Zefeng Wen

Effect of Disabled Fastening Systems and Ballast on Vehicle Derailment

The effect of disabled fastening systems and ballast on railway vehicle derailment is investigated by developing a nonsymmetrical coupled vehicle/track model. In the model a half passenger car is considered, and modeled with a multi-body system with 18 degrees of freedom, which runs on a tangent track at a constant speed. The tangent track is modeled as two elastic beams by discrete nonsymmetrical supporters modeling fastening systems, sleepers, and ballasts. The normal contact forces between wheels and rails are described by Hertzian elastic contact theory, and the tangential forces by the nonlinear creep theory of Shen et al. (Proceedings of the 8th IAVSD Symposium, Cambridge, MA, pp. 591-605). In the numerical analysis, the disabled rail fastening, rail pad, and ballast, on one and two sides of the track are, respectively, considered. Through a detailed analysis, derailment coefficients and the track state variations are obtained. The derailment coefficients are defined as the ratio of the lateral force to the vertical force of the wheel and rail (indicated by L/V), duration of L/V, and rate of the wheel load reduction (indicated by AVIV), respectively. The variations of the contact points on the wheel treads, the track gauge, the track cross-level, and rail turnover angle are present in the paper. The numerical results obtained indicate that the failure of rail supports has a great influence on the vehicle running safety.

Adhesion Experiment on a Wheel/Rail System and Its Numerical Analysis

Abstract The experiment on the adhesion coefficient of a wheel-rail system has been carried out by means of a full-scale test facility under the condition of different axle loads and rolling speeds. The effects of the condition of the wheel-rail contact surfaces, such as a clean and dry surface, water and oil contamination and slip, on the adhesion coefficient have been investigated in the experiment. The experimental results show that, when the rolling speed of the wheelset increases, the adhesion coefficient decreases under the condition of the constant creepage and water contamination on the contact surfaces, but it increases for oil contamination. Using the data obtained by statistics and analysis of the experimental results and Kalkers rolling contact theory with Hertzian form modified by the present authors, a numerical analysis concerning the effect of wheelset rolling speed on the adhesion coefficient and the distribution of the stick-slip area in the contact area has been made. The numerical results are in good agreement with those obtained by experiment. They are very useful in designing the traction power of a locomotive at higher speeds.

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.

A study on high-speed rolling contact between a wheel and a contaminated rail

A 3-D explicit finite element model is developed to investigate the transient wheel–rail rolling contact in the presence of rail contamination or short low adhesion zones (LAZs). A transient analysis is required because the wheel passes by a short LAZ very quickly, especially at high speeds. A surface-to-surface contact algorithm (by the penalty method) is employed to solve the frictional rolling contact between the wheel and the rail meshed by solid elements. The LAZ is simulated by a varying coefficient of friction along the rail. Different traction efforts and action of the traction control system triggered by the LAZ are simulated by applying a time-dependent driving torque to the wheel axle. Structural flexibilities of the vehicle–track system are considered properly. Analysis focuses on the contact forces, creepage, contact stresses and the derived frictional work and plastic deformation. It is found that the longitudinal contact force and the maximum surface shear stress in the contact patch become obviously lower in the LAZ and much higher as the wheel re-enters the dry rail section. Consequently, a higher wear rate and larger plastic flow are expected at the location where the dry contact starts to be rebuilt. In other words, contact surface damages such as wheel flats and rail burns may come into being because of the LAZ. Length of the LAZ, the traction level, etc. are varied. The results also show that local contact surface damages may still occur as the traction control system acts.

Elastic-Plastic Finite Element Analysis of Nonsteady State Partial Slip Wheel-Rail Rolling Contact

A finite element analysis with the implementation of an advanced cyclic plasticity theory was conducted to study the elastic-plastic deformation under the nonsteady state rolling contact between a wheel and a rail. The consideration of nonsteady state rolling contact was restricted to a harmonic variation of the wheel-rail normal contact force. The normal contact pressure was idealized as the Hertzian distribution, and the tangential force presented by Carter was used. Detailed rolling contact stresses and strains were obtained for repeated rolling contact. The harmonic variation of the normal (vertical) contact force results in a wavy rolling contact surface profile. The results can help understand the influence of plastic deformation on the rail corrugation initiation and growth. The creepage or stick-slip condition greatly influences the residual stresses and strains. While the residual strains and surface displacements increased at a reduced rate with increasing rolling passes, the residual stresses stabilize after a limited number of rolling passes. The residual stresses and strains near the wave trough of the residual wavy deformation are higher than those near the wave crest.

