Prediction of fatigue initiation lives in notched Ti 6246 specimens

This paper focuses on the application of numerical models for predicting LCF initiation lives in notched Ti 6246 specimens tested in air at ambient and elevated temperatures. Model predictions are based on the results of un-notched strain control specimens and rely on the assumption that, for an equivalent stress–strain state, both notched and plane specimens exhibit the same initiation lives. A number of fatigue initiation criteria have been developed based on the strain control testing of plane specimens. These include: (1) a Walker strain-based parameter; (2) Smith–Watson–Topper (SWT) parameter; and (3) the strain energy-based method of Golos and Ellyin. Both the Neuber method and non-linear finite element analysis are used to provide numerical values for the stress–strain state at the root of the notched specimens, and hence prediction of fatigue crack initiation lives through correlation with the fatigue criteria. The predictive capability of each criterion is examined and assessed and some of the issues relating to the prediction of initiation of fatigue cracks in notches are highlighted, including the impact of mean stresses, temperature and the accuracy of the Neuber and finite element methods used to model the mechanical response within the notches.