Fatigue Damage Process of Spheroidal Graphite Cast Iron Under Rotating Bending Cyclic Loading

Residual strength tests were carried out on spheroidal graphite cast iron by means of a rotating bending fatigue test machine. In order to study the fatigue damage process, the scatter of the test data was estimated by means of Weibull distributions, and also, fatigue crack propagation behaviors and crack length distributions on the surfaces of the smooth specimens were investigated. For each testing of the two stress levels 294.3 MPa and 245.3 MPa, thirteen specimens were used in order to obtain the exact fatigue lives. The residual strength tests were conducted on the basis of these fatigue lives at the two stress levels. The dispersion of residual strength and residual strength degradation for the stress level 294.3 MPa occurred from the stage of cycle ratio 0.5. The cumulative probability of crack length distribution for each cycle ratio at the stress level 294.3 MPa showed that the distributions of longer crack length increase as cycle ratio increases. The greatest cause of the scattering of residual strength was considered to be the occurrence of various long cracks.