PBnJ

2 "Crack like to blunt" notch S/N curve model Introduction In this Chapter the infinite life design philosophy of notched specimens is analyzed, then the same concepts are specialized to finite life design concepts in the context of the “Theory of the Critical Distances” to analyze the transition from “crack-like to blunt” notch. It is shown that a notched specimen behaves very similarly to a crack up to a certain number of fatigue cycles, then its fatigue behavior can be approximated with a plain specimen reduced by the effective stress concentration factor. Accordingly, some fast assessment methods have been suggested: (i) a crack like notch could be replaced by a crack for which there is a wide amount of solutions in Literature and (ii) a blunt notch could be treated through infinite life design concepts only. To verify the analytical method, the SAE Keyhole test program constant amplitude fatigue test data have been used and predictions