Plain–fretting fatigue competition and prediction in spline shaft-hub connection

The dynamically loaded spline shaft-hub connection that without macro relative movement between shaft and hub are exposed to the danger of fretting fatigue in the contact zone of teeth flank and plain fatigue at teeth fillet at the same time. The competition of fretting fatigue and plain fatigue determines that which one dominates the failure of it and therefore the fatigue performance of it. In order to deal with this plain–fretting fatigue coexisted situation, a plain–fretting fatigue unified prediction model is introduced in this paper and implemented in the representative spline teeth pair. Predicted by this model, the failure of involute spline shaft-hub connection teeth DIN 5480 45 × 2 × 21 is plain fatigue at teeth fillet dominated. Corresponding to the theoretical modeling efforts, a representative teeth pair fatigue test apparatus was developed. With this test apparatus, the initiation and propagation of fatigue cracks can be detected on line by monitoring the change of resonant frequency. The test results also showed that the crack occurs at teeth fillet at first.