Andrew Briggs, Charles Lawrence and Christopher Scruby at OCAMAC and AEA Technology have been using acoustic microscopy to image cracks in ceramic fibre composites with a spatial resolution of 0.8 µm. The materials investigated so far include Nicalon SiC fibres in borosilicate glass, Tyranno silicon carbide fibres in magnesium and calcium aluminosilicates (MAS and CAS), and Textron SCS-6 silicon carbide monofilaments in a Ti-6%Al-4%V titanium alloy. Associated excitations of surface Rayleigh waves have been used to measure elastic properties and characterise the elastic contact at fibre/matrix interfaces.
In the Nicalon-borosilicate composite, acoustic images show partial fibre-matrix debonding, as well as extensive cracking around cristobalite grains formed by partial devitrification of the glass. In the heat treated SiC-Ti alloy composite, acoustic images show chemical reaction between the two components, followed by fine radial microcracking in the SiC monofilaments. In the MAS and CAS matrix composites, Rayleigh wave excitations were used to measure the in-situ shear and Young's moduli of the two components.
