Prediction of fatigue performance in gas turbine blades after foreign object damage

Foreign object damage is a significant cause of failure in gas turbine engines. This paper describes a series of experiments conducted on ‘blade-like’ fatigue specimens. The specimens were impacted with a cubical projectile at 250 m/s using a gas gun. They were subsequently fatigue loaded using the step method of testing to establish the fatigue strength in the damaged state. The effects of impact angle, leading edge radius, and blade wedge angle are investigated. It is shown that damage depth has a significant effect on fatigue strength. Concepts of crack arrest in the small crack regime are then used to predict the variation of fatigue strength with notch size using the Kitagawa–Takahashi diagram. The predictions are compared with the experimental results and it is shown that they constitute a lower bound. The difference between experimental and predicted results is discussed in terms of the residual stresses present close to the notch.