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 petroleum and coal tar pitches in addition to pitch/phenolic resin mixtures. The efficiency with which the pitches densified their respective CFRC composites was dependent initially on their carbon yield, but after repeated densification on their rheological properties. The densification efficiency of the pitch/phenolic resin matrix precursors was dependent solely on their carbon yields. The variation of phenolic resin/ pitch 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 composite because of fibre matrix interfacial phenomena. Studies of the systematic variation of matrix microstructure have shown that in the absence of transverse shrinkage phenomena, maximum interlaminar shear strength (ILSS) corresponds to a matrix of mosaic optical texture. Maximum compressive strength corresponds to a matrix with an axial preferred anisotropic optical texture. Consequently, it is possible to fabricate CFRC composites with specific properties by modifying their matrix microstructures.