The influence of the non-linear stiffness behaviour of rail pads on the track component of rolling noise

The stiffness of the rail pad is a critical parameter in determining the no ise from the track. Both theoretical and experimental studies show that a s tiff pad, by coupling the rail to the sleeper, leads to a high attenuation of rail vibration with distance along the track and an increase in the slee per vibration. In this way the rail-radiated component of noise is reduced but the sleeper component is increased. Conversely a soft pad leads to a lo w sleeper noise component but greater rail noise, as the rail can vibrate o ver a greater length. In modern track, soft pads are used, as they lead to reduced track forces and less damage to track components such as sleepers. In this paper, measured vibration characteristics of track are presented an d compared with predictions. A recent study of the effect of the load depen dence of the rail pad and ballast stiffnesses on the dynamic behaviour of t he track is extended to give a practical assessment of the effects on the n oise radiation. It is shown that, for a typical soft pad with a high load d ependence, neglect of the preloading effect would lead to a significant ove rprediction of the track noise component. It is thus shown that soft pads n eed not be so disadvantageous for noise as has been suggested.