Life Prediction for Creep‐fatigue Based on the Growth of Short Cracks

For two types of steels (comparable to the 304‐type and 347‐type of steels) the nucleation and growth of short surface cracks was examined as a function of hold‐time, strain rate, and temperature. In addition, for the same range of parameters, damage parameter vs cycles to failure curves were calculated from measured lifetimes. The measured rates, dα/dN, were compared with a model for the growth of creep‐fatigue cracks. At large strains, life was found to be dominated by the growth of short cracks. The life data were compared with the life calculated from the crack growth data. The results showed that except for cases in which crack growth is controlled by the coalescence of cavities, the specimen life can be predicted correctly by integrating the growth rate of microcracks.