DAMAGE CHARACTERIZATION OF 2-DIMENSIONAL WOVEN AND 3-DIMENSIONAL BRAIDED SIC-SIC COMPOSITES

A comprehensive investigation of the room temperature behaviour of two -dimensional woven and three-dimensional braided SiC-SiC composites fa bricated by the chemical vapour infiltration route has been conducted. A morphological study of the residual porosity in the composites reve aled the existence of primarily two populations of pores: small intray arn pores and larger interyarn pores. The sizes and the shapes of the two types of pores depended largely on the fibre architecture; the two step braided composite in which the majority of the fibre yarns were orientated along the axial direction exhibited the smallest pore size. The pore size and shapes in turn influenced the onset of damage in th e composites under tensile loading. Damage was found to be initially m atrix dominated, thus being essentially independent of the fibre archi tecture. At higher stress levels, however, fibre dominated damage prev ailed. Unlike the tensile behaviour, where damage led to non-linearity in the stress-strain curve, the compressive behaviour of the composit es was linear elastic almost up to failure. The off-axis tensile prope rties as well as compression after tension behaviour of the two-dimens ional woven composites were also investigated. The information obtaine d from these tests provides the basis for the modelling of damage in t hese materials.