Extention of Creep-Fatigue Life Prediction Method based on the Overstress Concept for Multiaxial Loading

The creep-fatigue life prediction method based on the overstress concept is exteded for life evaluation under the biaxial creep-fatigue condition. The time-independent damage parameter is described by two geometically different damage parameters, one of which represents the fatigue damage in terms of a resolved overstress, and the other represents the same in terms of the overstress mormal to it. The time-dependent damage parameter is described by the maximum principal overstress. A strain rate effect is also introduced into the multiaxial creep-fatigue damage model in order to evaluate the test results with an environmental effect. The presented theory is applied to the biaxial creep-fatigue test results which were previously reported by the authors, and it is shown that the theory has a great applicability to predict the biaxial creep-fatigue life with an environmental effect within the predicability of a factor of 2.