wwceramics. org/ACT Infuence of Interface Characteristics on the Mechanical Properties The present paper compares SiC/SiC minicompos- Table il. Main Fibers and Tow Characteristics ites reinforced with Hi-NicalonS and SA3 fibers, with the primary emphasis on the correlation between me- chanical behavior and fiber/matrix interface characteris Fibers NicalonS SA3 tics. Minicomposites are unidirectional test specimens Density (g/cm) 2.98(2.94)3.1(2.95) reinforced by a single tow. The minicomposite approach Number of fibers ivestigation ha Average diameter(ur 13 7(699) dressed in several papers.7-9 Interface characteristics Specific mass(g/1000 m) 193(191)190(192) can be extracted from features of tensile stress-strain Young's modulus(GPa) 372(375)387(385) behavior Thermal conductivity Tows ntal Procedure Strain to failure(%) 0.73(0.02)0.68(0.04) Failure stress(MPa) 2477(75)2412(122) Material Manufacture standard dev pions fo are fiber properties measured in-house ow characteristics measured in-house. SiC/SiC minicomposites were manufactured using the CVI method. Hi-NicalonS(Nippon Carbon Co. Tensile Tests Ltd, Takauchi, Japan) or Tyranno SA3(UBE Indus- tries, Tokyo, Japan) tows were used as reinforcement Uniaxial tensile tests were performed at room tem- (Table D). The tows were coated by: perature at a constant strain rate(50 um/min). The load either a single layer of pyrocarbon(PyC): thick- was measured using a 500N load cell.Minicomposite ness=150 nm deformations were measured using two-parallel linear- or a multilayer containing five layers of Pyc variable differential transformer(LVDT)extensometers alternating with SiC: each layer was 30 nm thick. that were attached to the grips. Extensometers were lo- The thickness of the PyC layer on the fiber was cated on opposite sides of specimens, in order to ensure ignment of grips were a A 40-50% fiber volume fraction was designed. tubes using glue. The tubes were gripped into the testing Fractions of fibers and matrix within minicomposites machine Gauge length(distance between the inner ends were determined using image analysis of micrographs of of the tubes)was 25 mm. The gripping system compli- polished cross-sections(Table I1). The main fiber and ance is needed to take account of load train deforma- tow characteristics are summarized in Table Il. Note tion. For compliance calibration purpose, deformations that Hi-NicalonS and SA3 exhibit comparable mechan- of a few specimens were also measured using a digital image correlation technique. This technique is based on Table I. Characteristics of SiC/SiC Minicomposites(e= thickness of the PyC layers Name Fiber Interphase(s) thickness Section (mm) V(%) Single layer ex 150 nm e layer e 150 nm 43 Multilayer(x5)el=22=23=e4~ nm 0.140 e5~150nm M4 SA3 Multilayer(x5)el=22=63=e4- M5 HiS Multilayer(×5)el=c2=e3=姓 0.145 e5-150nm M6 His Single layer e 30 nmThe present paper compares SiC/SiC minicompos￾ites reinforced with Hi-NicalonS and SA3 fibers, with the primary emphasis on the correlation between me￾chanical behavior and fiber/matrix interface characteris￾tics. Minicomposites are unidirectional test specimens reinforced by a single tow. The minicomposite approach to composite design and investigation has been ad￾dressed in several papers.17–19 Interface characteristics can be extracted from features of tensile stress–strain behavior.17–19 Experimental Procedure Material Manufacture SiC/SiC minicomposites were manufactured using the CVI method. Hi-NicalonS (Nippon Carbon Co. Ltd., Takauchi, Japan) or Tyranno SA3 (UBE Indus￾tries, Tokyo, Japan) tows were used as reinforcement (Table I). The tows were coated by: either a single layer of pyrocarbon (PyC): thick￾ness 5 150 nm, or a multilayer containing five layers of PyC alternating with SiC: each layer was 30 nm thick. The thickness of the PyC layer on the fiber was 30 nm. A 40–50% fiber volume fraction was designed. Fractions of fibers and matrix within minicomposites were determined using image analysis of micrographs of polished cross-sections (Table II). The main fiber and tow characteristics are summarized in Table II. Note that Hi-NicalonS and SA3 exhibit comparable mechan￾ical properties. Tensile Tests Uniaxial tensile tests were performed at room tem￾perature at a constant strain rate (50 mm/min). The load was measured using a 500 N load cell. Minicomposite deformations were measured using two-parallel linear￾variable differential transformer (LVDT) extensometers that were attached to the grips. Extensometers were lo￾cated on opposite sides of specimens, in order to ensure alignment of grips. Minicomposite ends were affixed within metallic tubes using glue. The tubes were gripped into the testing machine. Gauge length (distance between the inner ends of the tubes) was 25 mm. The gripping system compli￾ance is needed to take account of load train deforma￾tion. For compliance calibration purpose, deformations of a few specimens were also measured using a digital image correlation technique. This technique is based on Table I. Characteristics of SiC/SiC Minicomposites (e 5 thickness of the PyC layers) Name Fiber Interphase(s) thickness Section (mm2 ) Vf (%) M1 HiS Single layer eB150 nm 0.140 46 M2 SA3 Single layer eB150 nm 0.150 43 M3 HiS Multilayer (  5) e1 5 e2 5 e3 5 e4B30 nm 0.140 46 e5B150 nm M4 SA3 Multilayer (  5) e1 5 e2 5 e3 5 e4B30 nm 0.150 43 e5B150 nm M5 HiS Multilayer (  5) e1 5 e2 5 e3 5 e4B30 nm 0.145 44 e5–150 nm M6 HiS Single layer eB30 nm 0.160 40 Table II. Main Fibers and Tow Characteristics Fibers Hi￾NicalonS SA3 Density (g/cm3 ) 2.98 (2.94) 3.1 (2.95) Number of fibers 500 1600 Average diameter (mm) 13 7 (6.99) Specific mass (g/1000 m) 193 (191) 190 (192) Young’s modulus (GPa) 372 (375) 387 (385) Thermal conductivity (W m1 K1 ) 18 65 Tows Strain to failure (%) 0.73 (0.02) 0.68 (0.04) Failure stress (MPa) 2477 (75) 2412 (122) Data within parentheses are fiber properties measured in-house or standard deviations for tow characteristics measured in-house. www.ceramics.org/ACT Influence of Interface Characteristics on the Mechanical Properties 293