The IBESS Model As a Base for Probabilistic Modeling of Fatigue Life Prediction in Cast MAR-M247 Considering Shrinkage Pores

A gas turbine (GT) operating in a renewable-integrated grid is subjected to repeated start-stop cycles and quick load ramps. Such conditions highlight a risk of potential increase of cyclic damage in its critical rotating components like the turbine blades. A multiyear government-funded project is in progress to evaluate the low cycle fatigue (LCF) behavior of a cast blade material with defects. The aim is to develop a probabilistic fatigue crack nucleation life model. Strain-controlled LCF tests were conducted on defective and defect-free flat and round specimens extracted from cast MAR-M247 GT blades [1, 2]. As the third in a continuum of publications, this paper investigated the use of the so-called IBESS model [3] as a deterministic base for a proposed probabilistic framework. Key fatigue and fracture mechanics concepts were briefly reviewed for a better understanding, followed by a detailed description of the IBESS modification of the NASGRO [4] crack growth equation. The model was applied on the data generated from the LCF tests. While the model overestimated the predictions of cycles to crack nucleation for most specimens, it showed promise for further improvements. Future work is expected to define an appropriate failure criterion and achieve better corrections for the size and geometry of both the crack and the specimen.