Abstract
In this paper, the effects of forms of stress waves on the fatigue strength are investigated, using three low carbon steels. The forms of stress waves adopted are sinusoidal and nonsinusoidal ones.
The fatigue tests were made in plane bending and torsion under completely and partly reversed stresses. The testing machines used were the Upton-Lewis plane bending fatigue testing machine and the Upton-Lewis torsion fatigue testing machine. The eccentric mechanisms of these machines were modified so that they might produce expected forms of stress waves. The driving speed was 100 to 200cpm.
The test results were: (1) the fatigue lives at the cyclic nonsinusoidal waves, shown in Fig. 1, seem to be about the same as those at the cyclic sinusoidal waves, (2) the fatigue lives at the cyclic twin waves, shown in Fig. 2, are different from those at the cyclic sinusoidal waves, that is, the secondary wave in the twin wave has an effect on the fatigue life depending on the stress magnitude, and (3) the changes of the stress amplitude in the process of fatigue were similar for the all forms of cyclic stress waves under the constant strain amplitude.
