The influence of vehicle–track dynamic coupling on the fatigue failure of coil springs within the primary suspension of metro vehicles

In some metro vehicles, large numbers of failures of coil springs in the primary suspension have occurred due to fatigue fracture. The cause of these failures is investigated by studying the vehicle/track interaction, the modal response of the coil springs and the stresses occurring within them in working conditions. A finite element model of the primary suspension is used to determine the dynamic stiffness matrix, which is then included in a multi-body model of the vehicle and coupled to the track. The springs exhibit strong internal resonances at around 50–60 Hz, at which very large stresses occur in both springs. This frequency range coincides with the P2 resonance frequency (wheelset mass bouncing on the track stiffness) for the standard slab track system used on this metro system. For other track systems, the P2 resonance occurs at a different frequency and the stresses are lower. These results are confirmed with field test data. From the stresses the weakest position in the inner spring is identified, which corresponds to the position of common breakages found in field observations. Some guidelines are proposed for reducing the vibration and stress, so that the fatigue fracture incidents can be reduced.