Ceramic composites deform in tensile states of stress by matrix microcracking. The deformation of SiC-Al2O3 and SiC-SiC composites has been modelled in two ways. Firstly a computational damage mechanics approach has been developed. In the analysis the effect of individual cracks is represented by a damaged continuum. This approach is valid over size scales which encompass multiple matrix micro-cracking, and does not attempt to model the response of a component to a single dominant crack. The damage analysis is compared with an experimental approach based on a polymer analogue of the ceramic composite. The polymer composite system has no modulus mismatch between fibre and matrix and exhibits similar deformation modes to the ceramic systems. In the computational model, micro-cracking and flow in tension and compression were represented by intersecting Mohr-Coulomb, yield, or micro-cracking surfaces. The computational model allows orthogonal arrays of cracks to be formed normal to the directions of maximum principal strain associated with the crack formation surface. This model was refined to incorporate the anisotropic effects of fibres with the introduction of reinforcing elements. Subsequent deformation was described by a combination of an incrementally damaged elastic stress-strain relationship and a classical elastic plastic relationship. The results of numerical modelling were compared with experiments on ceramic composites and the model polymer systems. The unrefined micro-damage constitutive model was also used to analyse a component of an exhaust diffuser unit of a modern air breathing engine and to discuss the micro-mechanics of single dominant crack growth in a ceramic composite.
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The Experimental and Computational Modelling of the Deformation of Ceramic Composites
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