Tension-Torsion Multiaxial Low Cycle Fatigue of Mar-M247LC Directionally Solidified Superalloy at Elevated Temperature

This paper studies the high temperature multiaxial low cycle fatigue of Mar-M247LC directionally solidified superalloy. Tension-torsion multiaxial low cycle fatigue tests were carried out using Mar-M247LC tubular specimens at 1173K in air. Several multiaxial strain and stress parameters were applied to the experimental data to examine the suitability of the parameters. All the multiaxial strain parameters proposed so far could not successfully correlate the multiaxial low cycle fatigue data of the directionally solidified superalloy, but the maximum principal stress and the equivalent stress based on crack opening displacement could correlate the data within a small scatter. This paper proposes a new multiaxial strain parameter which takes account of the anisotropy of elastic constant of directionally solidified superalloys. The proposed strain parameter correlates the multiaxial low cycle fatigue data within a factor of two scatter band. This paper also describes the crack mode and cyclic constitutive relation of the superalloy in connection with the anisotropy of the elastic constant.