Various aspects of localised fracture events in glass-ceramic matrices (calcium alumino-silicate (CAS) and barium magnesium alumino-silicate (BMAS)) reinforced with continuous SiC fibres (Nicalon(TM) and Tyranno(TM)) have been examined. An analytical model has been developed which enables the residual thermo-elastic stresses that are present in the composites at room temperature (as a result of the difference in coefficient of thermal expansion (CTE) between the fibres and the surrounding matrix) to be calculated. A simple consideration of the effect of introducing a free surface coupled with experimental results has shown that a portion of the fibre/matrix interface is likely to be debonded in the vicinity of the free surface. Quasi-static indentation loading of the composites has shown that lateral cracks are the predominant fracture event. The technique of confocal scanning laser microscopy has been used to provide quantitative data relating to the size of these lateral cracks as well as their sensitivity to the local fibre volume fraction. In a CAS/Nicalon composite, where the CTE of the matrix is greater than that of the fibres, lateral cracks have been found to form preferentially in regions of relatively high local fibre volume fraction. This behaviour is consistent with residual stress calculations, in that matrix in regions of high fibre volume are in a state of axial tension, which promotes lateral cracking. The converse has been found to be true in a BMAS/Tyranno system with a CTE mismatch in the opposite sense. Experiments where contact is by single particle impact have shown similar fracture patterns, suggesting that dynamic fracture follows mechanisms observed during quasi-static indentation. Utilisation of data acquired from quasi-static indentations has facilitated an upper bound prediction of the erosion wear rate. The mechanism of material removal and the estimate of wear rate have been shown to be consistent with results acquired from a limited study of erosive wear in one of the composite systems.

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Le but de ce travail est d'étudier l'effet de la teneur en cuivre et de la valence des atomes de cuivre sur la structure et les propriétés mécanique du verre. Des verres de zinc- et plomb- cuivre borate ont été étudiés. Les changements structurels avec le remplacement de PbO ou ZnO par CuO sont observés par réflectance infrarouge et Raman. L'état d'oxydation, l'environnement du site et la liaison caractéristique d'ions de cuivre ont été étudiés par spectroscopie optique et de résonance de spin électronique. Les propriétés mécaniques ont été déterminées et corrélées à la structure du verre et à sa composition, en mettant l'accent sur les propriétés élastiques, le comportement d'indentation (dureté et micro-fissures), la ténacité et la dépendance à la température de l'élasticité. Le cuivre a une tendance à stabiliser le bore en coordinence trigonale et donne une structure de type métaborate plus homogène. L'ajout d'ions de cuivre au verre métaborate améliore les performances mécaniques (modules d'élasticité et dureté), et diminue la sensibilité à la température ainsi que le taux de ramollissement des verres au plomb. Toutefois, l'ajout d'ions de cuivre dans les verres au zinc a des effets opposés sur ces propriétés. Les changements chimiques à la surface des verres de borates de cuivre et de zinc après traitement thermique sont également étudiés. L'étude par nanoindentation et par rayage montre que la couche cristallisée améliore la résistance mécanique de la surface du verre. / The aim of this work is to study the effect of copper content and copper valence on the structural and mechanical properties of glass. Zinc- and lead- copper borate glasses were studied. Their structural changes with the substitution of CuO for ZnO or PbO are followed by Raman and reflectance infrared. The oxidation state, site environment and bonding characteristic of copper ions are studied by optical and electron spin resonance spectroscopy. The mechanical properties were determined and correlated to the glass structure and composition, with a particular emphasis on the elastic properties, sharp indentation behavior (hardness and micro-cracking), toughness and temperature dependence of elasticity. Copper tends to stabilize trigonal boron and gives a more homogeneous metaborate structure. Adding copper ions to the metaborate glass clearly improves the mechanical performance (elastic moduli and hardness), in the meantime decreases the temperature sensitivity and soften rate of lead borate glasses. However, adding copper ions in zinc borate glasses has opposite effects on these properties. The chemistry changes at zinc-copper-borate glass surface after heat-treatment are also studied. Investigation of the nanoindentation and scratch behavior show that the crystallized layer improves the mechanical resistant of glass surface.