Availableonlineatwww.sciencedirect.com DIRECT E噩≈3S SEVIER Journal of the European Ceramic Society 25(2005)599-604 www.elsevier.com/locate/jeurceramsoc Distribution of fibre pullout length and interface shear strength within a single fibre bundle for an orthogonal 3-D woven Si-Ti-C-O fibre/Si-Ti-C-O matrix composite tested at 1100C in air lan J Davies a, * Toshio Ogasawara", Takashi Ishikawa a Dero /dvanced Composite Evaluation Technology Center, Institute of Space Technology and eronautics tralia a department of Mechanical Engineering, Curtin University of Technology. G PO. Box U1987, Perth, WA 6845, Australia Japan Aerospace Exploration Agency (JAXA), 6-13-1 Ohsawa, Mitaka-Shi, Tokyo 181-0015, Japan Received 16 December 2003; received in revised form 10 March 2004; accepted 21 March 2004 Available online 15 June 2004 Abstract The distributions of fibre strength, pullout length, and fibre/matrix interface shear strength within a single fibre bundle were investigated for a 3-D woven SiC/SiC composite tensile tested at 1100C in air. Fibre pullout lengths were largest at the fibre bundle centre with an embrittled region of approximate width 15 um at the perimeter. Whereas the fibre strength varied by less than a factor of 2 across the fibre bundle, the fibre/matrix interface shear strength varied by a factor of -23 with a minimum100= 16 MPa) at the centre and a maximum(. 25+0. 21 GPa) close to the embrittled region. The minimum fibre/matrix interface shear strength required for the transition between pseudo-ductile and brittle behaviour was thus estimated to be 2. 25+0.21 GPa for this composite system C 2004 Elsevier Ltd. All rights reserved Keywords: Composites; Failure analysis; Fibres; Interfaces; SIC/SiC 1. Introduction may increase t to such an extent that crack deflection mech anisms at the fibre/matrix interface are suppressed, + lead The mechanical properties of ceramic matrix composites ing to the formation of an embrittled region characterised by (CMCs)are known to be greatly influenced by the fibre flat fibre fracture surfaces and negligible pullout lengths.3. strength Weibull parameters, So and m, measured in situ A related concern for CMCs containing fibres based on the the composite together with the fibre/matrix interface shear silicon carbide(SiC) system is the formation of an oxide strength, tI Whilst the largest values of tensile strength, o, film at the fibre surface, 5 which acts as a flaw population for CMCs have generally been achieved using low values of and decreases fibre strength. 6 T(typically <10 MPa)with subsequently large fibre pull- Modelling of the oxidation behaviour in cmcs based out lengths on the order of several hundred microns, recent on the SiC/Sic system has indicated the maximum ox work has shown t values of 370 MPa to also be consistent idation rate to occur at intermediate temperatures (e.g with superior mechanical properties. An essential aspect of 500-900C) with the rate decreasing at higher temper high strength CMCs is their use of fibre/matrix interfaces atures (e.g. >1100c)due to sealing of cracks at the based on weakly bonded materials such as pyrolytic carbon specimen surface; 18, 19 oxidation resistance was also found (py-C), boron nitride(BN), 6 and La-monazite(LaPO4).7 to increase with use of thin(<0. 1 um) py-C interfaces 18 However, the extreme oxygen sensitivity of py-C and BN Although several researchers have experimentally in above 500C is a major cause for concern in CMCs that typ- vestigated the effects of oxidation on SiC/SiC composites ically exhibit low-stress matrix microcracking.Oxidation 220-24 and bn2- terraces. in addition of the fibre/matrix interface and exposed fibre surfaces0-13 to other CMCs containing SiC fibres, 8 relatively little data is available for the values of So, m, and t within partially oxidised CMCs, particularly for the variation of these prop- E-mail address: 1.Davies(@curtin.edu. au(IJ. Davies) erties within individual fibre bundles. Such informationJournal of the European Ceramic Society 25 (2005) 