Bending fracture and acoustic emission studies on carbon-carbon composites: Effect of sizing treatment on carbon fibres

A comparative study using mechanical flexural tests and acoustic emission was carried out to determine the effect of carbon fibres with and without sizing treatment in carbon carbon composites during the carbonization process. The composites had been fabricated in the form of two-directional polyacrylonitrile based carbon fibres impregnated with phenolic resin. It was found that the composites made with unsized polymer fibres result in better mechanical properties. Also the data obtained from acoustic emission appeared to show that the composites made with unsized fibres were more ductile. These results may be the result of the degree of adhesion at the interface between the fibre and the matrix. The bulk density and apparent porosity were measured as functions of the number of densification cycles and the results were correlated with the mechanical test results.