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Abstracts (International Journals and Books)

[10]   I. J. Davies and R. D. Rawlings, “Mechanical properties in compression of CVI-densified porous carbon-carbon composites”, Composites Sci. Technol., 59(1) pp. 97-104 (1999).

Abstract: Compressive properties of a porous 2-D planar-random carbon-carbon (c-c) composite preform densified using chemical vapour infiltration (CVI) of pyrolytic carbon were evaluated and compared to those of previously reported c-c composites densified using a non-CVI technique. Stress-strain curves and failure modes of CVI composites were similar to those seen in non-CVI porous c-c composites. For equivalent-density composites the CVI technique achieved improved in-plane compressive properties but inferior out-of-plane properties when compared to the non-CVI case. Compressive property anisotropy ratios of CVI composites decreased slightly from that of the uninfiltrated preform whilst comparison of compressive properties with previously determined flexural properties for CVI composites showed general agreement. A previously developed microstructural model of the composite was used to explain the results.

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[9]   I. J. Davies, T. Ishikawa, N. Suzuki, M. Shibuya, T. Hirokawa, and J. Gotoh, “Tensile and in situ fibre properties of 3-D SiC/SiC-based composite tested at elevated temperature in vacuum and air with and without an oxidation protection system”, Ceram. Eng. Sci. Proc., 19(3) pp. 275-280 (1998).

Abstract: In this study, a 3-D woven SiC/SiC-based composite was manufactured with and without an oxidation protection glass-based sealant and tested in tension up to 1380 ^oC in vacuum and air. Stress/strain curves showed sealed specimens tested in air to have similar mechanical properties to those of unsealed specimens tested in vacuum at elevated temperature (400 MPa strength and 1.2% strain to failure at 1200 ^oC) and significantly improved compared to unsealed specimens tested in air. Creep testing of the sealed composite at 1100 ^oC and 1200 ^oC in air indicated lifetimes significantly greater than those achieved for previous materials. In a similar manner, in situ fibre strength Weibull parameters and fibre/matrix interface shear strength were found to be essentially similar for sealed specimens tested in air and unsealed specimens tested in vacuum. Overall, these results indicated the oxidation protection system utilised to be extremely effective for short- and medium-term exposure up to at least 1200 ^oC in air.

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[8]   T. Ishikawa, N. Suzuki, I. J. Davies, M. Shibuya, T. Hirokawa, and J. Gotoh, “Creep behavior and modeling of SiC-based PC ceramic matrix composites with glass sealant in high temperature air”, Key Eng. Maters., 164/165, pp. 197-200 (1998).

Abstract: NAL, Ube Industries Ltd., and Shikibo Ltd. have been conducting a joint R&D effort of several types of ceramic matrix composites (CMC) using Si-Ti-C-O (Tyranno^®) fiber and 3-D fabric reinforcement. The present report focuses on a CMC using polymer impregnation and pyrolysis (PIP) matrix. The final point of improvement is a glassy sealant technology for better oxidation resistance developed by Kawasaki Heavy Industries (KHI) Ltd. By applying this sealant, static strengths in high temperature air up to 1200 ^oC were improved to be 90% of high temperature strengths in vacuum. Creep tests were also conducted and it was found that this CMC system with the sealant exhibits superb creep rupture time, 700 hours (4 weeks) at 140 MPa and 200 hours at 180 MPa in 1100 ^oC air, which is more than a doubled strength of the forerunner CVI-CMC. The indicated strength vs creep time relationship demonstrates a superiority of the present material in a creep behavior. Creep strain rates were also measured for many specimens. An attempt was made for deduction of creep constitutive equations based on constitutive materials properties.

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[7]   I. J. Davies, T. Ishikawa, M. Shibuya, T. Hirokawa, and J. Gotoh, “In Situ properties of 3-D woven SiC/SiC-based composite”, Key Eng. Maters., 164/165, pp. 201-204 (1998).

Abstract: In situ properties (Weibull fibre strength parameters, S_o and m, fibre pull-out length distribution, and interfacial shear strength, t) were determined for a 3-D woven SiC/SiC-based composite after tensile testing up to 1380 ^oC in air and vacuum - selected specimens had been impregnated with a proprietary glass sealant prior to mechanical testing. Unsealed specimens tested in vacuum and sealed specimens tested in air possessed in situ properties consistent with excellent tensile properties previously observed, i.e., S_o>3 GPa, 4<m<7, t<10 MPa, and >400 mm average fibre pull-out length. In contrast to this, in situ properties for unsealed specimens tested in air (1100 ^oC and 1200 ^oC) suggested poor macroscopic mechanical properties, i.e., S_o<1.5 GPa, 2<m<3, t>50 MPa, and <100 mm average fibre pull-out length, as was indeed the case. Results were explained in terms of the fibre/matrix interface and oxidation protection ability of the glass sealant.

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[6]   I. J. Davies, A. Nozue, S. Nakabayashi, and T. Okubo, “Fracture behaviour of boride-dispersed composites fabricated by hot-pressing amorphous Ni₆₀Mo₃₀B₁₀ powder”, J. Maters. Sci., 33(19) pp. 4727-4732 (1998).

Abstract: Microstructural and mechanical property characteristics were investigated for three boride-dispersed composites fabricated by hot-pressing amorphous Ni₆₀Mo₃₀B₁₀ powder. The first composite was tested in the as-hot-pressed condition (“HP”) whilst the other specimens were subjected to a solution treatment (“ST”) and further aging (“STA”). X-ray diffraction showed the HP and ST composites to consist of Mo₂NiB₂ particles in a Ni-rich matrix whilst the STA material contained Mo₂NiB₂ particles in a Ni₃Mo matrix. The hardness and fracture toughness decreased and increased, respectively, for the ST material compared to the HP case whilst the STA case showed increased and decreased hardness and fracture toughness, respectively, compared to the ST composite. These results were explained in terms of the brittle-ductile-brittle fracture modes for the HP-ST-STA specimens. In addition, the HP specimen showed only a 15% decrease in compressive strength at 973 K compared to 303 K.

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