Creep Damage and the Remaining Life Concept

Abstract

Creep damage is described in terms of both density changes, which measure the nucleation and growth of grain boundary voids, and also changes in mechanical properties. In both cases the damage is related to the creep test variables. A loading sequence effect is demonstrated, implying that the linear life fraction rule is not applicable to creep rupture under changing stress conditions. Based on these observations, a new approach to life prediction for nonsteady temperature and stress is proposed. The principles of the new model, which is based on remaining life rather than used life, are described. It is shown how this approach requires no prior commitment to a particular damage law and that the behavior of low alloy steels, in laboratory tests and also after service operation, is consistent with the remaining life concept.