Effect of Step Shapes on Fatigue Strength of Fitted Portions of Railway Axle

Fitted portions of railway axle have various shapes to establish adequate configurations with wheel, bearing and gear apparatus. Their dimensions are arranged by taking into consideration of fretting fatigue in accordance with the design standard of railway axles in Japan. There is, however, no guideline for proper shapes in the standard in spite of that the fatigue strength would depend on the fitting shapes. The objective of the present study is to develop an evaluation method of the fretting fatigue strength, which can be used in rational axle design to arrange the shapes of fitted portions. The present paper, as a beginning report of the study, firstly shows outline of the evaluation method, and then introduces detail contents of fatigue strength of non-step fitting and effect of step shape, where the fatigue data in literatures are systematically analyzed into regressed formulation. As a result, it is concluded that the fatigue strength of non-step fitting is influenced by load transmit type and stiffness parameter and that effect of step shape can be estimated by the combination of step ratio and contact angle. And finally finite element analyses are performed in order to investigate a reason of fatigue strength variation in non-step fitting. It is clarified that the axial stress amplitude at the fitting edge is considerably increasing in case of load transmit collar and large stiffness parameter.