Analysis Of Wheel-rail Contact Research Articles

Analysis of wheel-rail contact under oil lubrication conditions

Abstract This investigation centers on the characteristics of the contact between the wheel and rail when lubricated with oil, with a consideration of the impact of surface roughness. Confronting significant challenges related to low adhesion, a thorough examination is undertaken to analyze the changes in film thickness under oil lubrication, investigating trends at varying vehicle speeds and axle loads. Employing detailed modeling based on micro-elastohydrodynamic theory, the distribution of oil film thickness under diverse operational conditions is determined. The findings indicate that, under oil lubrication, a film thickness in the range of several tens of micrometers is established, effectively insulating the surfaces of the wheel and rail, thereby reducing adhesion. With increasing vehicle speed, the thickness of the oil film also rises, whereas an elevation in axle load results in a marginal decrease in film thickness. This research contributes to a comprehensive comprehension of the wheel-rail contact mechanism in oil lubrication scenarios, providing theoretical backing to address concerns related to low adhesion. The implications are substantial for improving the safety and economic efficiency of efficient railway transportation.

Comparison between quasi-static and multibody dynamic simulations for wheel-rail contact analysis

Comparison between quasi-static and multibody dynamic simulations for wheel-rail contact analysis

Nonlocal thermomechanical coupled analysis of wheel-rail contact using a peridynamic model

Nonlocal peridynamic (PD) theory is widely used in damage and thermomechanical coupling simulations. This study applied ordinary state-based PD thermomechanics to model the wheel-rail contact bringing temperature-dependent materials. A two-dimensional coupled thermomechanical model was developed to predict the evolution of the thermomechanical response, thermal damage, and wear in railway rail. The model was verified based on the displacement and temperature fields of the rail. The model results correlated well with the finite element model and analytical method results. The influence of the vehicle speed, rail surface cracks, and wheel idling on the thermomechanical response of the rail was also evaluated in detail. The results show that the influence of the vehicle speed on the temperature field is much greater than that of the contact stress. The contact temperature under the critical creepage could lead to the formation of a brittle white etching layer (WEL). Cracks on the rail surface increased the contact stress and temperature peaks. Thermomechanical loading also promoted rail surface damage. Continuous thermomechanical loading due to wheel idling softened and removed rail surface materials, forming wear pits and a WEL, known as wheel burns.

Fragility analysis for vehicle derailment on railway bridges under earthquakes

With the rapid development of high-speed railways around the globe, the safety of vehicles running on bridges during earthquakes has been paid more attention to. In the design of railway bridges, in addition to ensuring the safety of the bridge structure in earthquake, the vehicle safety should also be ensured. Previous studies have focused on the detailed analysis of vehicle derailment on bridges, proposing complex numerical algorithms for wheel–rail contact analysis as well as for parametric analysis, but they are inconvenient for designers. Intensity measure (IM) used in performance-based earthquake engineering is introduced in this study. A method to evaluate the vehicle safety on bridges under earthquakes is proposed with respect to the optimal IM. Then, the vehicle derailment case of the Kumamoto earthquake in Japan verifies the decoupling method of vehicle–bridge interaction model. In the assessment of vehicle derailments, eight IMs are systematically compared: the IMs of bridge deck motion are generally better than those of ground motion; the variation coefficient of spectral intensity of the bridge deck is the smallest at different frequencies. Finally, the derailment fragility cloud map is presented to evaluate the vehicle safety on bridges during earthquakes.

Fatigue life analysis of wheel-rail contacts at railway turnouts using finite element modelling approach.

The article deals with wheel-rail contact analysis at railway turnout using a finite element modelling approach. The focus is understanding the wheel-rail contact problems and finding the means of reducing these problems at railway turnouts. The main aim of the work reported in this article is to analyse fatigue life and simulate the wheel-rail contact problems for a repeated wheel loading cycle by considering the effect of normal and tangential contact force impact under different vehicle loading conditions. The study investigates the impact of tangential contact force generated due to different-angled shapes of the turnout and aims to reveal how it affects the life of contacting surfaces. The obtained results show that the maximum von-Mises equivalent alternating stress, maximal fatigue sensitivity, and maximum hysteresis loop stresses were observed under tangential contact force. These maximum stresses and hysteresis loops are responsible for rolling contact fatigue damage, and excessive deformation of the wheel-rail contact surface. At a constant rotational velocity, the tangential contact force has a significant impact on the fatigue life cycle and wheel-rail material subjected to fatigue damage at lower cycles compared to the normal contact force. The finite element modelling analysis result indicated that the contact damages and structural integrity of the wheel-rail contact surface are highly dependent on contact force type and can be affected by the track geometry parameters.

