Fatigue notch sensitivity and the notch size effect

It has long been known that the fatigue notch factor KF, given by σw0/σw, where σw0 is smooth specimen fatigue strength (R = −1) and σw is the fatigue strength of a notch-containing specimen, is less than the theoretical stress concentration factor, KT. Empirical rules have been proposed by Peterson and by Kuhn and Hardrath for the estimation of KF which involve the notch radius and a material constant. El Haddad, Topper and Smith provided one means for understanding the factors determining KF. The present paper provides an alternative approach based upon a consideration of the development of fatigue crack closure. The effect of crack closure on the formation of non-propagating cracks is also discussed.