Evaluation of Size Effect in Low Cycle Fatigue for Q&T rotor steel

This study presents a probabilistic modeling of size effect of 30NiCrMoV12 steel in a low cycle fatigue (LCF) regime. Three types of fatigue tests have been conducted on three geometrical specimens. Results indicate that nearly all of the LCF lifetime of 30NiCrMoV12 consists of the development of multiple surface short cracks, which has shown statistical aspects of their mutual interactions and coalescence. This gives rise to an approach of LCF damage based on statistical physics. A statistical Weibull's weakest link model has been verified and a procedure for surface multiple fracture simulation is then established by including the random processes of initiation, propagation and coalescence of dispersed surface cracks. Using this procedure, the life of a component can be predicted from the criterion of critical cracks formation by coalescence of dispersed defects.