ON NON-HOOKEAN BEHAVIOR OF CARBON-FIBERS IN BENDING

The deformation characteristics of a range of single, large diameter pitch-based carbon fibres, and some PAN- and rayon-based fibres, were studied in elastica loop bending experiments. In pitch-based fibres, non-Hookean behaviour was found to occur at lower strains the greater the fibre anisotropy. Only elastic deformation to failure, at strains of 3%, was found for low-modulus, nearly isotropic pitch- and rayon-based fibres. The non-linear elastic behaviour in pitch-based fibres resulted 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 microcracks on the compression side of the fibres.