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Abstracts (International Journals and Books)

[40]   I. J. Davies, “Best estimate of Weibull modulus obtained using linear least squares analysis: An improved empirical correction factor”, J. Maters. Sci., 39 pp. 1441-1444 (2004).

Abstract: Empirical correction factors have been calculated that significantly reduce the bias in the value of Weibull modulus obtained using linear least squares analysis. It is hoped that the relatively simple nature of the correction factors will promote widespread use in the materials science and engineering communities.

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[39]   I. J. Davies, G. Pezzotti, A. Bellosi, D. Sciti, and S. Guicciardi, “Mechanical behaviour of nickel aluminide reinforced alumina (Al₂O₃ - NiAl) composites”, Adv. Composites Letts., 11(6) pp. 265-273 (2002).

Abstract: The microstructure and mechanical properties of hot-pressed alumina (Al₂O₃) matrix composites containing 25, 25, or 50 vol% of nickel aluminide (NiAl) was investigated. The mean Al₂O₃ grain size was found to decrease from ~2.0 mm (monolithic Al₂O₃) to ~1.0 mm for the composite containing 50 vol% NiAl. Composite flexural strength and elastic modulus values were lower than both the monolithic Al₂O₃ and NiAl and attributed to the weakly bonded NiAl particles acting as flaw origins and microcracks or microvoids, respectively. The fracture toughness increased with NiAl content to a maximum of 4.90 MPa·m^1/2, thus confirming the toughening effect of NiAl addition on Al₂O₃ ceramics. The slope of the rising R-curve for the composite was approximately 8 times that of monolithic Al₂O₃. The electrical conductivity increased almost linearly with NiAl content and indicated the absence of interconnectivity even for 50 vol% of the NiAl phase.

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[38]   K. Itatani and I. J. Davies, “Mechanical properties of silicon carbide composites fabricated with short inorganic fibers”, Recent Res. Devel. Maters. Sci., 3 pp. 427-439 (2002).

Abstract: Silicon carbide (SiC) composites reinforced with 10~50 mass% (19.3~54.4 vol%) of short Tyranno^® Si-Zr-C-O and Si-Al-C fibres (mean length ~0.4 and ~0.5 mm, respectively) and 5 mol% of Al₄C₃ sintering aid were fabricated using the hot-pressing technique (1800 ^oC/31 MPa/30 min). Although the relative density was only 87.4% for the composite containing 10 mass% of Si-Zr-C-O fibre, additional increases in the amount of Si-Zr-C-O fibre resulted in a maximum relative density of 92.8% for 40 mass% of fibre addition. The fracture toughness of SiC specimens containing 20~40 mass% of Si-Zr-C-O fibre addition was in the range 3.2~3.4 MPa·m^1/2 and approximately 1.5 times that of the monolithic SiC (2.4 MPa·m^1/2). In contrast to this, SiC composites reinforced with 30 mass% of Si-Al-C fibre showed a maximum relative density of 96.8% amongst the specimens examined. The maximum values of fracture toughness and Vickers hardness for this composite were 3.9 MPa·m^1/2 (30 mass% fibres) and 28.3 GPa (40 mass% of fibres), respectively. Furthermore, the fracture toughness of the composites was further enhanced to 5.8 MPa·m^1/2 through the use of 30 mass% of carbon-coated Si-Al-C fibres.

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[37]   I. J. Davies and T. Ishikawa, “Comparison between predicted and experimental stress/strain behaviour for a 3-D woven SiC/SiC composite tested between room temperature and 1300 ^oC”, J. Maters. Sci. Letts., 21(6) pp. 461-463 (2002).

Abstract: Experimental and theoretical tensile stress/strain curves were compared for a 3-D woven SiC/SiC composite up to 1300 ^oC in vacuum and 1200 ^oC in air. A reasonable correlation existed between experimental and theoretical curves for unsealed (room temperature and 1200 ^oC) and glass-sealed (1000 and 1200 ^oC) specimens. The deviation between composite strength values was 5.2% and similar to that noted by previous researchers while the deviation between maximum strain values was slightly higher at 8.8%. The difference between experimental and theoretical curves for the unsealed specimen tested at 1300 ^oC in vacuum was attributed to thermal decomposition and a subsequent decrease (~20%) in tensile modulus of the fiber at this temperature.

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[36]   I. J. Davies and T. Ishikawa, “Mirror constant for Tyranno^® silicon-titanium-carbon-oxygen fibers measured in situ in a three-dimensional woven silicon carbide/silicon carbide composite”, J. Amer. Ceram. Soc., 85(3) pp. 691-693 (2002).

Abstract: The strength, S, of ceramic and glass fibers may often be estimated from fractographic investigation using the fracture mirror radius, r_m, and the relationship S=A_m/(r_m)^1/2, where A_m is known as the “mirror constant”. The present work estimated the value of A_m for Tyranno^® Si-Ti-C-O fibers in situ a 3-D woven SiC/SiC-based composite to be 2.50 (±0.09) MPa·m^1/2. This value is within the range of 2~2.51 MPa·m^1/2 previously obtained for nominally similar Nicalon^® Si-C-O fibers.

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