This paper presents a detailed investigation conducted into the mechanism of the polygonal wear of metro train wheels through extensive experiments conducted at the sites. The purpose of the experimental investigation is to determine from where the resonant frequency that causes the polygonal wear of the metro train wheels originates. The experiments include the model tests of a vehicle and its parts and the tracks, the dynamic behaviour test of the vehicle in operation and the observation test of the polygonal wear development of the wheels. The tracks tested include the viaducts and the tunnel tracks. The structure model tests show that the average passing frequency of a polygonal wheel is approximately close to the first bending resonant frequency of the wheelset that is found by the wheelset model test and verified by the finite element analysis of the wheelset. Also, the dynamic behaviour test of the vehicle in operation indicates the main frequencies of the vertical acceleration vibration of the axle boxes, which are dominant in the vertical acceleration vibration of the axle boxes and close to the passing frequency of a polygonal wheel, which shows that the first bending resonant frequency of the wheelset is very exciting in the wheelset operation. The observation test of the polygonal wear development of the wheels indicates an increase in the rate of the polygonal wear of the wheels after their re-profiling. This paper also describes the dynamic models used for the metro vehicle coupled with the ballasted track and the slab track to analyse the effect of the polygonal wear of the wheels on the wheel/rail normal forces.

In particular locations of the railway track, the excessively polished rail in the inner corner and the large rail cant will lead to an extremely low wheel–rail contact conicity. Consequently, the carbody hunting instability arises and deteriorates the ride comfort of passengers. In this paper, the carbody hunting instability of an electric locomotive is observed and tested. Combined with the analysis of wheel–rail contact and track condition, the ride comfort and running stability indices are evaluated. The dynamic model for the locomotive is established. The measured wheel and rail profiles as well as the curve radius and superelevation are integrated into the simulation model to reproduce the phenomenon that the carbody hunting displayed violent in the straight line while the abnormal vibration disappeared in the curve segment. The linearised and non-linear study on the optimisation of suspension parameters are carried out to solve the carbody hunting instability. Finally, the optimised measures that decreasing the series stiffness and damping of the yaw damper as well as the primary longitudinal stiffness are put forward, and verified by the on-track test. The investigation enriches the study of carbody hunting instability and gives some ideas to probably solve the abnormal vibration.