Oxidation-involved life prediction and damage assessment under generalized creep-fatigue loading conditions based on engineering damage mechanics

The object of this paper is to develop numerical procedures for creep-fatigue-oxidation life prediction and damage assessments based on engineering damage approach, in response to high-reliability and long-life design requirement that supports low-carbon and new-energy technologies. In order to achieve the prediction results in terms of cycle-dependent stress–strain responses, crack initiation life prediction and multi-damage evolutions, the generalized creep-fatigue loading conditions including tension-hold-only, compression-hold-only and tension-compression-hold-both, which are abbreviated as CP, PC, and CC types, are conducted for IN 718 at 650 °C. Results show that creep-fatigue deformation behaviors are well depicted through the evolutions of hysteresis loops, cyclic softening curves and stress responses. With incorporating into oxidation damage especially under long-life conditions, both error band and probability density function for life prediction are quantitatively improved. In addition, the cycle-dependent roles in multi-damage evolutions are clearly observed in a set of radar graphs, where fatigue, creep and oxidation damage are manifested as different evolutionary features. Finally, the technical route in the transition from deterministic to probabilistic multi-damage assessments is discussed based on the established creep-fatigue-oxidation diagram.