Effect of Direction Change in Maximum Principal Strain Axis on Multiaxial Low Cycle Fatigue Life of Type 304 Stainless Steel at Elevated Temperature

摘要

Low cycle fatigue tests were carried out using cruciform specimens of Type 304 stainless steel under fully ranged multiaxial strain states at 823K. Strain paths employed in the tests were not only proportional strain histories but also severe strain histories including out-of-phase strain in order to examine the effect of stain history on multiaxial fatigue life. The crack mode was also discussed by observing the crack direction on specimen surface. For the cruciform specimen, the principal strain axes are always fixed but the maximum principal strain direction is changed into the one of three principal strain axes due to the severe strain histories. The change in direction of the maximum principal strain from one principal axis to the others had no effect on fatigue life because the additional interaction between slip systems did not occur resulting in no large additional hardening. Only the strain multiaxiality influenced the fatigue life which can be predicted as well as the multiaxial fatigue life under proportional strain histories. The strain history also did not influence the mode of crack initiation.