TENSILE DEFORMATION OF CARBON-FIBERS AND THE RELATIONSHIP WITH THE MODULUS FOR SHEAR BETWEEN THE BASAL PLANES

The tensile deformation of well-oriented carbon fibers has been investigated. It is shown that the relation between stress and strain can be described by the uniform stress model. Three parameters determine the modulus and the tensile curve: the in-plane modulus of the graphite plane e1, the modulus for shear between the graphitic layer planes g, and the orientation distribution of these planes. Non-graphitized PAN-based fibers have a considerably higher shear modulus g than the pitch-based fibers. Results of structural studies indicate that this difference may be caused by covalent crosslinking. It is proposed that these crosslinks determine to a large extent the compressive strength of carbon fibers.