Fatigue strength of PAN-based carbon fiber under cyclic loading
Horikawa Noriyo; Nakayama Hideaki; Sakaida Akiyoshi; Tanaka Tsuneshichi
Abstract:Load-controlled fatigue tests were carried out on PAN-based monofilament carbon fibers under cyclic tensile load conditions at a frequency of 10 Hz. Fatigue strength data are obtained under pre-determined maximum load Pmax with three different stress ratios of R ( = Pmin/Pmax) = 0.1, 0.5 and 0.7. The maximum load Pmax is not an appropriate parameter to evaluate the fatigue strength behavior because the cross-sectional area of monofilament carbon fiber is not constant and varies along the longitudinal direction. This fact results in a large scatter of fatigue lives when the data are plotted on Pmax-Nf diagram. In order to evaluate the fatigue strength behavior more precisely, the fatigue strength data must be plotted on S-N diagram by using the maximum tensile stress smax determined from the cross-sectional area of the fracture surface. It is found that S-N properties of monofilament carbon fibers clearly show the fatigue behavior, depending on the stress ratio R. It is also found that the fatigue strength of monofilament carbon fiber is governed by two parameters such as the maximum stress sigma max and the stress amplitude sa, and that the combined stress parameter smax(1-a)*saa is useful to describe the fatigue strength behaviors of the different stress ratios. Key Words:PAN-based carbon fiber, Monofilament carbon fiber, Fatigue test, Fatigue strength, S-N properties