Futoshi Nishimura

Study of Crack Propagation Behaviors on Low Cycle Fatigue in Spheroidal Graphite Cast Iron based on Observation of Surface and Fracture Section.

In order to make clear the effect of the crack coalescence for crack growth rate, low cycle fatigue tests were carried out using two kinds of spheroidal graphite cast iron (SGI). The crack propagation behaviors from the initiation crack to the fracture were investigated to observe surface and fracture section. When a main crack was connected with preexisting cracks starting from microshrinkages on neighboring surface, crack growth rate was accelerated. After connection, the rate was suppressed. So, the crack growth curve in SGI showed the state of steps. As a whole, its crack growth rate was the same as average rate in SGI. That is, the crack coalescence was not the main factor for accelerating crack growth rate. In addition, it was clear that the large variation of the crack growth curves in SGI was caused by the crack coalescence and the difference of the crack initiation length.