Abstract
In the two previous papers, the authors discussed the effect of a single high tensile load applied prior to stress cycling or during stress cycling on fatigue strength. In the present study, the effect of periodic high tensile loads on the rotating bending fatigue strength of 0.33% carbon steel were investigated.
The main conclusions obtained are summarized as follows:
(1) In the case of the high tensile load σH=39.5kg/mm2 corresponding to the lower yield point of virgin specimen, the S-N curve bends slightly to the side of shorter life at the stress near the fatigue limit of virgin specimen.
(2) In the case of the high tensile load σH=60.0kg/mm2 corresponding to 8.7% true strain of virgin specimen, the fatigue life is shorter than that of σH=39.5kg/mm2 and the S-N curve bends abruptly to the side of shorter life at the stress near the fatigue limit of virgin specimen.
(3) The effects of frequency and sequence of high tensile loads are not found.
(4) In the case of the high tensile load σH=39.5kg/mm2, the fracture surface of specimens exhibits fatigue fracture surface, while in the case of σH=60.0kg/mm2 it shows fatigue fracture surface above the S-N diagram's nose but local contraction fracture surface below that point.
(5) In most cases the values of the cumulative cycle ratio are very small.
