A model for notch fatigue life

In the present work, the notch fatigue regimes of mode I fatigue crack initiation, short and long fatigue crack growth (FCG) are separated and correlated with simple appropriate parameters corresponding to each regime. A mode I fatigue crack initiated at the notch root grew with a relatively high rate and continuously slowed down until it either reached a minimum value before it increased or became non-propagating. The mode I initiation life was mathematically assumed as the number of cycles corresponding to zero crack length. Raw short mode I FCG data were best fitted and, thus, extrapolated backward to demarcate the initiation life. The initiation life obtained in the present experiments was given by the parameters of the loading cycle and the notch geometry. Thus it is possible to predict notch fatigue life, by adding the propagation and the initiation lives.