抄録
The main objective of this study was to make clear the value of the tensile modulus of carbon fiber with diameter variation along longitudinal direction. For this purpose, the load-elongation curves obtained in the previous report were used, in which the tensile strength was only dealt with for single fibers with the gauge lengths ranging from 2 to 100mm. It was found that the mean of tensile modulus E3 was different for different gauge lengths when the fiber diameter was determined as the minimum diameter d3 among the three diameters measured at both ends and the middle of the gauge section. The main reason is in the fact that a large variation of the fiber diameter among the gauge length was only incompletely taken into account in the definition of d3. Consequently, the equivalent diameter deq and the equivalent stress σeq and strain εeq were defined in order to give the tensile modulus E regardless of the diameter and the gauge length. Combining the two dimensional distributions of d3 and deq for respective gauge lengths obtained by the numerical diameter data of 0.1mm intervals in the previous report, and the distribution of E3 as a function of d3 together with a simple transformation equation between E and E3 including d3 and deq, the distribution of the estimated tensile modulus E for each gauge length was calculated. It was shown that the mean values E of the estimated tensile modulus E for different gauge lengths agreed very well, and the value E=195.5GPa was obtained as the most probable value of the tensile modulus for PAN carbon fiber, by averaging the value E of respective gauge lengths.
