Tensile strength and its variation for PAN-based carbon fibers. II. Calibration of the variation from testing

The tensile behavior of carbon fibers shows large scattering. This is due to the fiber itself and the testing operations. Because of the high tenacity and modulus, low strain, and easy breakability in bending, not only is the tensile test for single carbon fibers extremely difficult, but the measured results are also oppugned. To achieve a reliable and accurate characterization, several factors influencing the objective and exact testing of single carbon fibers have been measured and discussed, including the wrong pretension, nonaxial stretching, and adhesion effects. The experimental results indicate that the error of strain causing them ranges from 1.5 to 12.3%. Because of the typical linear stress-strain curves of carbon fibers, the ratio of the strain error to the modulus error is approximately equal to 1 : 1, so the calibration of the measured strain must be conducted for the accurate evaluation of the modulus and itself. The calibration is put forward. (c) 2007 Wiley Periodicals, Inc.