Evaluation of fatigue crack propagation property on the wheelseat of normalized axles for narrow gauge line vehicles

In order to obtain a data to streamline the system including a method of flaw detection and its interval for normalized axles equipped with rolling stock running on existing narrow gauge lines, fatigue tests were conducted on normalized axles with artificial flaws of various depths and crack propagation property from artificial flaws was evaluated. The axles with semi-elliptical artificial flaws of depths from 0.5mm to 3mm at the wheelseat fractured at the inner end of press-fitted gear-side wheelseat adjacent to the stress relief groove of 1mm depth under cyclic nominal stress of 80MPa. Although some cracks initiated from the bottom of each artificial flaw, fretting fatigue cracks progressed to main cracks and led to the failure. On the other hand, as a test result on axle with same sizes of artificial flaws under cyclic nominal stress of 60MPa after 5.4 × 10 ⁷cycles, neither a prominent progressive crack from the artificial flaw nor the initiation of a fretting fatigue crack was observed. To discuss the above fatigue test results, the stress generated at the wheelseat during the fatigue test was analyzed by FEM, and then the stress intensity factor range was calculated with the analysis result. The evaluation results of crack propagation property by the calculated stress intensity factor range in view of fracture mechanics corresponded with the above test results.