Evaluation of fatigue properties of high-performance fibers based on fixed-point bending fatigue test

The main aim of this article is to introduce a bending fatigue testing apparatus and a new fatigue testing method, which can be used to characterize the bending fatigue behavior of flexible materials by setting the following parameters: pre-tension, bending angle, and bending frequency. The Kevlar 49, poly(p-phenylene benzobisoxazole), Nomex, and high-performance polyethylene fibers are chosen to analyze the bending fatigue properties by the new apparatus. The cyclic stress data, number of cycle bending and bending fatigue photos are recorded during the process of the bending fatigue. The curve of the cyclic stress shows that the stress changes in periods during the cyclic bending process. The curve of the cyclic stress is theoretically analyzed. The S–N and the θ−ln N curves indicate that the pre-tension and the bending angle have significant effects on the bending fatigue life. The morphologies obtained from the digital optical apparatus can be used to explain the bending failure mechanisms of high-performance fibers. It is evident that the new bending fatigue testing apparatus is feasible and accurate in measuring and characterizing bending fatigue properties of fibers. The apparatus could effectively describe the bending fatigue lifetime and bending failure mechanisms of high-performance fibers.