NOMINAL AND LOCAL APPROACHES FOR THE FATIGUE STRENGTH EVALUATION OF COMPLEX COMPONENTS

摘要

The high cycle fatigue strength of blunt and sharp notches is examined both by using a nominal stress approach and a local stress approach. In the former case two diagrams are reported where the variation of fatigue strength is plotted against the ratio K_t/K_t~* or the normalised notch depth (α~2a + a_0)/a~*, a_0 being the El-Haddad length parameter, α a shape factor and, finally, a~* and K_t~* two values in correspondence of which the behaviour of sharp and blunt notches coincide. Dealing with the local approach, it is demonstrated that the stress that controls the fatigue behaviour is located at a distance from the notch tip ranging from 0.5·a_0 and 0.8·a_0, the minimum value being typical of the so-called Point Method where such a distance does not depend on the notch tip radius.