Damage model of creep-fatigue interaction

The interaction between creep and fatigue has been studied theoretically by considering a macroscopic crack, interacting with continuously distributed microdamage. This damage is a measure of an assumed deterioration of the material. A Dugdale crack model is used with most deformation and damage concentrated to narrow regions ahead of the crack tips. As studied previously, in the pure creep case, the method predicts the creep rupture curve, well known from creep rupture tests. In the pure fatigue case, the method predicts Paris' law for fatigue crack growth with an exponent approximately equal to four and a finite fatigue lifetime. In the creep-fatigue interaction case, studied here for different material parameters and external load levels, the method always predicts an interaction stronger than the linear creep-fatigue interaction.