The steady state forces and moments on a railway wheelset including flange contact conditions.
2015-03-13T09:08:49Z (GMT) by
Railway vehicles are fitted with coned wheels to provide a measure of stability, but it can be shown that since the forces between wheel and track are non-conservative, dynamic instability occurs at a certain critical speed. Under these conditions the wheelsets sway from side-to-side of the, track with the flanges of the wheels contacting the rails. This can lead to derailment when the wheel climbs up the rail and eventually jumps off. The forces which exist between wheel and rail are due to the phenomenon known as "creepage", and various theories exist which predict these forces in the plane of the contact area. An investigation has been carried out into these theories with the railway wheelset problem in view, particularly the flange contact case. It is possible, by assuming small displacements which avoid flange contact, to carry out a linearised study of the lateral dynamics of a wheelset, but the presence of the wheel flanges introduces a nonlinearity into the problem. A mathematical model of a wheelset and track has been defined based on real wheels with a "worn" tyre profile and real track. Computer programs have been written which calculate the contact points when the wheelset is displaced laterally and yawed by various amounts, including flange ,contact conditions. Up to three contact points can exist between the wheelset, and track. Forces in the contact areas have been calculated using the various theories assuming the wheelset to be rolling along the track a ta constant velocity in a displaced position. These forces have been manipulated to give the total forces and, moments on the wheelset and are presented for various vertical load distributions and for various angular and lateral displacements of the wheelset from its central position. Although theories exist which predict the forces for flange type contact, i. e. very elongated contact ellipse with a large amount of spin present, it became apparent during the course of the investigation that very little experimental evidence was available for such conditions. As a result a roller rig was built to provide this data, and measurements were made of· the lateral force due to various amounts of lateral creep and spin on elongated contact ellipses. Results from these tests have been compared with the available theories and show reasonable agreement.