The Effect of High Tensile Pre-load on Rotating Bending Fatigue Strength of Carbon Steel

Abstract

High load levels are sometimes observed in randomly varying loads applied to some structures or machine parts, owing to sudden accidents or some other causes. Recently, furthermore, materials are being used under severe loading conditions and often subjected to stresses comparable to the range. In case of designing, it is dangerous to neglect such high load levels.
The purpose of the present study is to investigate the effect of high tensile loads (in plastic range) on rotating bending fatigue strength of carbon steel. In this paper, as the first step, in order to obtain the fundamental data, the fatigue tests were carried out on smooth specimens of 0.33%C carbon steel subjected to a static high tensile load prior to stress cycling. The results were discussed on the basis of hardness change, residual stress change, surface observation during the fatigue tests and the effect of heat treatments.
The conclusions obtained are summarized as follows:
(1) In many cases, the tensile pre-load lowers the rotating bending fatigue strength. Especially, in the case of the lower yield point pre-load, the decrease of fatigue strength is more pronounced and in the case of the highest pre-load just under the tensile strength, the fatigue strength increases slightly above that of a virgin specimen.
(2) As the reasons of change in fatigue strength by the tensile pre-load, it is necessary to consider the stress concentration due to non-uniformity of work hardening as well as the residual stress and work hardening.
(3) By the heat treatments after pre-load, the fatigue strength of pre-loaded specimens increases, because the annealing effect by the heat treatment reduces the stress concentration due to non-uniformity of work hardening.