Modelling of curve breathing in tight curves

Abstract

Present work aims to investigate the deformation behaviour of continuously welded rail (CWR) tracks of both meter and normal gauge railways in tight curves, exposed to thermal loading. The high axial forces in the rail due to restricted thermal expansion lead to lateral displacements of the track panel. This so- called curve breathing is officially tolerated for meter-gauge railways, but not for normal-gauge infrastructure. However, the empirical knowledge about the real behaviour of curve breathing is low. The crucial condition for the tolerance of curve breathing is that the deformation and the process itself must be uniform. Track alignment defects have a negative impact on comfort, durability, and maintenance of both rolling stock and infrastructure. In a worst case scenario, this could even have a negative influence on safety, when several wave-shaped track alignment defects lead to a dynamic stimulation of the vehicle resonance frequency. Rod-sleeper tracks show non-uniform deformations, with sleepers moving 20 mm in close distance to sleepers which don’t move, behaving like fixed points. On the contrary, the curve breathing of a track panel with Y-shaped sleepers is much more uniform. No local fixed points can be identified. This leads to the conclusion that depending on the track stiffness, the lateral displacement behaviour is different. The track stiffness can be influenced by the sleeper type (Y-shaped steel sleepers, frame sleepers). In this paper, analytical (force method) and numerical (FEM) simulations are used to reproduce the differing behaviour of track panels with diverging stiffness. As input parameters, empirically measured values for the lateral ballast resistance are used. The obtained results are cross-compared with the measured displacements, and are in agreement. The model is used to perform parametric studies and to investigate possible solutions to the problem. It is concluded that the maximum value of the lateral displacement depends on the lateral displacement resistance. Nevertheless, the shape of the deformation is influenced mainly by the track stiffness. A high track panel stiffness equalizes the variation of the lateral displacement resistance. In summary, it can be said that, for a high track alignment quality it needs a high lateral ballast resistance or a high track stiffness, depending on the radius of the curve. Their individual effects and their interactions are investigated in this paper.