Acoustical optimization of railpads by F.E. Modelling and validation by measurements

Noise emission is often influenced by resonance.In case of wheel-rail contact during train pass-by, the rail is excited at his resonance frequencies, e.g., the pinned-pinned resonance.The only component in contact with the rail that can dampen this resonance is the rail pad.It is known that, when changing railpad dynamic properties as stiffness and damping, the pass-by emission can be reduced significantly.Several projects in Europe show that railpad optimization in terms of stiffness and damping results in noise reduction of more than 3 dB compared to the standard soft pad, for passenger and freight trains at speeds between 80 and 160kph.The goal of this study is to further optimize the rail pad design, to keep the flexibility in the track for protection of sleepers and ballast, combined with a high TDR (Track Decay Rate), or rail vibrational damping.The focus lies on the optimization of the stiffness distribution over the railpad surface.It is shown that, for the same global vertical railpad stiffness, the TDR can be optimized in the pinned-pinned area.The optimization is first done in a frequency dependent F.E.M. (Finite Element Modelling), then optimized railpads are mounted in a track and noise emission is compared with non-surface optimized railpads.