ESTIMATION OF TENSILE STRENGTH DISTRIBUTION FOR CARBON FIBER WITH DIAMETER VARIATION ALONG FIBER

抄録

Tensile strength distribution of carbon fibers was investigated for different gauge lengths ranging from 2 to 100mm. In tensile tests, the fiber diameter was determined as the three-point minimum diameter d₃ at neighborhoods of 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 the tensile strength σ₀ for the true minimum diameter d₀ along the gauge length. In order to do this, two-dimensional distributions of d₃ and d₀ were derived from the data of diameter measured at every 0.1mm along a single fiber with the gauge length of 100mm. Combining these distributions of d₃ and d₀ with the distribution of the tensile strength σ₃ for the diameter d₃, the distribution of the strength σ₀ was derived analytically, and calculated by using numerical values of included parameters. The distributions of σ₀ obtained for respective gauge lengths mutually agreed very well and could be represented by a single normal distribution, and this showed the validity of the present analysis.