Ultra low-cycle fatigue fracture initiation prediction of X80 pipeline steel using a modified cyclic void growth model

Abstract

The ULCF tests of X80 pipeline steel were carried out in the range of high stress triaxiality. The inapplicability of CVGM was observed by evaluating the ultra-low cycle fatigue (ULCF) fracture initiation of X80 pipeline steel due to the excessive discrepancy in strain hardening behaviors between monotonic and cyclic loadings. The effect of the discrepancy on the application of CVGM was discussed. Then, a modified CVGM was proposed to overcome the limitation of the original CVGM. Besides, the experimental results reveal that the critical cyclic void growth index is related to stress triaxiality, and a stress triaxiality correction term was also introduced. The result showed that the developed model can predict the ULCF fracture initiation of X80 pipeline steel within a 25% margin.