Non‐damaging Notches in Fatigue*

The fact that very small notches (cavities, holes, scratches, etc.) have no effect on the fatigue limit of metallic materials is well known. This paper presents both a qualitative explanation for the existence of non‐damaging notches and a quantitative derivation of their critical sizes. The condition for a notch (characterized by the stress concentration factor K t and the notch root radius ρ) to be non‐damaging in a metallic material (characterized by a critical crack size l 0 ) is ( K 2 t − 1)ρ≤ 4.5 l 0 . The critical crack size can be expressed with good approximation in terms of the threshold stress intensity for fatigue crack growth and the plain fatigue limit. Therefore the above relation can be applied for an engineering evaluation of non‐damaging notches. Test results obtained for copper and a pressure vessel steel demonstrate the applicability of the proposed method.