Abstract
F. S. (Fixed Stress) Typed Hysterograph is a torsion fatigue testing machine newly designed by the present writer. It is designed to be measurable the stress-strain diagram of the test piece which is stressed and vibrated by the speed of n=1, 900 rev/min. The mechanism of the hysterograph is very simple as shown in Fig. 1; it composes of the two plane mirrors m1 & m2 inclined both 45° to the axis and to each other. A point light reflected twice by the mirrors, describes on a plate glass the hysteresis loop of the test piece. The change in hysteresis loop of the test piece in the course of fatigue test is able to measure by this hysterograph. The accuracy of this apparatus is as follows: the hysteresis loop begins to appear when the plastic angle of twist θ=1' is introduced in the stress cycle. The mean stress τm=(τ0+τu)/2 is applicable by this machine besides the ordinary vibration ±τ stress. Duralumin, quenched and annealed, and Ni-Cr-W steel were tested. The results are shown in the fatigue diagrams in Figs. 6 and 12. Figs. 7 and 8 show the process of change of the hysteresis loops of duralumin, in which case hysteresis losses increase by fatigue. But Ni-Cr-W steel by this test fatigues and breaks under no hysteresis losses, as shown in Fig. 11. In the Ni-Cr-W steel, the test piece yields some permanent set θset, even in the fatigue limit, when the upperlimit-stress τ0 overcomes the elastic limit, in the case of mean stress applied. Fig. 16 shows the relation of permanent set between fatigue tests and static test. By these tests it is concluded that the θset of fatigue test is about half of the static. The fatigue limit, hysteresis loop and permanent set are measurable by our hysterograph.
