MICROSTRUCTURE AND MICROMECHANICS OF THE INTERFACE IN CARBON-FIBER REINFORCED PYREX GLASS

Detailed microstructural studies have been carried out on composites consisting of Pyrex glass reinforced with carbon fibres. Analysis of the fibre-matrix interface showed that some reaction had taken place during fabrication of the composite and that a carbide or oxycarbide layer had formed between the glass and the carbon fibre. The measured interlaminar shear strength of the composite indicated that the layer was not a source of weakness and appeared to be well bonded to the matrix. Substantial fibre pull-out had occurred, however, to expose clear fibre surfaces and smooth sockets. These observations led to the conclusion that the interfacial shear process was confined substantially to the outer layers of the carbon fibre. Confirmatory evidence for the low interfacial friction stress was available from micro-indentation tests which showed fibre displacement relative to the matrix at loads of less than approximately 10 kPa. Heat treatment of the composite at 500-degrees-C in air caused preferential oxidation of the carbon fibre. Where fibres met the specimen surface, oxidation had proceeded down the fibre to produce a smoothly tapering shape. The rate of oxidation was estimated to be 3-mu-m h-1 parallel to the fibre axis, but much less than this in a direction perpendicular to the fibre, 0.5-mu-m h-1, due to the relatively slow diffusion rate of oxygen through glass.