The dynamic longitudinal shear modulus and damping of carbon fibres

Results are presented of torsion pendulum measurements of the longitudinal shear modulus G_LT 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 G_LT or Psi _LT. Both G_LT 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 G_LT 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 G_LT for 2800 degrees C fibres.