An effective method for calculating elasto-plastic contact pressure and contact patch size under elliptical, circular and line contact conditions

According to the Hertz's contact theory (HCT) and considering the strain hardening of materials, an effective calculation method is proposed for solving the elasto-plastic contact pressure and the contact patch size under arbitrary smooth and continuous contact conditions. Firstly, it is assumed that the outer and inner edges of the contact patch are elastic and elasto-plastic contact zones, respectively, the contact pressure in the elastic contact zone satisfies the HCT, while the contact pressure in the elasto-plastic contact zone is the superposition of a constant contact pressure and several small ellipsoidal distribution contact pressures. Then, the explicit expressions of contact patch size and contact pressure under the elasto-plastic elliptical, circular and line contact conditions are derived, respectively. Subsequently, the accuracy and applicability of the proposed method are evaluated by comparing the predicted results with the finite element simulations. Finally, the accuracy of the proposed method is further verified by comparing the predicted results with the typical results in literature. It is shown that the proposed method has high calculation accuracy, and the maximum relative errors are 9.32% for the elliptical contact, 4.61% for the circular contact and 11.84% for the line contact, respectively. Meanwhile, the proposed method can effectively predict the contact pressure distribution under the elasto-plastic elliptical, circular and line contacts, and shows a general applicability for different contact materials, contact-body's sizes and normal external loads, as well as for the elasto-plastic wheel-rail contact analysis.

An Innovative and Efficient Method for Reverse Design of Wheel-Rail Profiles

Well-designed wheel-rail profiles are not only helpful in achieving expected dynamic vehicle performance but also in extending the service lives of wheels and rails. In this paper, a method for designing wheel-rail profiles is presented based on the rolling radius difference. This method consists of three parts, i.e., the reverse designs of wheel profiles, symmetric rail profiles and non-symmetric rail profiles. A reverse design method for wheel-rail profiles that can obtain smooth profile formed by quadratic curves is established according to the mapping relation between the rolling radius difference and the wheel-rail profile gradient. This reverse design method is verified and an example for optimizing the design of wheel profiles is introduced. Results show that the design method is effective and efficient. The static/dynamic indexes of the optimized wheel profiles matched with CHN60 can be greatly improved. According to the comparative analysis of wheel-rail contact and dynamic performance, when the lateral displacement reaches 6 mm, the maximum contact stress will be distributed evenly and can be decreased by 184.4 MPa compared to that of existing profiles, while the critical speed can be increased by 10.8% and the running stability can be improved by around 7%. It can be seen that this method is useful for the design of new wheel-rail profiles and optimization of existing wheel-rail profiles.

Evaluation of wheel profile measurements by means of the contact-point function for the wheel–rail interface

This study examines the accuracy of a wayside train wheel profile measurement system. This was accomplished by an evaluation of the contact-point function for the wheel–rail interface. The wheel profile measurement system in question generates data about the wheel profiles of passing trains. These data are used for improving the wheel maintenance procedures for the rolling stock operator. Recent work shows that there are differences between the data from the two different units in the system, but how this influences further use of the data, e.g. in wheel–rail contact analysis, has not been investigated so far. Accordingly, this article shows how two key wheel measures (the wheel flange thickness and the wheel profile) impact on the contact-point function and which of these measures has the largest impact on the contact-point function. The data used in this study were generated by two different measurement units for the same wheel and with the same wheel status. The results show that the different units produce different results and that these differences are more prominent when a difference in the flange thickness is detected, with a resulting shift of the front side of the flange and of the tread. With no difference in the flange thickness, i.e. no shift of the front side of the flange and of the tread, a difference was still detected in the contact conditions. Furthermore, this investigation shows that the shape of the tread has a greater impact on the contact-point conditions compared to a change in the flange thickness of up to 2.5 mm. This difference in the tread shape could have originated in measurement noise or different wheel measurement positions. The results of the study also show the importance of managing the measurement quality before using the data, for example for maintenance decisions.

