The crucial interface: the wheel-rail interface is fundamental to rail transport: any failure in this area can have fatal consequences. Pavel Manasek of the Bonatrans Group and a member of the 15th International Wheelset Congress organising committee, previews what speakers will be saying on this vital subject
Pavel Manasek
RAILWAY wheels and wheelsets are rightfully considered safety-critical components for rolling stock as they are the point of contact between rail vehicles and the infrastructure–they must carry the train and guide it safely on the rails and through switches and crossings. Passenger trains are now running at higher speeds than ever before while freight trains are much heavier, which means wheelsets are having to withstand much higher static and dynamic forces. Their task is also to ensure safe and efficient braking through adhesion between wheel and rail. As wheel-rail contact is among the main sources of noise generated by rail vehicles, finding ways to reduce noise is a task of growing importance.
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The wheel-rail interface is a very complex issue where many factors come into consideration. Wheels are loaded by a multiaxial array of forces (Figure 1) influenced by vehicle dynamics, track geometry, and state of maintenance. Moreover, during braking, wheels often dissipate energy from the train which heats them to such high temperatures that the material properties of the wheels can be altered.
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Several of the papers being presented in Prague will focus on the damage caused to the wheel tread surface during operation. There are two main kinds of tread damage: rolling contact fatigue (RCF) and flats, both of which can lead to premature wheel reprofiling or removal, and eventually even to a wheel failure.
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In a paper from Japan on the evaluation of RCF properties in the martensite white layer in wheel steel, Japanese universities and wheelset manufacturers have been studying this type of damage, or more specifically spalling of the wheel tread (Figure 2), and have observed this phenomenon many times. A mathematical model using FEM analysis based on experimental data has been developed that can describe the initiation and propagation of cracks in the white layer on the wheel tread surface, which appears particularly in wheels with a high carbon content. The model enables evaluation of various loading conditions and their effect on RCF. Experiments and FEM analyses have confirmed wheel slippage as the main source of crack initiation in the white layer.
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High impact wheels
A group of authors from a Japanese wheel manufacturer have conducted an investigation of high impact wheels in their search for the main causes of a problem that causes large numbers of freight wagon wheels to be removed from service in North America. They believe the appearance of a martensite structure, spheroidised cementite, and a white layer are the main results of high impact wheels. To combat this, they propose an alternative wheel material with less inclination to high impact wheels.
The problem of wheel flats will be addressed by Mr M Steenbergen from Delft University, the Netherlands, who tries to bridge the considerable differences in results and standards for evaluating wheel flats, which are derived from either geometry or force-based criteria. Besides detailed analysis of wheel flats, Steenbergen offers a universal criterion of the minimum circumferential wheel tread curvature as the critical parameter.
As the wheel-rail interface in normal operating conditions is very complex, it is vital to get as much knowledge from experience out in the field as possible. However, it is a time consuming and costly task that requires the cooperation of many partners. The Wheelset Integrated Design and Effective Maintenance project (Widem) covers this task in a load measurement trial on the wheelsets of Czech Railways’ Pendolino train. A paper on the project will present the experience gained from wheel-rail load analysis conducted on an instrumented wheelset first on a full scale wheelset test bench, followed by real operation on a test track initially and then a mainline railway.
As field tests of wheelsets are costly, an alternative is mathematical modelling of the dynamic load of wheelsets on real track sections. Experts from the Silesian University of Technology in Poland have calculated monoblock wheel loads based on a simulation of dynamic impact of a coach model on a real track section in Poland. Two different programs were used to simulate this, which produced comparable results that were verified by experiments.
Experts from Siemens will explain how they exploited a simulation method, normally used to simulate vehicle dynamics, to determine the effect of track on wheelsets and their wear. The advantage of this is that the model and loading characteristics already exist and are used regularly by a vehicle manufacturer.
Hot topic
It is clear from many of the experts coming from universities as well as from manufacturers and operators, that the whole topic of wheel-rail contact problems is still the subject of much discussion. Complete understanding of this complex subject requires further diligent work and verification of theories and approaches. It is also clear that the wheel material is only part of the problem, as there are other important factors such as bogie and vehicle design and maintenance, as well as the state of the track.
Other issues covered under the theme of wheel-rail interaction will be: analysis of the wheel-brake shoe-rail system in operating conditions, dynamic loads of resilient tram wheels, loading of wheelsets for tilting trains, and mathematical models of various cracks and their influence on wheel fatigue life.
I hope this gives IRJ readers a taste of what to expect at the International Wheelset Congress where 70 papers will be presented. It looks set to be an interesting three days.
Congress highlights
EVERY three years, wheelset designers, manufacturers, researchers and other railway professionals from around the world gather at the International Wheelset Congress (IWC). This may not be the only event dedicated to railway wheels, but the fact that it is international provides a unique opportunity for wheel experts from all continents and all types of rail transport to their share experience.
The Czech wheelset manufacturer Bonatrans Group will host the 15th IWC in Prague from September 23 to 27 in association with the European Railway Wheels Association, the Union of European Railway Industries (Unife), and IRJ which is the official journal for the event.
The main themes to be covered are wheel-rail interaction, the fatigue life of wheelsets and their component parts, production technology and surface treatments, modern nondestructive testing technologies related to wheelsets, reducing noise, and life-cycle costs and maintenance.
A complete list of IWC papers can be found at the IWC website where you can also register to attend the congress: www.15wheelsetcongress.com
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