Abstract: The fatigue damage mechanics is used to analyze the low-cycle fatigue process of 1︰1 simulated sample of NiCrMoV steel nuclear turbine LP welded rotor. A combination analyzing method(CAM) is presented for the limitations of elastic modulus method(EM) and stress amplitude method(SAM) on the definition of fatigue damage variable, which considers material damage during cyclic softening and applies to low-cycle fatigue of cyclic softening materials and improves the accuracy of damage measurement of fatigue process. A new fatigue damage model—three stage model of fatigue damage(TSM-FD) is also proposed to analyze the low-cycle fatigue process of welded joint, which divides fatigue process of welded joint into three stages, as stress relaxation, initiation and propagation of micro hole and crack and initiation and propagation of macro crack. The results show that, in low-cycle fatigue analysis of NiCrMoV steel nuclear turbine LP welded rotor, CAM is more reasonable than EM and SAM to characterize damage variable, and TSM-FD can well describe the evolution of fatigue damage.

Key words: cyclic softening, fatigue damage model, fatigue damage variable, low-cycle fatigue, NiCrMoV, steam turbine rotor, welded joint