Polygonalization of railway wheels

Summary

A model of a flexible wheelset running on flexible rails is presented which demonstrates the growth of out-of-round profiles of the wheels. This process of growing is called polygonalization. We divide the model into two parts. One part describes the oscillations of the wheelset and the rails. The excitations, which are a result of the out-of-round wheels, are due to geometrical terms, while excitations of unsprung masses are not considered. The second part describes the development of the wheel profiles and the wear rate due to wear and hardening, respectively. The two parts can be coupled by means of perturbation theory with multiple-time scales, [4], [10] as a wear-feedback loop proposed in [6]. As the calculation show, the greater is the phase shift between the-out-of-round profiles of the right and the left wheel the faster the wheels become out-of-round. Furthermore, it is shown, that the first and the second bending modes of the wheelset play an important role in the growth of polygonized wheels. It should be emphasized that other reasons for polygonalization may exist too, e.g. excitations due to unsprung masses, [14].