Pingbo Wu

Effects of structure elastic deformations of wheelset and track on creep forces of wheel/rail in rolling contact

Abstract In this paper the mechanism of effects of structure elastic deformations of bodies in rolling contact on rolling contact performance is briefly analyzed. Effects of structure deformations of wheelset and track on the creep forces of wheel and rail are investigated in detail. General structure elastic deformations of wheelset and track are previously analyzed with finite element method, and the relations, which express the structure elastic deformations and the corresponding loads in the rolling direction and the lateral direction of wheelset, respectively, are obtained. Using the relations, we calculate the influence coefficients of tangent contact of wheel and rail. The influence coefficients stand for the occurring of the structure elastic deformations due to the traction of unit density on a small rectangular area in the contact area of wheel/rail. They are used to revise some of the influence coefficients obtained with the formula of Bossinesq and Cerruti in Kalker’s theory of three-dimensional elastic bodies in rolling contact with non-Hertzian form. In the analysis of the creep forces, the modified theory of Kalker is employed. The numerical results obtained show a great influence exerted by structure elastic deformations of wheelset and track upon the creep forces.

The study of post-derailment measures to limit the extent of a derailment

Preventing railway vehicles from derailing is an important issue for the rail industry. Also important is minimizing the outcome of a derailment by formulating post-derailment measures to limit the extent to which railway vehicles deviate from the track. In this paper, two kinds of post-derailment devices are designed and then validated using derailment experiments performed in the laboratory. The derailment experiments are performed on a derailment test bench designed by the Traction Power State Key Laboratory. To design the\ post-derailment devices, a half-car derailment test without any post-derailment device is conducted to understand the dynamic behaviour after a derailment. Then devices that can be mounted under the axle box to limit the lateral displacement of the vehicle during the derailment are designed on the basis of the observed dynamic behaviour. A theoretical analysis is used to derive the relationship between the mounting position and the initial conditions of the derailment. Finally, the two devices, which have different mounting positions, were verified in derailment experiments. The verification results indicate that a device with a reasonable mounting position can limit the lateral displacement of the vehicle and reduce the consequences of a derailment. Also, in order to avoid the fastener area, the distance between the device and the wheel needs to be larger than 180 mm.

Estimation of the damping effects of suspension systems on railway vehicles using wedge tests

The damping ratios of suspension systems on a railway vehicle were estimated in terms of the free-decay responses obtained by applying the logarithmic-decrement method to data obtained in wedge tests. The characteristics of the free-decay responses were measured both for motor and trailer cars experiencing either the tare loading (AW0) or crush loading (AW3) condition and either inflated or deflated air springs. The considered cases included bouncing, pitching, rolling and lateral motions. A dynamic model was established and the simulation results were compared with the experimental results. For the vertical cases, the time cycles and displacement amplitudes of the free-decay response are related to the state of the air springs and the vehicle load. The damping ratio of the secondary suspension for inflated air springs is about three to five times higher than for when the air springs are deflated. For the primary suspension, it is two to four times higher. Also the heavier the carbody loads, the much more severe is the divergence. Furthermore, the damping ratios have their largest values for the pitching modes, followed by the bouncing modes and finally the rolling modes. For the lateral cases, the free-decay responses have similar characteristics to those of the vertical responses but with smaller amplitudes. All the tests show good agreement with one another, and the primary and secondary suspensions show similar regularities. The simulations show a good agreement with the test results and highlight that the initial velocity has only a limited effect on the test results.

Post-derailment dynamic behavior of railway vehicles travelling on a railway bridge during an earthquake

This study developed a post-derailment dynamic model of railway vehicles to investigate their post-derailment dynamic behavior when travelling on a railway bridge during an earthquake. The model is composed of three parts: multi-body dynamic model of the railway vehicle, a collision detection model, and a contact force model. The dynamic model considered all the various kinds of contacts that may occur during the derailment, such as wheel/track slab contacts, wheel/fastener contacts, and brake-disc/rail contacts. A collision detection model that was based on the tight-fitting oriented bounding box trees approach was adopted to detect the collision situations during the derailment. The contact force model was used to calculate the contact force based on a Hertz spring-damper and the Coulomb friction law. Using this model, the post-derailment dynamic behavior of railway vehicles travelling on a railway bridge experiencing earthquake excitations was investigated. First, a seismic response analysis of the railway bridge was conducted in order to obtain the seismic response of the railway bridge; it was subsequently used as the input to the post-derailment dynamic model. Then the derailment postures of the vehicle and contact situations were fully analyzed to understand the post-derailment dynamic behavior of railway vehicles during the earthquake. The obtained results show that the brake disc adopted in the model has the ability to limit the deviation of the wheelsets after the derailment.

Field measurements of the evolution of wheel wear and vehicle dynamics for high-speed trains

ABSTRACT This investigation demonstrates the wheel wear evolution and related vehicle dynamics of high-speed trains with an operating distance (OD) of around two million kilometres. A long-term experimental test lasting two years was conducted to record the wheel profiles and structural vibrations of various trainsets. The wheel wear, namely the profile shape, worn distribution and wheelset conicity, is investigated for several continuous reprofiling cycles. Typical results are illustrated for the stability analysis, and the ride quality is examined with increasing OD. In addition, the vibration transition characteristics between suspensions are investigated in both the time and frequency domains. The experiments show that the dominant wear concentrates on the nominal rolling radius, and the wear rate increases with OD because of the surface softening resulting from the loss of wheel material. The vibration of structural components is aggravated by the increase of the equivalent conicity of the wheelset, which rises approximately linearly with the wheel wear and OD. High-frequency vibrations arise in the bogie and car body related to the track arrangement and wheel out-of-roundness, causing the ride comfort to worsen significantly. Additionally, the system vibration characteristics are strongly dependent on the atmospheric temperature. Summaries and conclusions are obtained regarding the wheel wear and related vehicle dynamics of high-speed trains over long operating times and distances.

A study of polygonal wheel wear through a field test programme

ABSTRACT High magnitude impact loads caused by polygonal wear of the wheels have been associated with in-service failures of structural components of high-speed railways, although the mechanisms leading to wheels’ polygonalisation is not yet fully understood. In this study, a long-term field test programme is undertaken and the data are analysed to gain better understanding of the growth in polygonal wear, and its characteristics and correlation with the axle box acceleration. The field measurements on a high-speed railway involved monitoring of wheels profiles between successive re-profiling of the wheels so as to identify the rate of growth of wear in addition to the axle box acceleration. The data suggested rapid growth in wheel wear, which could be characterised by polygonal wear of nearly 18th and 19th harmonic order. It is further shown that the magnitude of axle box acceleration increased considerably with increasing wear magnitude of the wheel.