Analysis of Wheel-Rail Contact under partial slip and low speed conditions

The paper analyzes applicability of rolling contact simulation in low speed and adhesion conditions. Additionally, transition zone of the coefficient of friction is implemented. Efffects of the friction coefficient are examined to the forces which are normal and tangential components. Various comparative studies are also computed and differences between numerical results with results of the comparative studies are observed for validation. The results show that outputs of developed FEM model are compatible with comparative studies. Transition zone of the coefficient of friction directly affects the traction force at low speed conditions.DOI: http://dx.doi.org/10.5755/j01.mech.23.1.13779

차륜-레일 2점 접촉을 고려한 3차원 윤축 동역학 해석

윤축 동역학 해석은 철도차량 동역학 해석의 정밀도를 결정하는 핵심 요소이다. 본 연구에서는 정밀한 3차원 차륜-레일 접촉 해석을 윤축의 강체 운동 방정식에 적용하는 방법으로 3차원 윤축 동역학 해석을 수행하였다. 곡선 주행시 플랜지 접촉에 의해 차륜-레일 2점 접촉이 발생할 때 윤축의 동역학 해석이 가능한 수치해석 절차를 개발하였다. 윤축의 구속조건식과 강체 동역학 방정식을 Runge-Kutta 방법을 이용하여 수치적분을 수행하였다. 제안된 윤축 동역학 해석 결과는 VI-RAIL을 이용한 해석결과와 비교 분석하여 타당성을 검증하였다. Wheelset dynamic analysis is a key element to determine the degree of accuracy of railway vehicle dynamics. In this study, a three-dimensional wheelset dynamic analysis is presented in such a way that the precise wheel-rail contact analysis in three-dimension is implemented into the dynamic equations of a wheelset. A numerical procedure that can be used for the analysis of a wheelset dynamics when the wheel-rail two point contact occurs in a cornering maneuver is developed. Numerical solutions of the constraint equations and the dynamics equations of a wheelset are achieved by using Runge-Kutta method. The proposed wheelset dynamic analysis is validated by comparison against results obtained from VI-RAIL analysis.

Development and implementation of a differential elastic wheel–rail contact model for multibody applications

The wheel–rail contact analysis plays a fundamental role in the multibody modelling of railway vehicles. A good contact model must provide an accurate description of the global and local contact phenomena (contact forces, position and shape of the contact patch, stresses and displacements) and a general handling of the multiple contact. The model has also to assure high numerical efficiency (in order to be implemented directly online within multibody models) and a good compatibility with commercial multibody software (Simpack Rail, Adams Rail). In this work, an elastic wheel–rail contact model that satisfies the previous specifics is presented. The model considers the wheel and the rail as elastic deformable bodies and requires the numerical solution of Navier's elasticity equation. The contact between wheel and rail has been described by means of suitable analytical contact conditions. Subsequently, the contact model has been inserted within the multibody model of a benchmark railway vehicle (the Manchester Wagon) in order to obtain a complete model of the wagon. The model has been implemented in the Matlab/Simulink environment. Finally, numerical simulations of the vehicle dynamics have been carried out on many different railway tracks with the aim of evaluating the performances of the model. The results obtained with the proposed method have been compared with those obtained by means of a standard commercial software. The main purpose is to achieve a better integration between the differential modelling and the multibody modelling. This kind of integration is almost absent in the literature (especially in the railway field) due to the computational cost and to the memory storage needs. However, it is very important because only the differential modelling allows an accurate analysis of the contact problem (in terms of contact forces, position and shape of the contact patch, stresses and displacements) while the multibody modelling is currently the standard in the study of the railway dynamics.

A lookup table-based method for wheel–rail contact analysis

This article describes an investigation on the relative motion between wheel-set and rails. Through the search of an equilibrium configuration, the positions of contact points between rails and wheels are first located. The detection methods allow also the definition of the normal unit vectors to rail and wheel at contact points. To reduce computing time, the results are stored in a lookup table accessed during the dynamic analyses of wheel-sets, bogies, or trains. The use of lookup table considerably speeds up contact detection when numerically integrating with respect to time.

Modelling of wheels and rail discontinuities in dynamic wheel–rail contact analysis

A classification of wheel–rail contact is given. Difference is made between modelling of a running wheel with continuous single-point-contact, as is common practice in wheel–rail contact analysis, and a wheel with transient double- or multi-point-contact, which may occur for rail irregularities with curvatures larger than that of the wheel circumference. It is shown that application of the first model for these irregularities will strongly underestimate the contact forces as it does not describe occurring mechanisms correctly. Further, it is shown that in principle it is not possible to describe the second type of contact fully correct with a lumped wheel model. Both wheel models are formulated mathematically for some basic contact cases. Afterwards, results are applied to a linear track model. Analytical closed-form solutions are found in the frequency domain for arbitrary type of contact and numerically transformed to the time domain. Finally, the necessity is shown to avoid situations where transient multiple-point-contact may occur (like rail joints) in practice.