Fatigue Fracture Mechanism of Thin Wires of Commercially Pure Iron under Cyclic Bending

Abstract

In the present study, fatigue fracture behavior of commercially pure iron thin wires with the diameter of 700 μm was investigated under cyclic bending by using a bending fatigue testing system developed for thin wires. At bending moment ratio M_min/M_max = －1, －0.8, －0.6 and －0.2, microscopic observation of fracture surface shows striations. Therefore fatigue cracks initiated at both the upper and lower surfaces and propagated toward the neutral axis of the specimen. On the other hand for tension-tension fatigue with the stress ratio R = 0.1, ratcheting failure and necking were occurred and the initiation and propagation of fatigue crack were not observed.