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

Abstract

The influence of vehicle-track dynamic coupling on the fatigue failure of coil springs within the primary suspension of metro vehicles Steel coil springs are commonly used in the primary suspension of rail vehicles, usually in the form of two concentric springs. They exhibit strong internal resonances, which can lead to high vibration amplitudes within the spring itself. In some metro vehicles, large numbers of spring failures have occurred due to fatigue fracture in working conditions. 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 is used to determine the modal parameters of the primary suspension. The resulting dynamic stiffness matrix is then included in a multi-body vehicle model and coupled to a model of the track. This coupled model is used to investigate the effect of the dynamic properties of both the springs and the track on the stresses in the springs. 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 is found to correspond 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.

A mechanism for overcoming the effects of the internal resonances of coil springs on vibration transmissibility

“…The corresponding properties of the coil springs are listed in Table 2. The first fixed-fixed natural frequencies of the side-placed spring set are 51.9 Hz and 58.2 Hz [10], corresponding to modes of the outer and inner springs, whereas for the central spring set these are found around 80.8 and 97.0 Hz. Models representing the coil springs only by their static stiffness are also considered for comparison.…”

“…To include the dynamic effects of a coil spring, it is possible to use analytical methods [21] or numerical approaches such as the finite element method [10,22]. However, for simplicity, in this section a simple unidirectional model of an isolator with distributed mass is used [23].…”

“…At these frequencies both point and transfer stiffnesses have a peak, which for the assumed value of damping loss factor (0.01) is more than 100 times the static stiffness. This value of loss factor is greater than the actual damping of a metal coil spring but is chosen to approximate the effect of the rubber pad seen in [10].…”

“…Dylejko et al [8] studied the effects of internal resonances in machinery mounts on the noise radiation of ships. In other studies it has been shown that internal resonances of coil springs may also result in large amplitude vibration of the spring itself, leading to fatigue failure [9,10].…”

“…Usually, these are installed as two concentric springs in series with a rubber pad; the latter is intended to avoid excessive stiffening at the internal resonances [10]. Also for freight vehicles, various different primary suspension designs are used, many of which also contain coil springs [16].…”