Thermal analysis and fatigue verification of the LWR for an effective maintenance of the railway transport network

The increase in trains velocity and the improvement of comfort on railways belong to both the improvement of vehicles performances and to the use of the long welded rail (LWR). The analysis of the thermal set-up of the track is fundamental for the sake of the railway transport network performances: it basically deals with the changes in spans and strains occurring daily after temperature ranges. This phenomenon is described by the free dilatation law for tracks without bonds and by the stopped dilatation law for completely constrained tracks. The thermal analysis of the LWR shows a cyclic soliciting phenomenon belonging to both the daily temperature ranges and to the effects of moving vehicles: from this point of view a repetition of strains which involves an appropriate fatigue verification of the railways can be identified. For this reason the authors propose a procedure based on the synergic application of the Woehler construction theory for the fatigue curves and of the Miner law of linear accumulation. Once the Woehler curves are found as function of the different stress state due to the thermal variations and to the moving vehicles passing, the comprehensive damage for both kinds of strains can be quantified by means of the Miner theory. For this purpose the authors propose the implementation of a calculation software which can automate the thermal lay-out analysis phase, performing the Woehler curve, the internal stresses computation and the damage analysis following Miner’s law. In conclusion, this research is an useful tool for an effective maintenance of the LWR, as it allows the monitoring of the stress state of tracks, especially during the last part of their life cycle, when the temperature range and the moving vehicles passage consequences are more severe.