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Abstracts (International Journals and Books)

[30]   O. Sbaizero, S. Maschio, G. Pezzotti, and I. J. Davies, “Microprobe fluorescence spectroscopy evaluation of stress fields developed along a propagating crack in an Al₂O₃/CaO.6Al₂O₃ ceramic composite”, J. Maters. Res., 16(10) pp. 2798-2804 (2001).

Abstract: The fracture behavior upon stable crack propagation in bending was investigated for a ceramic matrix composite comprising 15 vol% of calcium hexaluminate (CaAl₁₂O₁₉ or “CA6”) in an Al₂O₃ matrix and compared to the crack bridging stresses as measured by microprobe fluorescence spectroscopy. In addition, piezo-spectroscopy coefficients of -4.57 and –3.79 cm^-1GPa^-1 were determined for the peaks located at 14488 and 14528 cm^-1, respectively, for monolithic CA6. It was concluded that the macroscopic R-curve behaviour of the composite could be predicted from microscopic bridging stress data and indicated microprobe fluorescence spectroscopy to be a significant experimental tool for the investigation of fracture micromechanisms in ceramic materials.

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[29]   I. J. Davies and H. Hamada, “Flexural properties of a hybrid polymer matrix composite containing carbon and silicon carbide fibres”, Adv. Composite Maters., 10(1) pp. 77-96 (2001).

Abstract: The flexural properties of hybrid unidirectional fibre reinforced polymer (FRP) composites containing a mixture of carbon (C) and silicon carbide (SiC) fibres were evaluated at span to depth (S/d) ratios of 16, 32, and 64. The flexural strength generally increased with increasing S/d ratio with a maximum value of 2316 MPa being achieved for the specimen with nominally equal volume fractions of C and SiC fibre. However, even replacing 12.5 vol% of the C fibres by SiC fibres increased the flexural strength by 22%. The mechanical property most strongly influenced by the incorporation of SiC fibres was the work of fracture with a maximum value of 206.5 kJ·m^-2 (compared to 78.8 kJ·m^-2 for the specimen containing only C fibres). First estimate values for the SiC fibre compressive strength, elastic modulus, and strain to failure were 3.46 GPa, 157 GPa, and 0.018, respectively.

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[28]   I. J. Davies, “Effect of radius variation on the mean strength of brittle fibres”, J. Maters. Sci. Letts., 20(12) pp. 1103-1105 (2001).

Abstract: The present work is concerned with the derivation of mean strength for brittle fibers with varying radii and its applicability to simulated populations of brittle fibers. Whilst the case of brittle fibers has been examined, the theory may be easily adapted to any brittle material whose dimensions vary by a known amount. The main conclusion of this work is that the mean strength of brittle fibers increases with the variability of fiber radii; this effect being most prominent when theWeibull modulus is smallest. However, the degree of increase is such that it can, for all practical purposes, most likely be ignored.

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[27]   K. Itatani, K. Hattori, D. Harima, M. Aizawa, I. Okada, I. J. Davies, H. Suemasu, and A. Nozue, “Mechanical and thermal properties of silicon-carbide composites fabricated with short Tyranno^® Si-Zr-C-O fibre”, J. Maters. Sci., 36(15) pp. 3679-3686 (2001).

Abstract: Silicon carbide (SiC) ceramics reinforced with 10~50 mass% of short Tyranno^® Si-Zr-C-O fibre (average length ~0.5 mm) and 0~10 mol% of Al₄C₃ as a sintering aid were fabricated using the hot-pressing technique. Firstly, the effect of Si-Zr-C-O fibre addition on relative density (bulk density/true density) for composites hot-pressed at 1800 ^oC for 30 min was examined by fixing the amount of Al₄C₃ to be 5 mol%. Although the relative density was reduced to 87.4% for 10 mass% of Si-Zr-C-O addition, further increases in the amount of Si-Zr-C-O fibre increased density to a maximum of 92.8% at 40 mass% of fibre addition. Secondly, the effect of varying the amount of Al₄C₃ addition on the relative density was examined by fixing the amount of Si-Zr-C-O fibre to be 40 mass%. The optimum amount of Al₄C₃ addition for the fabrication of dense composite specimens was found to be 5 mol%. The fracture toughness of the hot-pressed composites with 20~40 mass% of Si-Zr-C-O fibre addition was 3.2~3.4 MPa·m^1/2 and approximately 1.5 times higher than that (2.39 MPa·m^1/2) of the hot-pressed monolithic SiC specimen. SEM observation showed evidence of Si-Zr-C-O fibre debonding and pull-out at the fracture surfaces. The hot-pressed composite with 5 mol% of Al₄C₃ and 40 mass% of Si-Zr-C-O fibre additions showed excellent heat-resistance at 1300 ^oC in air due to the formation of a SiO₂ layer at and near exposed surfaces.

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[26]   T. Ogasawara, T. Ishikawa, H. Ito, N. Watanabe, and I. J. Davies, “Multiple cracking and tensile behavior for an orthogonal 3-D woven Si-Ti-C-O fiber/Si-Ti-C-O matrix composite”, J. Amer. Ceram. Soc., 84(7) pp. 1565-1574 (2001).

Abstract: This paper presents experimental results for the multiple microcracking and tensile behavior of an orthogonal 3-D woven Si-Ti-C-O fiber (Tyranno™ Lox-M)/Si-Ti-C-O matrix composite with a nanoscale carbon fiber/matrix interphase and processed using a polymer impregnation and pyrolysis route. Based on microscopic observations and unidirectional tensile tests, it is revealed that the inelastic tensile stress/strain behavior is governed by matrix cracking in transverse (90°) fiber bundles between 65 and 180 MPa, matrix cracking in longitudinal (0°) fiber bundles between 180 and 300 MPa, and fiber fragmentation above 300 MPa. A methodology for estimation of unidirectional tensile behavior in orthogonal 3-D composites has been established by the use and modification of existing theory. A good correlation was obtained between the predicted and measured composite strain using this procedure.

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