Stress field parameters to predict the fatigue strength of notched components

The stress field parameters, namely the notch stress intensity factors (N-SIFs) according to a more recent definition, can be used to predict the fatigue behaviour of mechanical components weakened by V-shaped re-entrant corners, where the singularity in the stress distribution makes any failure criterion based on the elastic peak stress no longer applicable. When the notch root radius is small but different from zero, the N-SIF can still be used, since a comprehensive analytical approach is available for open sharp and blunt notches. The fatigue strength reduction factor can be given as a function both of the elastic peak stress (only if it has a finite value) and of the N-SIF (for every notch tip radius value), by assuming that the fatigue strength of notched elements depends on a mean stress value in the critical zone. The welded joints are an example of practical N-SIF use in fatigue strength prediction. In this case not only the fatigue crack initiation life but also the fatigue crack propagation phase are strictly correlated to the N-SIF value for the reason that the residual life is mainly dependent on crack propagation in the zone just governed by N-SIFs.