Wheel rail contact conditions causing rail squats

The development of squat defects has become a major concern in numerous railway systems throughout the world. The paper details findings from vehicle dynamic simulation and contact patch calculations for an example case of a curve transition. The example case is drawn from operations on the Sydney metropolitan and interurban areas and the simulation results are cross compared to observations of squat formation in RailCorp track.Observed squats occur in curve transition of tight curves and in medium radius curves on the high rail. Squats locations and numbers of squats are more numerous with locations on uphill grades or exiting stations, locations where traction effort is applied. The curve locations in RailCorp produce cracks initiating as head checks in the gauge corner of the rail with a squat crack being produced from the middle of the rail head growing both laterally to the field side of the rail and longitudinal in both directions.The vehhicle dynamics simulations show that risk of RCF formation based on the creep energy T is greatly dependent on tractive effort in curving. There are distinctly different contact force conditions generated by the leading and trailing wheelsets of the bogie. The squat crack growth occurs largely under the contact patch of the trailing wheel whilst head checks occur with the leading wheelset contact patch.