Relationship between notch strengthening threshold and mechanical property for ductile cast iron

In this study, dynamic tensile tests were conducted at the various strain rates and temperatures for traditional ductile cast iron. Then, the notch strength ${\sigma }_B^{noth}$ and the static tensile strength at room temperature ${\sigma }_{B,RT}^{smooth}$ were discussed in terms of the strain rate- temperature parameter R, which is known to be useful for evaluating the combined influence of strain rate and temperature. This study focuses on the notch strengthening threshold R ≧ R _th where ${\sigma }_B^{noth}$ is larger than ${\sigma }_{B,RT}^{smooth}$ and therefore notched components can be used safely. In other words, if R ≧ R _th, ${\sigma }_{B,RT}^{smooth}$ can be used to evaluate notched components in mechanical design to prevent the instantaneous fracture. In this study, it was found that the R _th value can be predicted from the static tensile property and Brinell hardness. Since the traditional ductile cast iron considered in this paper has a broad range of mechanical properties, the present approach and discussion can be applied to evaluate other materials under various temperature and strain rate. (paper)