In order to investigate the statistical properties of fatigue strength of car-axle materials, the rotary bending fatigue tests have been carried out on smooth and press-fitted specimens made from the usual car-axle materials (SF55) and the actual car-axles.
From these test results, the effects of mechanical properties, chemical contents and size on the statistical property of fatigue stength were investigated. Also the effect of a period in service as actual car-axle was investigated. Also, the relation between P-S-N curve of small size specimens and that of actual car-axle was examined, and a method of estimating statistical property of full size parts using the data of small size specimens was discussed.
The main results obtained are as follows:
(1) Failure fatigue life under constant stress amplitude is influenced considerably by the mechanical properties and chemical contents such as tensile strength, yield point, Charpy impact value, hardness and Si content, but slightly by the other elements. Fatigue life varies in proportion to the above effective elements.
(2) The longer the period in service as actual car-axle, the shorter the failure fatigue life under constant stress amplitude is.
(3) The size effect on the statistical property of failure fatigue life is small.
(4) The statistical properties of fatigue life of small size press-fitted specimens are similar to those of full size car-axle.
