The change of elastic modulus and stress associated with fatigue cyclic number was investigated during low cycle fatigue.The research shows that

the low cycle fatigue damage can be determined by the change of elastic modulus and stress.For the materials

which have no cyclic steady stage but exhibit cyclic softening

this method isn't suitable to determine the low cycle fatigue damage with the change of stress.The fatigue crack initiation life was acquired by the change of elastic modulus under different strain levels

so the relationship between strain and fatigue crack initiation life was determined by three parameters power equation.