Impact forces at dipped rail joints

Impact forces develop at the wheel/rail interface due to the presence of defects in the running surface of the wheel and/or the railhead. This paper reports on wheel impacts, caused by permanently dipped rail joints, that are characterised by high-frequency impact forces generated by high amplifications of the static load that occur for a very short duration (P₁ forces), followed by relatively low frequency, lower amplitude forces (P₂ forces) that occur for a longer duration. These impact forces are affected by the design of components adjacent to the wheel and rail, namely the bogie’s primary suspension and rail seat pads; the influences of stiffness and damping characteristics of these components are investigated. A modified three-dimensional simulation model of the dynamics of the wagon/track system that includes defects in the track is created and is used to obtain the time series of the impact force. This is converted into impact force factors that are compared with a set of field-measured data reported in the literature. A simplified equation for the determination of impact force factors due to dipped rail joints is also proposed and validated.