The dynamic longitudinal shear modulus and damping of carbon fibres

Results are presented of torsion pendulum measurements of the longitudinal shear modulus GLT and damping Psi LT of single carbon fibres in the frequency range 0.01-0.1 Hz. Cyclic surface shear strains up to 10-3 had no noticeable effect on either GLT or Psi LT. Both GLT and Psi LT increase in the presence of an axial tensile stress. A detailed investigation was made of the effects of heat treatment temperature on a range of fibres from polyacrylonitrile to those graphitized at 2800 degrees C. There was a rapid increase in GLT and a corresponding decrease in Psi LT up to 1000 degrees C, this being associated with cross-linking. Above 1000 degrees C, neither property changed appreciably except for a slight, but significant, reduction in GLT for 2800 degrees C fibres.