599–604 Distribution of fibre pullout length and interface shear strength within a single fibre bundle for an orthogonal 3-D woven Si–Ti–C–O fibre/Si–Ti–C–O matrix composite tested at 1100 ◦C in air Ian J. Davies a,∗, Toshio Ogasawara b, Takashi Ishikawa b a Department of Mechanical Engineering, Curtin University of Technology, G.P.O. Box U1987, Perth, WA 6845, Australia b Advanced Composite Evaluation Technology Center, Institute of Space Technology and Aeronautics (ISTA), Japan Aerospace Exploration Agency (JAXA), 6-13-1 Ohsawa, Mitaka-Shi, Tokyo 181-0015, Japan Received 16 December 2003; received in revised form 10 March 2004; accepted 21 March 2004 Available online 15 June 2004 Abstract The distributions of fibre strength, pullout length, and fibre/matrix interface shear strength within a single fibre bundle were investigated for a 3-D woven SiC/SiC composite tensile tested at 1100 ◦C in air. Fibre pullout lengths were largest at the fibre bundle centre with an embrittled region of approximate width 15
m at the perimeter. Whereas the fibre strength varied by less than a factor of 2 across the fibre bundle, the fibre/matrix interface shear strength varied by a factor of ∼23 with a minimum (100±16 MPa) at the centre and a maximum (2.25±0.21 GPa) close to the embrittled region. The minimum fibre/matrix interface shear strength required for the transition between pseudo-ductile and brittle behaviour was thus estimated to be 2.25 ± 0.21 GPa for this composite system. © 2004 Elsevier Ltd. All rights reserved. Keywords: Composites; Failure analysis; Fibres; Interfaces; SiC/SiC 1. Introduction The mechanical properties of ceramic matrix composites (CMCs) are known to be greatly influenced by the fibre strength Weibull parameters, So and m, measured in situ the composite together with the fibre/matrix interface shear strength, τ. 1 Whilst the largest values of tensile strength, σ, for CMCs have generally been achieved using low values of τ (typically <10 MPa2) with subsequently large fibre pull￾out lengths on the order of several hundred microns,3 recent work has shown τ values of 370 MPa to also be consistent with superior mechanical properties.4 An essential aspect of high strength CMCs is their use of fibre/matrix interfaces based on weakly bonded materials such as pyrolytic carbon (py-C),5 boron nitride (BN),6 and La-monazite (LaPO4).7 However, the extreme oxygen sensitivity of py-C and BN above 500 ◦C is a major cause for concern in CMCs that typ￾ically exhibit low-stress matrix microcracking.8 Oxidation of the fibre/matrix interface9 and exposed fibre surfaces10–13 ∗ Corresponding author. E-mail address: I.Davies@curtin.edu.au (I.J. Davies). may increase τ to such an extent that crack deflection mech￾anisms at the fibre/matrix interface are suppressed,14 lead￾ing to the formation of an embrittled region characterised by flat fibre fracture surfaces and negligible pullout lengths.3,15 A related concern for CMCs containing fibres based on the silicon carbide (SiC) system is the formation of an oxide film at the fibre surface,15 which acts as a flaw population and decreases fibre strength.16 Modelling of the oxidation behaviour in CMCs based on the SiC/SiC system has indicated the maximum ox￾idation rate to occur at intermediate temperatures (e.g. 500–900 ◦C17) with the rate decreasing at higher temper￾atures (e.g. ≥1100 ◦C18) due to sealing of cracks at the specimen surface;18,19 oxidation resistance was also found to increase with use of thin (≤0.1
m) py-C interfaces.18 Although several researchers have experimentally in￾vestigated the effects of oxidation on SiC/SiC composites containing py-C2,20–24 and BN25–27 interfaces, in addition to other CMCs containing SiC fibres,28 relatively little data is available for the values of So, m, and τ within partially oxidised CMCs, particularly for the variation of these prop￾erties within individual fibre bundles. Such information 0955-2219/$ – see front matter © 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.jeurceramsoc.2004.03.022