THE INFLUENCE OF MATRIX MICROSTRUCTURE ON THE MECHANICAL-PROPERTIES OF CFRC COMPOSITES

A suite of carbon fibre reinforced carbon (CFRC) composites and carbon matrices with a range of matrix microstructures have been fabricated using a multiple liquid vacuum impregnation process and high-pressure carbonization. The carbon matrices were derived from a range of petrol eum and coal tar pitches in addition to pitch/phenolic resin mixtures. The efficiency with which the pitches densified their- respective CFR C composites was dependent initially on their carbon yield, but after repeated densification on their rheological properties. The densificat ion efficiency of the pitch/phenolic resin matrix precursors was depen dent solely on their carbon yields. The variation of phenolic resin/pi tch composition of the precursor for the matrix carbon had a profound influence on the structural and mechanical properties of the resultant carbon. The intrinsic mechanical strength (microstrength) of a matrix carbon cannot always be translated to its corresponding CFRC composit e because of fibre matrix interfacial phenomena. Studies of the system atic variation of matrix microstructure have shown that in the absence of transverse shrinkage phenomena. maximum interlaminar shear strengt h (ILSS) corresponds to a matrix of mosaic optical texture. Maximum co mpressive strength corresponds to a matrix with an axial preferred ani sotropic optical texture Consequently, it is possible to fabricate CFR C composites with specific properties by modifying their matrix micros tructures.