Fatigue Life Modeling of Anisotropic Materials Using a Multiaxial Notch Analysis

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.