scope:

Low-cycle strain controlled fatigue tests were performed on lCr-lMo-l/4V rotor steel at 1000F (538C) under uniaxial and a biaxial state of stress corresponding to plane strain. The plane strain test specimen was a compact tension specimen containing a blunt notch. An elastic-plastic finite element analysis of the specimen was used to evaluate the strain at the notch tip as a function of the notch opening displacement which was controlled in the tests. Crack initiation results for the two stress conditions were examined in terms of the triaxiality factor, effective strain, octahedral shear strain and modifications of the constants in the Coffin-Manson plastic strain-life relation. The triaxiality factor approach showed excellent correlation for higher plastic strains and tended to be somewhat conservative in life prediction beyond lo4 cycles. The results were extended to other biaxial stress conditions.