  Development of high strength carbon fibers (CFs) requires an understanding of
the relationship between the processing conditions, microstructure and
resulting properties. We developed a molecular model that combines kinetic
Monte Carlo (KMC) and molecular dynamics (MD) techniques to predict the
microstructure evolution during the carbonization process of carbon fiber
manufacturing. The model accurately predicts the cross-sectional microstructure
of carbon fibers, predicting features such as graphitic sheets and hairpin
structures that have been observed experimentally. We predict the transverse
modulus of the resulting fibers and find that the modulus is slightly lower
than experimental values, but is up to an order of magnitude lower than ideal
graphite. We attribute this to the perfect longitudinal texture of our
simulated structures, as well as the chain sliding mechanism that governs the
deformation of the fibers, rather than the van der Waals interaction that
governs the modulus for graphite. We also observe that high reaction rates
result in porous structures that have lower moduli.
