TEMPERATURE AND PRESSURE-DEPENDENCE OF THE CONDUCTIVITY ANISOTROPY OF UNIDIRECTIONAL SHORT CARBON-FIBER FILLED POLYMERS

An experimental study of the effects of temperature and pressure on the conductivity anisotropy of aligned short carbon fiber filled epoxies is presented. The data give evidence of significant relative changes of the anisotropy whose sign and amplitude depend on the volume concentration near the conductivity threshold. A phenomenological approach involving variations with temperature and pressure of the fiber volume fraction and the fiber aspect ratio is developed. It predicts that the anisotropy change results from two competing contributions in a similar way whether the temperature or the pressure is varied. Although quantitative predictions cannot be made, we show that introducing the available mechanical and thermal materials constants into the theoretical equations accounts, at least qualitatively, for the experimental behaviors.