The effects of track non-linearity on wheel/rail impact

Wheel/track impact due to rail joints or wheel flats has been studied over many years. The railway track is usually assumed to be linear in order to simplify the track model, although the rail pad and ballast are actually non-linear. This may cause incorrect results to some extent in some circumstances, as the pad and ballast stiffness varies with load. In this paper wheel/track impact is studied using a non-linear track model. The rail is represented by a finite element (FE) model and is supported by a non-linear track foundation. Wheel/track impacts are simulated at different train speeds and three types of rail pad, soft, medium and stiff, are used in the simulations. It is shown that the impact forces rise dramatically when the stiff rail pads are used. On the other hand, using soft pads can reduce impact forces significantly. Compared with the results from the linear track model, both the impact force and the track vibration level are shown to be noticeably higher from the nonlinear track than those from the linear track. It is therefore concluded that linear track models are not appropriate for wheel/track impact because the track foundation stiffness varies dramatically under the impact force.