The relationship between the mechanical properties and microstructures of carbon fibers

The difference of microstructure of carbon fibers is subtle for the carbon fibers with similar mechanical properties. The mechanical properties and microstructures of six carbon fibers were investigated by a universal material testing machine, X-ray diffraction, small angle X-ray scattering and Raman spectroscopy to reveal the microstructure-dependent tensile strength of carbon fibers. Results indicate that the tensile strength increases with decreasing d002 and ID/IG and with increasing Lc for the five of the six carbon fibers. The dispersion of the tensile strength characterized by the Weibull modulus increases with increasing micropore radius. The Griffith theory over-estimates the tensile strength of the six carbon fibers. A more accurate formula was proposed based on the experimental tensile strength and microstructure of carbon fibers using Mathematics & MATLAB as the simulation tools, which takes into account of the tensile strength loss due to imperfections in the outer-surface and in the inner-surface, defects and the dispersion of fibers, and is validated by T300 data from other researchers.