Torsional properties of carbon fibers

The torsional behavior, together with the tensile behavior, of PAN-based and mesophase pitchbased carbon fibers was studied by means of single-filament test methods, followed by scanning electron microscope examination. The torsional modulus decreased with increasing Young's modulus for both fibers. And the mesophase pitch-based carbon fibers exhibited lower torsional moduli than those of PAN based carbon fibers, in particular markedly lower moduli at higher Young's modulus. The torsional modulus depended to a large extent on the orientation structure of the graphite crystallites in the cross-section, but also upon the linking force between neighboring graphitic-layer planes. The torsional strength of both the carbon fibers increased with increasing tensile strength and that of the PAN-based carbon fibers increased as the torsional modulus increased. The spiral face of torsional fracture surfaces of the PAN based carbon fibers and the very long longitudinal faces which the torsional-fracture surfaces of the mesophase pitch-based carbon fibers have, were also considered to be associated with the orientation structures.