Roger Enblom

Deterioration mechanisms in the wheel–rail interface with focus on wear prediction: a literature review

Wheel–rail interface management is imperative to railway operation and its maintenance represents a major share of the total maintenance cost. In general, the course of events usually called wear is a complicated process involving several modes of material deterioration and contact surface alteration. Thus material removal or relocation, plastic flow and phase transformation may take place at, just below, or in-between the contacting surfaces. A higher degree of predictability of deterioration mechanisms and a firm basis for optimisation of the wheel–rail system are anticipated to reveal a great potential for cost savings. Wear in the sense of material loss and related wheel–rail profile evolution represents one of several modes of damage. The purpose of this survey is to explore research on wear simulation, to some degree extended to neighbouring disciplines. It is believed that a cross-disciplinary approach involving, for instance, adhesive and abrasive wear, surface plasticity, and rolling contact fatigue opens new perspectives to improved damage prediction procedures.

Proposed Procedure and Trial Simulation of Rail Profile Evolution Due to Uniform Wear

Abstract A procedure for numerical simulation of rail wear and the corresponding profile evolution has been formulated. The wear is assumed to be uniform in the sense that the profiles remain constant along the track portion to be investigated. A simulation set is selected defining the vehicles running on the track, their operating conditions, and contact parameters. Several variations of input data may be included together with the corresponding occurrence probability. Simulation of multi-body dynamics is used to calculate contact forces and positions, and Archards wear equation is applied for the calculation of wear depth. Wear coefficients as a function of contact pressure and relative sliding velocity are collected from different test results. Trial calculations of four non-lubricated and two lubricated curves with radii from 303 to 802m show qualitatively reasonable results in terms of profile shape development and difference in wear mechanisms between gauge corner and rail head. The wear rates related to traffic tonnage are, however, overestimated and the lubrication efficiency underestimated. It is expected that model refinements in terms of environmental influence and contact stress calculation are useful to improve the quantitative results.

An Alternative to FASTSIM for Tangential Solution of the Wheel-Rail Contact

ABSTRACT In most rail vehicle dynamics simulation packages, tangential solution of the wheel–rail contact is gained by means of Kalkers FASTSIM algorithm. While 5–25% error is expected for creep force estimation, the errors of shear stress distribution, needed for wheel–rail damage analysis, may rise above 30% due to the parabolic traction bound. Therefore, a novel algorithm named FaStrip is proposed as an alternative to FASTSIM. It is based on the strip theory which extends the two-dimensional rolling contact solution to three-dimensional contacts. To form FaStrip, the original strip theory is amended to obtain accurate estimations for any contact ellipse size and it is combined by a numerical algorithm to handle spin. The comparison between the two algorithms shows that using FaStrip improves the accuracy of the estimated shear stress distribution and the creep force estimation in all studied cases. In combined lateral creepage and spin cases, for instance, the error in force estimation reduces from 18% to less than 2%. The estimation of the slip velocities in the slip zone, needed for wear analysis, is also studied. Since FaStrip is as fast as FASTSIM, it can be an alternative for tangential solution of the wheel–rail contact in simulation packages.

Wheel-rail contact mechanics

Abstract: The scope of this chapter is the modelling of the force balance at the wheel–rail interface in railway vehicles. The focus is on simulation of vehicle dynamics and the requirements imposed on numerical efficiency. The introductory section addresses basic concepts related to profile geometry and contact area and is followed by a section on general models for normally and tangentially loaded contacts. Analytical and numerical methods are treated. The section on wheel–rail-specific solutions concentrates on numerical algorithms for dynamic application. Comparisons between elliptic and non-elliptic models are given. The chapter concludes with a section on vehicle dynamics ranging from simulation of contact conditions to a review of available simulation packages.

Two-level numerical optimization of ride comfort in railway vehicles

Abstract This article addresses the interaction between and tuning of different mechanical subsystems in railway vehicle design. Application of numerical methods in a two-level optimization process, involving multi-body vehicle dynamics simulation and finite-element structural analysis, is proposed. The focus is on vibration ride comfort and tuning of dynamic properties of the vehicle, running gear, and carbody structure. As a background, a brief overview of multi-disciplinary and structural optimization methods is given. The selected solution based on the loosely coupled collaborative optimization approach, here implemented as a two-level structure, is presented. Numerical examples are provided to illustrate the choice of optimization algorithms suitable for this type of resonant systems and to demonstrate the performance of the numerical procedures on a realistic engineering problem. The leading coach of a three-car train-set is successfully optimized in terms of mass reduction and reduced natural frequency requirements, despite an infeasible initial design.

Influence of wheel-rail contact modelling on vehicle dynamic simulation

This paper presents a comparison of four models of rolling contact used for online contact force evaluation in rail vehicle dynamics. Until now only a few wheel–rail contact models have been used for online simulation in multibody software (MBS). Many more models exist and their behaviour has been studied offline, but a comparative study of the mutual influence between the calculation of the creep forces and the simulated vehicle dynamics seems to be missing. Such a comparison would help researchers with the assessment of accuracy and calculation time. The contact methods investigated in this paper are FASTSIM, Linder, Kik–Piotrowski and Stripes. They are compared through a coupling between an MBS for the vehicle simulation and Matlab for the contact models. This way the influence of the creep force calculation on the vehicle simulation is investigated. More specifically this study focuses on the influence of the contact model on the simulation of the hunting motion and on the curving behaviour.

Investigation of the risk for Rolling Contact Fatigue on wheels of different passenger trains

Of late, rolling contact fatigue (RCF) has become more common on wheels of passenger trains. Cracks initiated at the wheel surface have been found on certain trains, which has led to wheel damage and more frequent re-profiling, reducing the lifetime of the wheels. Two possible theories to predict circumferential RCF have been identified, i.e. the shakedown theory and damage function. Investigations have been performed with the MBS simulation tool SIMPACK. The wheel profiles in the investigations are mainly P8 and S1002. In principle, the correlation between field observations and predicted damage is fairly good. It is concluded that both the shakedown theory and damage function can be used for indicative predictions using quasi-static simulations. With the limitations of the study, some guidelines are given for the assessment of results from quasi-static simulations in curves.

Design of HVDC converter station equipment subject to severe seismic performance requirements

Severe seismic design levels were specified for the upgrading of the HVDC link between the principal islands of New Zealand. A number of novel design solutions were required to fulfil the performance requirements for the electric equipment. The purpose of this paper is to give an overview of design solutions and verification methods in the light of a specification stating performance criteria rather than specific allowables. Modifications to items of high voltage electrical equipment are described that reduce the seismic loads in the equipment and enable standard equipment to be used in areas of high seismicity. The seismic performance is further improved by controlling the eventual collapse mechanism. >

On integrated wheel and track damage prediction using vehicle-track dynamic simulations

The renewal costs for wheels and rails are a substantial part of the costs for rolling stock operators and infrastructure managers all over the world. The causes for reprofiling or grinding are, in most cases, related to the following: (1) wheel or rail profiles with unacceptable wear, (2) appearance of rolling contact fatigue cracks in the surface, and (3) wheel flats caused by locking wheels during braking. The first two causes are related to the dynamic behavior of the vehicle–track system, and can be predicted using multibody simulations. However, there are several limitations that restrain the usefulness of these prediction techniques, such as simulation time constraints, necessary simplifications, and lack of experimental data that lead to educated assumptions. In this paper, we take the end-user perspective in order to show whether the latest developments in wheel–rail damage prediction can be integrated in a simplified framework, and subsequently used by the different stakeholders for an improved management of the different assets involved in the operation of rail vehicles.