Fracture behaviour in metal fibre reinforced ceramics

The aim of the work is to gain a better understanding of the microprocesses involved in the fracture of ductile phase reinforced CMCs with an interpenetrating network microstructure, especially the processes involved in deformation and fracture of the ductile phase and its subsequent influence upon overall mechanical performance of the material. A model material is produced comprising regularly orientated aluminium fibres located within an alumina matrix. Compact tension samples, each produced with fibres orientated at 30°, 60° or 90° to the fracture plane, are used to produce crack growth resistance curves and are then sliced to produce samples which are used to test the stress-extension, σ(u), behaviour of the ductile fibres. Fracture surfaces are analysed within the SEM. The σ(u) behaviour and fracture process of the fibres is modelled using both a dislocation pile-up model and FEM analysis. Comparison is made with a geometric ductile deformation model from the literature. The models are found to describe well the σ(u) experimental data and also the crack growth resistance results. It is found that ductile phase deformation and fracture is highly sensitive to the level of mechanical constraint upon the fibre. This is influenced by factors such as the porosity in the fibre, the interface strength and fibre orientation relative to the crack plane. Fibre diameter significantly affects σ(u) behaviour also.

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Fracture behaviour in metal fibre reinforced ceramics