Fatigue Strength of Cast Crankshafts

Abstract

The paper gives the results of a systematic investigation into the effects of the proportions of a cast crankshaft on its bending fatigue strength. A single-throw shaft of 4½ inches diameter was chosen as likely to give information useful to the builders of small stationary engines as well as automobile engines, and the different dimensions were varied one at a time over a range which covered the usual practical proportions. In addition, to obtain some information on a possible scale effect, tests on a geometrically similar shaft of 2¼ inches diameter were included. It is considered that, with a few exceptions which are indicated in the paper, most of the conclusions from these tests will apply equally to forged and cast crankshafts. The paper refers also to tests made on a number of different cast-iron and cast-steel crankshafts of the same design, to determine, from the point of view of fatigue strength, their merits as crankshaft materials, and to find out to what extent the fatigue strength of the finished crankshaft can be predicted from the usual mechanical tests on the materials.