Fatigue Strength Evaluation of Ferritic-Pearlitic Ductile Cast Iron with Notches and Holes of Various Sizes

抄録

The fatigue strength of ductile cast iron is influenced by small defects such as graphite particles and casting defects in the material. Therefore, establishment of a reasonable predictive method of fatigue limit applicable to various shapes and sizes of defects is necessary to optimally design the ductile cast iron products. In this study, high cycle fatigue tests of sharply notched and drill-holed specimens as well as smooth specimens were performed for a ductile cast iron, JIS-FCD550, with ferrite and pearlite evenly distributed in the matrix. From the microscopic observation of the near-threshold crack growth behavior, it was revealed that the fatigue limit is determined by the threshold condition for propagation of a small crack emanating from a detrimental defect. A predictive method of the fatigue limit was presented based on a fracture mechanics approach that was composed of three different methods classified according to the defect size.