Effect of Overstressing on Fatigue Limit of Low Carbon Steel under Rotating Bending and Torsion

Abstract

The main objectives of the present study are to investigate the effect of overstressing on fatigue limit and then to make clear the effect of strain aging in such case.
For these purposes, by using two kinds of low carbon steels, Al-killed and rimmed steel having different strain-aging abilities, fatigue tests were carried out under rotating bending and torsion. The slip line and crack initiation curves, as well as the S-N curves, and the damage curves were drawn for each case. The variations of hardness and temperature on the surface of the specimens during stress cycling were measured.
The most important result obtained from these experiments is that the damage curve for the rimmed steel with higher strain-aging ability lies relatively in the side of shorter life as compared with that of the Al-killed steel with lower strain-aging ability. Therefore, it seems that the strain aging during stress cycling is not effective to the damage on fatigue limit caused by overstressing.