Tensile strength of monofilament carbon fibers was investigated for different gauge lengths ranging from 2 to 100mm. In the tensile tests, the fiber diameter was determined as the minimum diameter
d3 at both ends and the center of gauge section by using an optical microscope. Weibull analysis of the data and the effective volume model for tensile strength of carbon fiber showed that the shape parameter
a was not constant for different gauge lengths and the effective volume model could not be applied effectively to the results. It was found that these were caused by the fact that the diameter was never constant along a carbon fiber. Consequently, in this study, it was aimed to derive the distribution of tensile strength σ
0 based on the true minimum diameter
d0 along the gauge length. In order to do this, two dimensional distribution of
d3 and
d0 was derived from the data of diameter measured at every 0.1mm along a single fiber of 100mm assuming the normal distribution. Combining this distribution of
d3 and
d0 with the distribution of tensile strength σ
3 based on the diameter
d3, the distribution of strength σ
0 was derived analytically, and calculated using the numerical values of included parameters. The distribution of σ
0 obtained for the respective gauge lengths mutually agreed very well and could be represented by a single normal distribution, showing the validity of the present analysis.
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