Influence of compressive pre-strain on tensile fatigue life in carbon steel S45C

For S45C carbon steel with three heat treatments, pulsating tension tests were carried out under controlled stress condition. The effect of compressive pre-strain, Bauschinger effect and controlling factors on fatigue life were examined. The following results were obtained. The decrease of pulsating fatigue life was caused by three factors, i.e. increase of the total plastic strain amplitude, cyclic plastic strain amplitude and cyclic creep rate. The increase of Bauschinger strain led to the increase of the value of the three factors. Then it resulted in shorter fatigue life. In order to examine the cyclic stress conditions to the fatigue life, the stress ratio was defined as the ratio of maximum cyclic stress to yield stress of each material. Bauschinger strain was occurred when the stress ratio was under the threshold for each material. As the result, cyclic plastic strain amplitude and cyclic creep rate were increased and then pulsating fatigue life was reduced.