Fracture Mechanism of Ferritic Ductile Cast Iron in Extremely Low Cycle Fatigue

Abstract

Low cycle fatigue tests were carried out under push-pull loading conditions using Ferritic Ductile Cast Iron (FDI). In order to clarify the fatigue fracture mechanism of FDI in an Extremely Low Cycle Fatigue (ELCF) regime, an observation of the longitudinal sections of the partially fatigued specimens were performed. The fatigue process in the ELCF regime can be classified into three stages : (a) Generation of micro voids, caused by the debonding of the graphite-matrix interface. (b) Growth of the micro voids, perpendicular to the loading axis. (c) Formation of an internal macro crack, due to the coalescence of micro voids inside the material. Two types of microvoid coalescence processes have been observed. The first, due to the growth of internal micro-cracks and the second, due to internal necking of the matrix. The fatigue process of the FDI in the ELCF regime was accompained by the static fracture mechanism.