Abstract
This paper describes the crack growth direction and fatigue life behavior in creep-fatigue conditions under biaxial stress states. In order to examine creep-fatigue interactions, Mises' type equivalent stress controlled tests with the hold time of 0, 10, 30 and 60min. at the peak strain were carried out using the hollow specimens of austenitic stainless steel SUS304 at the strain rate 0.1%/s at 923K in air. The conclusions obtained were as following.
(1) The main crack growth direction in the no-hold time test changed from the direction perpendicular to the maximum principal strain to the maximum shear direction at the principal strain ratio -0.7<φ<-0.8. However, in the tests with hold time the transition point of crack growth direction shifted to the reversed torsion side.
(2) The effect of strain hold time on push-pull mode was more pronounced than that of reversed torsion.
(3) By applying the linear damage rule obtained from the stress relaxation curve of Mises' type equivalent stress basis to biaxial creep-fatigue data, the fatigue lives of the reversed torsion tests were predicted and found significantly conservative because creep damage is over estimated. But those by COD based equivalent stress basis provided satisfactory prediction.
