抄録
Conducting the rotating bending fatigue test of mild steel specimens with a drilled hole of various size, we studied on bad influences exerted owing to the hole, and the others connected with it. The specimens are 12mm in diameter, 25mm in parallel length, and each hole drilled on them is 1, 2 and 3mm in diameter, and at intervals of 1mm from 1 to 12mm in depth.
The results obtained through our experiments are as follows:
(1) When the shafts with a hole of the same diameter and various depth are subjected to a rotating bending load, according as the hole depth increases, up to about 3mm in depth, the nominal fatigue limit σwn falls rapidly, and from about 4 to 8mm in depth, its lowering becomes very slow, and above about 9mm in depth, it becomes great again.
(2) In every size of hole, the fatigue limits σwk calculated on the cross section containing a hole axis are within the range of 15-18kg/mm2, accordingly notch factor β is about 1.2-1.3. In Fig. 6 is shown an useful diagram for the design of shafts with hole to be subjected to the rotating bending load.
(3) When the shafts mentioned in (1) are subjected to the heavy load over fatigue limit, according as the hole depth increases, up to about 3mm hole in depth, the fatigue life is shortened at a great rate, and over about 3mm in depth, its lowering becomes very slow, especially for the shafts with a hole 1mm in diameter.
(4) In every size of hole, the starting point of the way to fatigue is always on either side of entrance of the hole, and so the fatigue limits are raised to some extent owing to hardening of this parts by shot-peening and others.
