Fatigue crack initiation and growth behavior in a notch with periodic overloads in the low‐cycle fatigue regime of FV566 ex‐service steam turbine blade material
Benjamin M. D. Cunningham, Angelos Evangelou, Chao You, A. Morris, James H. Wise, P.A.S. Reed, Andrew Hamilton
Abstract
Abstract The effect of periodic overloads on crack initiation, growth rate, and fatigue life, within a notch stress field representative of a turbine blade root fixing, has been investigated. Bend bars made from FV566 martensitic stainless steel were extracted from the root of ex‐service power plant turbine blades and representative notches introduced. These notched plain bend bars were loaded plastically in the low‐cycle fatigue regime and were tested with overloads up to 150% of the cyclic baseload every 150 baseload cycles. A periodic overload of 50% of the cyclic baseload increased the number of cycles to crack initiation and slightly retarded the crack growth rates of both short and long cracks, leading to a slight improvement in fatigue life. The results suggest that small overloads (less than 10%) are not expected to significantly impact fatigue lifetimes or service scheduling of components such as low‐pressure steam turbine blades.