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 o f Mar-M247LC directionally solidified superalloy. Tension-torsion mult iaxial low cycle fatigue tests were carried out using Mar-M247LC tubul ar specimens at 1173K in air. Several multiaxial strain and stress par ameters were applied to the experimental data to examine the suitabili ty 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 prin cipal stress and the equivalent stress based on crack opening displace ment could correlate the data within a small scatter This paper propos es a new multiaxial strain parameter which takes account of the anisot ropy 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 th e crack mode and cyclic constitutive relation of the superalloy in con nection with the anisotropy of the elastic constant.