Abstract
Three point bending tests of U-notched, V-notched and unnotched rectangular bar of ferritic spheroidal graphite cast iron were carried out. The bending strength of both notched and unnotched specimens is generally larger than the tensile strength and roughly equal to the fracture strength of the iron. The notch bending strength ratio of the U-notched specimen is 0.9 to 1.0, while that of the V-notched specimen 0.8 to 0.9. The crack initiation energy Ui, that is the bending energy required prior to the maximum load, is proportional to W01.5, where W0 stands for the width of the minimum cross section. And the ratios of Ui for U-notched and V-notched specimens to that for unnotched are 0.13 and 0.05, respectively. The crack propagation energy Up, that is the bending energy required posterior to the maximum load, is expressed as Up = 0.105 W02 for both types of notches. From the results of interrupted bending tests, the critical stress intensity factor seems to remain almost unchanged during crack propagation. The load-deflection relationship in crack propagation derived from the strength and energy also agrees well with the experimental data.
