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Abstracts (International Journals and Books)

[25]   I. J. Davies, “Empirical correction factor for the best estimate of Weibull modulus obtained using linear least squares analysis”, J. Maters. Sci. Letts., 20(11) pp. 997-999 (2001).

Abstract: It is well known that the estimation of Weibull modulus, m, through linear least squares (LLS) analysis results in a systematic bias in the value of m. In the present work it has been shown that a significant decrease in this bias may be achieved by applying a simple empirical correction factor to the value of m obtained using LLS analysis. The corrected value of m was found to more closely approximate the real value of m compared to any of the fitting methods previously proposed. (Note: A later paper which includes improved analysis is available as an abstract and download)

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[24]   K. Itatani, T. Tanaka, I. J. Davies, M. Aizawa, I. Okada, H. Suemasu, and A. Nozue, “Some properties of silicon carbide composites fabricated with chopped Si-Al-C fibers”, Int. J. Maters. Prod. Tech., 16(1-3) pp. 239-247 (2001).

Abstract: Silicon carbide (SiC) ceramics possess excellent corrosion and oxidation resistances and are currently utilized as high temperature structural materials and semiconductor devices. However, due to the intrinsic brittleness of SiC ceramics, significant attention has been paid to the fabrication of long fiber-reinforced ceramic matrix composites (CMCs) in order to increase fracture toughness. Although the addition of short fibers may also enhance the fracture toughness of SiC ceramics, relatively little information on the fabrication and mechanical properties of short fiber-reinforced CMCs is available. The use of short Al-Si-C fibers in such materials is thought to be advantageous due to their heat resisting properties, e.g., ~2.7 GPa tensile strength at 1800 ^oC in an Ar atmosphere. The present work describes the fabrication and mechanical properties of high density SiC composite ceramics using various amounts of Al-Si-C short fiber addition.

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[23]   I. J. Davies and T. Ishikawa, “Estimation of the fracture toughness of Tyranno^® Si-Ti-C-O fibres from flaw size and ‘fracture mirror’ data measured in situ a 3-D woven SiC/SiC composite”, Int. J. Maters. Prod. Tech., 16(1-3) pp. 189-196 (2001).

Abstract: The fracture toughness, calculated from the size of initiating flaws, was estimated for Tyranno^® LoxM Si-Ti-C-O fibres in situ a 3-D woven SiC/SiC composite that had failed under tensile loading at room temperature. The fibres had been subjected to a surface modification treatment prior to incorporation within the composite. Two distinct flaw populations (internal and surface) were noted within the fibres with associated fracture toughness values of 0.997 (± 0.062) and 1.428 (± 0.103) MPa·m^1/2, respectively. The former value was similar to that of nominally similar Nicalon^® Si-C-O fibres whereas the latter value was attributed to the presence of an unidentified 80 nm layer surrounding the fibre.

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[22]   I. J. Davies and T. Ishikawa, “Bundle to bundle variation of mean fibre radius for Tyranno^® LoxM Si-Ti-C-O fibres”, J. Maters. Sci. Letts., 20(6) pp. 505-507 (2001).

Abstract: The aim of the present work was to determine the existence of any significant variation in mean fiber radius between nominally identical fiber bundles for a typical ceramic fiber (Tyranno^® LoxM Si-Ti-C-O). It was suggested that a small (2.5%), but statistically significant, variation of mean fiber radius existed for different fiber bundles with the noting of larger differences (20% and 15%) for the standard deviation and fractional standard deviation, respectively. Overall, the bundle to bundle variation of mean fiber radius and standard deviation appears such that additional research may be warranted into any effect this may have on the mechanical properties of composite materials.

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[21]   I. J. Davies, T. Ogasawara, and T. Ishikawa, “Stress/strain behavior of a 3-D woven composite based on the SiC/SiC system”, J. Ceram. Soc. Jpn., 109(7) pp. 643-646 (2001).

Abstract: Tensile property/strain characteristics were determined for a composite based on the SiC/SiC system (without an oxidation protection system) at room temperature and elevated temperature up to 1380 ^oC in vacuum and air. The composite consisted of surface-modified Tyranno^® LoxM Si-Ti-C-O fibres in a polymer-derived matrix. Instantaneous modulus/strain relationships were characterised by three distinct regions when tested up to 1200 ^oC in vacuum but became progressively linear at higher temperatures. Stress/strain relationships characteristic of brittle failure were generally observed at elevated temperature in air. The results were explained in terms of component and fibre/matrix interface properties together with a modified rule of mixtures equation.

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