Root cause analysis of locomotive wheel tread polygonisation

Abstract Periodic out-of-round or polygonised wheels were detected on a fleet of high adhesion locomotives operating within South Africa. The polygonised wheels increased the vertical load spectrum of the locomotive resulting in accelerated component failures. During the initial investigation it was found that torsional axle vibration could lead to the polygonisation of the wheels. The torsional vibration of the locomotive axle was confirmed theoretically and experimentally through various physics models and on-track measurements. Based on the results, two potential torsional vibration excitation mechanisms were identified. A link was also established between the torsional vibration frequency, vehicle operating speed and the polygonisation order. Based on the similarities of the two excitation mechanisms a vibration suppression system was considered and tested. A reduction in the torsional vibration amplitude was observed when the suppression system was active.