Evaluation of Small Bulge Fatigue Crack Propagation Behavior of Type 316 Steel by Finite Element Analysis

The crack propagation analysis was carried out using the finite element method to investigate the causes of the characteristic crack shape formation and crack propagation behaviors observed in the SBF (small bulge fatigue) test with Type 316 steel. Specifically, several crack models simulating the SBF crack propagation process were created to investigate the effects of crack shape and branch angle on the stress intensity factor and the energy release rate. The analytical results showed that the energy release rate, which had been calculated by the stress intensity factor obtained by the analysis, increased with increasing branch angle, and this increase in energy release rate seemed to be a driving force behind the branching of SBF crack. It could be also explained by the maximum tangential stress theory that the crack propagated with opening angle of 90° and the SBF specimen was macroscopically divided into four pieces after the test. In addition, the experimentally measured crack propagation rate, da/dN, was relatively well correlated with the analytically obtained maximum stress intensity factor, Kmax.