Estimation of Crack Initiation Life in Low Cycle Fatigue by Stress Redistribution Locus Method for Circumferential Notched Bar of Low Carbon Steel (S20C)

Abstract

The stress redistribution locus (SRL) method has been proposed to make a reasonable estimate of inelastic behavior under elevated temperatures employing both the elastic Finite Element (FE) analysis and a unique hyperbolic curve, where dimensionless equivalent strain and stress are normalized by elastic ones in the elastic FE analysis. In order to investigate applicability of the SRL method to components under the elastic-plastic state, low cycle fatigue tests were conducted employing a smooth specimen and four types of circumferentially notched bars. The number of cycles to crack initiation estimated by the SRL method was compared with the experiment. This showed that when an adequate elastic region remained inside the notch root, the crack initiation life could be well predicted by the SRL method. However when a ratio of the plastic area to the entire section of the notch root occupied over approximately 0.3%, an equivalent strain range on a surface of the notch root estimated by the SRL method became smaller than the one calculated by using the detailed inelastic FE analyses. On this occasion the crack initiation life estimated by the SRL method was overestimated.