ON THE FATIGUE TEST OF HOLLOW DRILL STEEL BY A FATIGUE-TESTING MACHINE OF ELECTROMAGNETIC-RESONANCE TYPE

Abstract

The authors investigated the fatigue strength of hollow drill steel rods under reversed bending, using an electromagnetic resonance type fatigue testing machine, as shown its block diagram in Fig. 1. 53 kinds of foreign and home manufactures are refered to the preparation of 10 kinds of test steels, whose chemical compositiong, physical and mechanical properties are listed in Table 1-2.
Results obtained were as follows;
1) Fatigue limits of hollow drill steel rods showed 20-30kg/mm2. Those were not affected by the kind of steel, but largely by their method or heat treatment. (Fig. 2)
2) Steels with the troostitic micro-structure, of hardness around Hv 400, couldobtain the maximum fatigue strength. (Fig. 3)
3) Surface conditions of hollow drill steel rods had a considerable influence on their fatigue strength.