Fatigue notch factor and short crack propagation

This paper addresses the problem of high cycle fatigue at notches and the role of short crack propagation in the fatigue notch factor kf. Ahead of a V-notched feature, the stress field is characterized by two parameters, i.e. the stress concentration factor kt and the normalized notch stress intensity factor kn. Whether fatigue strength at a given life is controlled by crack initiation (kf = kt) or by short crack propagation (kf < kt) depends on kt, kn and the material resistances to crack initiation and to short crack propagation. The analysis accounts for the effects of notch acuity, notch size, material and fatigue life on the fatigue notch factor kf. It opens the door to a new method for predicting fatigue life using two S–N curves for a given material; one being measured from a smooth specimen, the other from a severe V-notch.