Abstract
In this paper, the change of plastic strain amplitudes under the tension-compression double stress and the growth of the fatigue cracks under plain bending double stress were investigated on three carbon steels. In these tests the phenomena of plastic strain amplitude and growth of fatigue cracks under the secondary stress are entirely different from those under the primary stress only, i.e., the material which subjected to the primary stress has the different features from the virgin material. And it is thought that the advantage of fatigue under the secondary stress differs from that under the mono repeated stress. The effect of primary stress on the phenomena of material under the secondary stress does not die away till the specimen fractures.
