An overview of the damage approach of durability modelling at elevated temperature

Lifetime prediction techniques for components working at elevated temperatu re are revisited. Two damage approaches in which time effects at high tempe rature are introduced in different ways are discussed in greater detail. Fi rst, a creep-fatigue damage model considers the interaction of the two proc esses during the whole life before macrocrack initiation; and second, a cre ep-fatigue-oxidation model separates the fatigue life into two periods: dur ing initiation the environment-assisted processes interact with fatigue, al though bulk creep damage only interacts during the micropropagation period. The second model is illustrated by its application to a coated single-crys tal superalloy used in aerojet turbine blades. Its capabilities are illustr ated in a number of isothermal and thermomechanical fatigue tests. Anisotro py effects are also briefly discussed and a special test, introducing cycli c thermal gradients through the wall thickness of a tubular component, demo nstrates the predictive capabilities for actual engine conditions.