed from the mandrel and laid flat to form a 75 mm x -150 mm rectangular preform which was converted to the Sylramic-iBN fibers at NASA and then into a Sic/sic panel with typical Mi processing at GE Tensile 150-mm-long dogbone specimens with a contoured (a gage section(12.7 mm width in grip region and 10 mm width in age region) were machined from each panel. Architecture thickness, and total fiber volume fraction for all tested speci- IS mens from the five panels are listed in Table I. For panels a A2, and A3 specimens, the testing direction was along the pri- nary or 0 direction; but for panel A4, testing was at 45 to the Tensile 0o and 90 directions of the original fabric as shown in Fig. 1(a) Axis For panel B specimens, Fig. I(b) shows that the testing direction was perpendicular to the axial or 0%fiber direction, or along the hoop"direction of the original tubular architecture. Thus, for both off-axis panels of this study, the tensile loading direction Axial Fibers(below surface) FThe Syiramic fibers of this study were originally produced ochester. NH. Both he Sylramic and Syiramic-iBN SiC fibers are currently produced at ATK COI Ceramics, Fig 1. Photographs of composite surface sh ber orientations San Diego. CA and tensile axis for(a)[+45] panel A4 and (b)[0/+67] braid panel Blwith architecture B (panel B1), consisting of a 2D triaxially braided architecture [0/767] with balanced fiber content in the 7671 bias directions and reduced fiber content in the axial di￾rection, was tensile loaded perpendicular to the axial direction (i.e., 231 from the bias fibers). The primary room-temperature properties of interest were the elastic modulus, the DFLS as measured by two off-set methods, the UTS, and the matrix￾cracking behavior as monitored by acoustic emission (AE). Ini￾tial implications are discussed for architecture design to model and improve the directional cracking strengths of SiC/SiC CMC components with MI matrices. II. Experimental Procedure For this study, four panels with architecture A were fabricated by cutting 150 mm
225 mm plies from a 2D-woven 0/90 Sylramic SiC fabricz with a five-harness satin weave and bal￾anced number of tow ends per centimeter (epcm, i.e., the num￾ber of fiber tows per centimeter in the woven cloth when looking at the weave edge-on) in the 01 and 901 directions. Each single tow consisted of B800 fibers with a 10 mm average diameter. For panels A1 and A4, the fabric had 8.7 single-tow epcm; but the plies were cut along the 01 and 901 directions for panel A1 and at 451 to the orthogonal directions for panel A4. For panels A2 and A3, the plies were cut along the 01and 901 directions; but the fabric had 7.9 single-tow epcm for panel A2, and 3.95 dou￾ble-tow epcm for panel A3. For each A-type panel, eight plies were then stacked and converted to Sylramic-iBNz fiber at NASA Glenn.5 The 2D Sylramic-iBN stacks were then sent to GE Composites, Newark, DE, for MI SiC/SiC processing.4 For panel B1, the architecture was first formed by creating a four-layer 0/767 tri-axial braid on a 50-mm-diameter tubular mandrel. Approximately 23% of the fibers were in the axial di￾rection and 77% were in the bias direction at an angle of B671 to the axial fibers. Two as-produced Sylramic fiber tows were combined in the axial and bias directions. A 75 mm-length of the tubular architecture was then removed from the mandrel and laid flat to form a 75 mm
B150 mm rectangular preform, which was converted to the Sylramic-iBN fibers at NASA and then into a SiC/SiC panel with typical MI processing at GE composites. Tensile 150-mm-long dogbone specimens with a contoured gage section (12.7 mm width in grip region and 10 mm width in gage region) were machined from each panel. Architecture, thickness, and total fiber volume fraction for all tested speci￾mens from the five panels are listed in Table I. For panels A1, A2, and A3 specimens, the testing direction was along the pri￾mary or 01 direction; but for panel A4, testing was at 451 to the 01 and 901 directions of the original fabric as shown in Fig. 1(a). For panel B specimens, Fig. 1(b) shows that the testing direction was perpendicular to the axial or 01 fiber direction, or along the ‘‘hoop’’ direction of the original tubular architecture. Thus, for both off-axis panels of this study, the tensile loading direction was symmetrically located between the two primary fiber direc￾tions that contained equal volume fractions. Tensile unload–reload hysteresis tests were performed on the dogbone specimens using a universal testing machine (Model 8562; Instron Ltd., Canton, MA) with AE monitoring as de￾scribed in Morscher.6,7 A clip-on strain gage (25.4 mm gage, 0.25% strain) was used to measure strain in the gage section. Panels A1, A2, A3, and B1 were tested in load control at 4 kN/min (B200 MPa/min depending on composite thickness). This loading rate is relatively slow compared with typical mono￾tonic fast-fracture tests and has been determined to be a good rate for AE acquisition. A Fracture Wave Detector by Digital Wave Corporation (Englewood, CO) was used to monitor AE waveforms. Three wide-band (B1025, Digital Wave Corporation) AE sensors were mounted on the specimens. Two sensors were placed above and below the gage section approximately 50 mm apart from one another. The third sensor was placed between the other two sensors in the middle of the gage section. AE waveforms on all three channels were captured simultaneously when any of the three sensors was triggered, i.e., the channels were synchronized. This allowed for easy separation of events. Only events that triggered the middle sensor were used in the analysis, i.e., only events that occurred in the gage section. One specimen from each of the A panels and two specimens from panel B were tested in this way for this study (see Table I). Table I. Individual Specimen Properties From Different Composite Panels Panel 2D architecture Thickness, mm Total fiber fraction (f) Test angle to primary fibers E (GPa) UTS (MPa) Residual stress in matrix (MPa) A1 8.7 epcm 0/90,8 ply, 5HS, single-tow 2.3 0.39 01 261 410 60 A2 7.9 epcm 0/90, 8 ply, 5HS, single-tow 2.0 0.39 01 250 463 50 A3 3.95 epcm (2) epi 0/90, 8 ply, 5HS, double-tow 2.1 0.39 01 202 444 50 A4 8.7 epcm 45/45,8 ply, 5HS, single-tow 2.4 0.36 451 233 242 40 B1 0/167 Braid, 4 layer, tri-axial braid, double-tow 1.8 0.32w 231 240 338 60 1.8 0.32 231 260 366 60 w Fraction of fibers in the axial direction 5 0.06. Fraction of fibers in each of the 1671 bias directions 5 0.13. epcm, ends per centimeter; UTS, ultimate tensile strength; 2D, two-dimensional. Fig. 1. Photographs of composite surface showing fiber orientations and tensile axis for (a) [745] panel A4 and (b) [0/767] braid panel B1. z The Sylramic fibers of this study were originally produced by Dow Corning, Midland, MI, and were woven into fabric at Albany International Techniweave, Rochester, NH. Both the Sylramic and Sylramic-iBN SiC fibers are currently produced at ATK COI Ceramics, San Diego, CA. 3186 Journal of the American Ceramic Society—Morscher et al. Vol. 90, No. 10