Rail Corrugation Growth on Curves
Doktorsavhandling, 2012

The development of periodic irregularities with distinct wavelengths (corrugation) on the low rail of small radius curves is studied through mathematical modelling, numerical simulations, field measurements and laboratory investigations. One year of monitoring of roughness on the low rail of a 120 m radius curve on the metro of Stockholm Public Transport (SL) showed severe growth of rail corrugation with wavelengths of about 5 cm and 8 cm. About 300 days after rail grinding, the corrugation was observed to reach a constant amplitude. Based on a section removed from the corrugated rail, a laboratory investigation showed plastic deformation in the lateral direction towards the field side. No significant difference in microstructure was found when corrugation troughs and peaks were compared. A time-domain model for the prediction of long-term roughness growth on curves has been developed and validated versus field measurements. The simulation model is able to simultaneously capture the low-frequency vehicle dynamics due to curving and the high-frequency dynamics due to excitation by for example short-pitch corrugation. Non-Hertzian and non-steady effects in the wheel‒rail contact are considered. Simulations show that the short-pitch corrugation on the small radius curve at SL is generated by wear induced by the leading wheelset of passing bogies. The corrugation wavelengths 5 cm and 8 cm are determined by the excitation of the first antisymmetric and first symmetric bending eigenmodes of the wheelset, respectively. The importance of accounting for the phase difference between the calculated wear and the present rail irregularity in predictions of corrugation growth is demonstrated. Due to a phase difference approaching a low constant value, the growth of corrugation is predicted to eventually develop into a stationary state where it is translated along the rail with a constant amplitude. For track geometry and traffic conditions corresponding to the selected curve at SL, simulations indicate the wheel–rail friction coefficient to have a significant influence on corrugation growth. For friction coefficient 0.6 (measured at dry contact conditions), corrugation growth is predicted at several wavelengths whereas for friction coefficient 0.3 (due to application of a friction modifier) it is shown that an initial rail irregularity is gradually worn off by passing traffic. Based on a new set of field measurements in the same curve (another year of monitoring), it was shown that the application of a friction modifier directly after grinding is an effective mitigation measure to prevent the development of rail corrugation.

short-pitch rail corrugation

rotating flexible wheelset model

small radius curves

prediction of long-term roughness growth

plastic deformation

non-Hertzian and non-steady wheel‒rail contact

wear

rutting corrugation

HA3
Opponent: Dr Stuart Grassie

Författare

Peter Torstensson

Chalmers, Tillämpad mekanik, Dynamik

Korrugering (vågbildning) på kontaktytan av innerrälen i snäva kurvor är ett vanligt förekommande problem på tunnelbanespårsystem världen över. Detta orsakar förhöjda dynamiska krafter i kontakten mellan hjul och innerräl, vilket i sin tur bidrar till ökad bullergenerering och i allvarliga fall även till skador på spår- och vagnskomponenter. Regelbundna klagomål framförs till Stockholms Lokaltrafik (SL) angående bullergenerering från en specifik tunnelbanekurva med kurvradie 120 m. För att motverka korrugeringen i kurvan måste SL slipa rälen med årsintervaller. Den här åtgärden förhindrar dock inte återväxten av korrugering och den utgör därför ingen tillfredställande långsiktig lösning på problemet. Matematiska modeller erbjuder möjligheter att bättre förstå de medverkande mekanismerna bakom generering av korrugering och kan på så sätt bidra till dess lösning. Denna avhandling studerar rälkorrugeringstillväxt i kurvor genom numeriska simuleringar, fältmätningar samt laboratorieundersökningar. En beräkningsmodell har utvecklats vilken associerar korrugeringsbildningen i den snäva kurvan på SLs tunnelbana till nötning genererat av det ledande hjulparet i passerande boggier. Vidare har både numeriska simuleringar och fältförsök demonstrerat att applicering av en så kallad friktionsmodifierare på innerrälens kontaktyta är en effektiv åtgärd för att förhindra återväxten av korrugering efter rälslipning.

The development of corrugation (a periodic waviness on the running surface) on the low (inner) rail in curves is a problem common for the majority of metro track networks worldwide. High dynamic forces created in the contact between the wheel and the corrugated low rail lead to generation of noise and vibration and in severe cases to damage of track and vehicle components. Complaints regarding noise regularly reach Stockholm Public Transport (SL) from passengers and people living close to a specific 120 m radius curve on their metro track network. To manage the problem SL performs annual rail grinding, but this has no potential of preventing corrugation to reappear and is not a satisfying solution. A deeper understanding of the mechanisms generating the corrugation can be achieved by mathematical modelling and this could contribute to finding a design solution to the problem. This thesis studies the development of corrugation on the low rail of curves through numerical simulations, field measurements and laboratory investigations. A mathematical model for the prediction of corrugation growth on curves has been developed. Numerical simulations show the corrugation development on the small radius curve on the metro of SL to be generated by the leading wheelset in passing bogies. Further, both simulations and field measurements demonstrate that the application of a friction modifier on the surface of the low rail directly after grinding can prevent corrugation to reappear.

Ämneskategorier

Maskinteknik

Farkostteknik

Drivkrafter

Hållbar utveckling

Styrkeområden

Transport

Building Futures

ISBN

978-91-7385-758-1

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 0346

HA3

Opponent: Dr Stuart Grassie