Abstract This paper presents a methodology to study the fatigue strength of shafts under repeated impacts. The equipment for repeated impacts was designed for torsion tests of shafts for the same loading conditions as in service. The stress concentration effect, due to a fillet radius between square and circular cross-sections of the axle, was emphasized. Five groups of shafts with radius between 0.5 and 3.2 mm from a number of 100 shafts with different notch radius were selected. Based on a model proposed by the authors for defining the energy reduction factor β due to a notch the variation of the notch sensitivity factor η versus fillet radius was analyzed for two different numbers of cycles. It was observed that for a high number of cycles (N=2×106 impacts) the behaviour is similar to that of traditional fatigue tests. Oppositely, at lower number of cycles the particular aspect of the notch sensitivity is highlighted in the limited durability domain.