ACOUSTIC MICROSCOPY OF CERAMIC-FIBER COMPOSITES .2. GLASS CERAMIC-MATRIX COMPOSITES

Two silicon-carbide-fibre composites, one with a magnesium-aluminosili cate matrix and the other with a calcium-aluminosilicate matrix, were studied using acoustic microscopy. Contrast was found between the fibr es and the matrix, and there was, in addition, a distinctive contrast associated with the boundary between them. In some cases the contrast at the boundary was characteristic of a well-bonded interface, and in others it was characteristic of a crack; strong contrast was also foun d from cracks in both the matrix and the fibres. It was possible to ob tain a good quantitative fit between observation and theoretical calcu lations of boundary contrast. Radial cracks and radial variations of t he microstructure in the fibres were studied. From measurements of fri nges in the areas of contrast and estimates of Poisson's ratio, values of the shear modulus and Young's modulus could be deduced; independen t values from nano-indentation measurements were in good agreement. So me of the calcium-aluminosilicate composites were studied after strain ing below and beyond the elastic limit; and the appearance of cracks w as related to a theoretical model, yielding a value for the interfacia l strength within the range of reported values.