Evaluation and prediction of crack length in a Ni-based superalloy for sustained loading
2014 (English)Manuscript (preprint) (Other academic)
Crack length evaluations for sustained loading have been conducted on Inconel 718 surface crack specimens for 550 and 650 ◦C. Hold times, e.g. slow ramp up of engine thrust, sustained load as continuous power output for stationary gas turbines or as cruise for aero engines, have been seen to result in material damage at the crack tip, causing the crack to grow by intergranular fracture and resulting in a strong increase of the crack growth rate. Here, sustained load tests as well as specially designed hold time tests are used to measure crack length and the size of the damaged zone (material damage) in front of the crack tip by comparing potential drop (PD) predictions with visible post-mortem beach marks on the fracture surface. Fracture surfaces were also investigated with scanning electron microscope (SEM), showing what the damaged zone most likely consists of. In addition, by applying a crack propagation model based on the damaged zone concept, crack length and damaged zone evaluations were conducted. The results show that the damaged zone must be taken into consideration, when evaluating post-mortem fracture surfaces if the test has included hold time loads, both when setting up post-mortem calibration curves and when evaluating crack propagation models.
Place, publisher, year, edition, pages
Fatigue crack propagation, Inconel 718, Sustained load, Hold time effects, Crack length evaluation
Engineering and Technology
IdentifiersURN: urn:nbn:se:liu:diva-104813OAI: oai:DiVA.org:liu-104813DiVA: diva2:699339