抄録
Biaxial strain-controlled fatigue tests for 21/4Cr-1Mo steel at 550°C were performed under both proportional and nonproportional loading of combined tension and torsion, in order to examine the deformation property and the failure mode under biaxial stresses. Further, by using the results obtained, the accuracy of plastic constitutive equations and life prediction methods under biaxial stresses was investigated.
The results obtained are summarized as follows.
(1) The degree of cyclic softening under both proportional and nonproportional loading was uniformly arranged by using a parameter of ΔσASME, that is defined as the length of diagonal line in stress history.
(2) The stress-strain behavior at half fatigue life under biaxial stresses could be predicted by the combination of conventional constitutive equation and cyclic stress-strain curve under uniaxial stress.
(3) The life prediction under biaxial stresses by the equivalent strain range defined in ASME Code, was conservative.
(4) The life prediction method based on energy approach was valid for the improvement of the accuracy of life prediction under biaxial stresses.