Experimental and numerical investigation of the effect of rail corrugation on the behaviour of rail fastenings

This paper presents the results of a detailed investigation of the effects of rail corrugation on the dynamic behaviour of metro rail fastenings, obtained from extensive experiments conducted on site and from simulations of train–track dynamics. The results of tests conducted with a metro train operating on corrugated tracks are presented and discussed first. A three-dimensional (3D) model of the metro train and a slab track was developed using multi-body dynamics modelling and the finite element method to simulate the effect of rail corrugation on the dynamic behaviour of rail fastenings. In the model, the metro train is modelled as a multi-rigid body system, and the slab track is modelled as a discrete elastic support system consisting of two Timoshenko beams for the rails, a 3D solid finite element (FE) model for the slabs, periodic discrete viscoelastic elements for the rail fastenings that connect the rails to the slabs, and uniformly viscoelastic elements for the subgrade beneath the slabs. The proposed train–track model was used to investigate the effects of rail corrugation on the dynamic behaviour of the metro track system and fastenings. An FE model for the rail fastenings was also developed and was used to calculate the stresses in the clips, some of which rupture under the excitation of rail corrugation. The results of the field experiments and dynamics simulations provide an insight into the root causes of the fracture of the clips, and several remedies are suggested for mitigating strong vibrations and failure of metro rail fastening systems.

Rail corrugation formation studied with a full-scale test facility and numerical analysis:

Abstract The current paper reviews and discusses the results of some important papers on rail corrugation in detail, and introduces the experimental study on mechanism of rail corrugation formation on curved track carried out using a full-scale test facility. The corrugation with different wavelengths on the test wheel tread is reproduced in the experiment. It is found that the passing frequency of the reproduced corrugation is the same as the excited natural frequency of the test rig. The natural frequencies of the test rig are identified through the modal experiment of the test rig using impulse method. The corrugation in the experiment is numerically analysed in the paper. In the analysis the contact geometry and steady creepage of the wheels/rollers in rolling contact are calculated. Kalkers rolling contact theory with non-Hertzian form is modified and used to calculate the frictional work density in the contact area of the wheel/roller. A model concerning the material loss per unit area proportional to the frictional work density is used to determine the wear on the contact surface of the wheel. The numerical results are in good agreement with the experimental results. They show that the test rig vibrating at high frequency can initiate a corrugation passing the same frequency on the smooth contact surface of the wheel under specific test conditions. The specific conditions include the non-zero steady creepage of the wheelset/rollers, the circumference of the wheel rolling circle approximately equal to multiple of the corrugation wavelength. The corrugation wavelength depends on the excited natural frequency of the test rig and the rolling speed of the wheelset. The depth and growth speed of corrugation depend on the fluctuation amplitude of the contact normal load of the wheelset/rollers.

An investigation into the mechanism of metro rail corrugation using experimental and theoretical methods

Severe short-pitch rail corrugation was found to have occurred on four types of track on the same metro line. Field investigations found that, even with the same operation conditions, the corrugations had different wavelengths for the different types of track. Impact hammer tap tests were conducted to investigate the dynamic behaviour of the tracks. The test results showed that, in the investigated metro, short-pitch corrugations are associated with the resonance behaviour of the tracks. The test results also showed that the corrugations on the investigated tracks are not caused by torsional vibration due to the wheelsets. Numerical simulations were conducted to identify the resonance behaviour that is could not be observed in the impact hammer tests due to the limitations in the test method. Three-dimensional finite element models for the four types of track were established and they were used to study the dynamic characteristics of the different tracks. The resonance frequencies and modes that are related to the generation of the corrugation were clearly identified in the numerical modelling studies; this further verifies the relationship between the formation of corrugation and the resonance behaviour of the tracks. The effect of a low value of the fastener stiffness on the dissipation of wheel/rail vibration energy was investigated with the help of numerical simulations. Both experimental and numerical results showed that the resonance behaviour of track structures is of great importance in determining the initiation, characteristics and development of the short-pitch corrugation on the investigated tracks.

Effects of Track Support Failures on Dynamic Response of High Speed Tracks

A model is proposed in this paper for investigating the effect of track support failures on the dynamic response of high speed tracks. In this model, the rails are modeled as two Timoshenko beams resting on discrete sleepers and interacting with a moving vehicle. The lateral, vertical and torsional deformations of the beams are all taken into account. Support failures are realized by changing the support stiffness and damping. To simulate the traveling of the vehicle along the track, the discrete supports to the rails are assumed to move backward at the train speed. Normal wheel/rail contact forces are calculated using the Hertzian contact theory and tangential (creep) wheel/rail forces are determined using Shen et al.s nonlinear creep theory. Differential equations of the vehicle/track system are solved by means of an explicit integration method. Effects of zero to six failed supports are simulated. Numerical results indicate that track support failures greatly affect the dynamic response of a tangent track. As the number of disabled supports increases, the normal wheel/rail forces, track displacement and track acceleration increase quickly, accelerating deterioration of the track.

Measurement and assessment of out-of-round electric locomotive wheels

This paper presents a detailed investigation of out-of-round electric locomotive wheels through extensive measurement conducted at field sites. More than 2000 wheels, of seven types of locomotives widely used in China, have been measured since April 2013. The measurement results indicate that two types of freight traffic locomotives suffer serious polygonal wear problems with center wavelengths ranging from 160 to 315 mm. The dominating wavelength is 200 mm. Therefore, the investigations are mainly focused on the two locomotive types. The other types, which are taken for comparison, do not exhibit obvious polygonal wear. However, they exhibited more or less eccentricity. The effect of wheel re-profiling on the wheel polygon is also investigated and discussed. The dominating harmonic orders and center wavelengths after re-profiling are consistent with those before re-profiling at the correct circumstances, if the center wavelength of the polygonal wear is about 200 mm.