Abstract
In order to establish the fatigue life prediction method for gas turbine blades, the fatigue tests are being conducted under the intermittent strain waveform which is composed of cycling of a large pulsating strain and superposed small strain cycling. In this paper, the results of fatigue tests on Inconel 713 LC under constant amplitude strain cycling, tension hold strain cycling and intermittent strain cycling at 600°C were given.
The fatigue lives observed under the intermittent strain cycling were compared with those predicted by using the linear cumulative damage concept, and the following conclusions were obtained;
(1) The observed failure lives under the intermittent strain cycling were shorter than the predicted ones using the linear cumulative damage rule based on the failure life curve under a constant amplitude strain cycling.
(2) The observed crack initiation lives were in good agreement with those predicted by using the linear cumulative damage rule based on the crack initiation life curves under a constant amplitude and a tension hold strain cycling.
(3) The crack propagation rate under the superposed small strain cycling was accelerated by the intermittent strain. When this effect of acceleration was taken into account to the fatigue life prediction, the predicted failure lives were in very good agreement with the observed failure lives under the intermittent strain cycling.
