ON NON-HOOKEAN BEHAVIOR OF CARBON-FIBERS IN BENDING

The deformation characteristics of a range of single, large diameter p itch-based carbon fibres, and some PAN- and rayon-based fibres, were s tudied in elastica loop bending experiments. In pitch-based fibres, no n-Hookean behaviour was found to occur at lower strains the greater th e fibre anisotropy. Only elastic deformation to failure, at strains of 3%, was found for low-modulus, nearly isotropic pitch- and rayon-base d fibres. The non-linear elastic behaviour in pitch-based fibres resul ted in pronounced hysteresis and discontinuities in the stress-strain plots on both unloading and reloading the loops. These effects are due to the initiation, propagation and possible healing of transverse mic rocracks on the compression side of the fibres.