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The flexural properties of ultrahigh tensile strength polyacrylonitrile‐based (T1000GB), ultrahigh modulus pitch‐based (K13D), and high ductility pitch‐based (XN‐05) carbon fibers have been investigated using a three‐point bending test at various span lengths ranging from 200 to 1500 μm. The flexural modulus and flexural strength of these carbon fibers were measured at room temperature. The fracture surfaces under bending were examined using a high‐resolution scanning electron microscope to identify the origin of the failure. Statistical distributions of the flexural strength (maximum flexural stress at 200 μm span length) were then characterized. The Weibull modulus for the T1000GB, K13D, and XN‐05 fibers were calculated to be 11.7, 11.8, and 11.7, which is higher than those obtained from the tensile test.
Naito et al. (Fri,) studied this question.