ABSTRACT
In the previous chapter, we have built the analytical framework for considering time-dependent creep deformation in the crack tip region and have used the analyses to define crack tip parameters for predicting crack growth under the conditions of sustained loading. Cyclic or fatigue loading is quite prominent in several components that are operated at elevated temperature, making crack growth behavior under creep–fatigue conditions quite important. Figure 9.1 shows a schematic diagram of a section of a steam header in which the high stress locations are marked and the load/stress versus time history experienced at these locations during one complete operating cycle of the header is also shown [1]. Such duty cycles involving combination of time-varying stress, periods of sustained stress, and high temperatures are typical of several elevated temperature components. Creep deformation can occur during both the sustained load period and during the loading/unloading portion of the cycle.
