A B S T R A C T Turbine blade life modelling is complicated by the presence of notches, dwells, high temperatures, thermal cycles and temperature gradients. Furthermore, directionally solidified (DS) Ni-base superalloys are highly anisotropic. This work seeks to characterize the response of the DS Ni-base superalloy CM247LC subjected to isothermal low cycle fatigue at either 750 or 950 • C. This study considers the effects of strain rate, dwells at the maximum temperature, and stress concentrations. Experiments were conducted under uniaxial loading on smooth and cylindrically notched round-bar specimens in both longitudinal and transverse orientations. The location of the creep-fatigue crack is at the maximum Hill's effective stress in the notched specimens. In addition, the notch behaviour is discussed in light of finite element analysis using an anisotropic elastic-crystal viscoplastic material model. a i = crack initiation depth: [mm] F, G, H, L, M, N = Hill parameters k t = theoretical elastic stress concentration factor N i = number of cycles to crack initiation: [cycles] N /2 = half-life cycle: [cycles] R E = ratio between tensile and compressive stiffness S = nominal stress: [MPa] σ = local stress: [MPa] ε = strain rate: [ 1 s ] or [ % s ] γ = matrix phase of a Ni-base superalloy γ = precipitate phase of a Ni-base superalloy ρ = notch radius: [mm] σ L Y S = yield strength in the L direction: [MPa] σ T Y S = yield strength in the T direction: [MPa] σ 45 Y S = yield strength in a 45 • direction: [MPa] [001] = primary crystallographic direction A B B R E V I A T I O N S ASTM = American Society for Testing and Materials CC = continuously cycled CVP = crystal viscoplasticity DS = directionally solidified HC = hold in compression Correspondence: R. W. Neu.

Fatigue life modeling of anisotropic materials such as directionally-solidified (DS) and single-crystal Ni-base superalloys is often complicated by the presence of notches coupled with dwells at elevated temperatures. This paper focuses on an approach for predicting low cycle fatigue that includes notch geometry effects while taking into consideration material orientation. An analytical model based on a generalization of the Neuber notch analysis to both multiaxial loading and anisotropic materials is used to determine the localized stress-inelastic strain response at the notch. The material anisotropy is captured through a multiaxial generalization of the Ramberg–Osgood relation using a Hill’s criterion. The elastic pseudo stress and pseudo strain response in the vicinity of the notch used as input in the Neuber analysis is determined from an anisotropic elastic finite element analysis. The effects of dwells at elevated temperature are captured using an equivalent strain rate. A nonlocal approach is needed to correlate the life of notched specimens to smooth specimens.