Fatigue crack acceleration and retardation induced by high temperature load hold in Inconel 718

Abstract

The effect of high temperature tension hold on fatigue crack growth in Inconel 718 is investigated. A single tension hold at maximum load was applied during cyclic loading at 650 °C, and the effect of load level and hold time are examined. In all experiments, a rapid acceleration of fatigue crack growth is observed immediately after tension hold. A retardation is observed after the initial acceleration at lower stress intensity factors, while only an acceleration occurs at higher intensity factors. These results are discussed by considering two competed mechanisms: grain boundary damage related to oxygen in front of the crack tip, and stress relaxation due to creep deformation.