Estimation of tensile strength distribution for carbon fiber with diameter varying along fiber
Tanaka Tsuneshichi; Nakayama Hideaki; Sakaida Akiyoshi; Horikawa Noriyo
Abstract:Tensile strength of monofilament carbon fibers was investigated for different gauge lengths ranging from 2 to 100 mm. 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 s0 based on the true minimum diameter d0 along the gauge length. In order to do this, two dimensional distribution of d3and 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 d sub 0 with the distribution of tensile strength s3 based on the diameter d3 the distribution of strength s0 was derived analytically, and calculated using the numerical values of included parameters. The distribution of s0 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. Key Words:carbon fiber, tensile test, tensile strength, Weibull analysis, effective volume