Abstract
In order to clarify the reason of low notch sensitivity in the strength of cast iron, tensile tests and stress analyses were performed on the circumferentially notched bars of flake and nodular cast iron. A fracture criterion was induced from the non-elastic stress distributions obtained by FEM.
The experiments showed that the rupture load of flake cast iron was varied only by ±5% at room temperature by the notches with the elastic stress concentration factor up to 2.6. Accordingly the flake cast iron showed very low notch sensitivity.
The stress analyses revealed that such low sensitivity in flake cast iron was caused by the release of stress concentration due to the non-elastic behaviour and the existence of the stress boundary layer δ of 2-3mm in depth which was proposed by the author for edge-notched plates in the previous paper. At liquid nitrogen temperature the iron showed hight notch sensitivity because of its highly elastic behaviour and the decrease in δ.
For the nodular cast iron, the rupture load of notched bars was increased by 15-25%. This increase in strength was attributed to the constraint of deformation and fracture at the notch root. According to the metallography, in the case of blunt notch, fracture initiated at the center of notch section and grew outwards in ductile manner. In the case of sharp notch, however, fracture initiated at the notch root, and the criterion with δ was applicable.
