UK researchers aim to tackle railway challenges
by James Morgan
16 August 2012
http://www.scienceomega.com Thu, 23 Aug 2012 09:31:00 BST
Researchers from the new Institute of Railway Research at the University of Huddersfield intend to address one of the most complex issues in engineering – the relationship between a locomotive’s wheel and the rail. The Institute’s 12-strong research team will work to deliver greater safety and cost efficiencies for the United Kingdom’s rail network.
Under the guidance of Professor Simon Iwnicki, deputy chair of the Railway Division at the Institution of Mechanical Engineers, the research team will investigate the nature of the contact between rolling stock and the track. A better understanding of this point of contact, which is only around the size of a thumbnail and typically lasts for a matter of milliseconds, could facilitate the optimisation of materials and designs used to manufacture tracks and wheels.
In an interview with ScienceOmega.com, Professor Iwnicki explained more about the complex relationship, and discussed how research within this field could help to mitigate rising rail fares. I began by asking Professor Iwnicki about the challenges involved in studying this interaction.
"There are lots of challenges," he replied. "The relationship between wheel and rail has been described as one of the most challenging in engineering. Obviously, it has been around for a long, long time. Broadly speaking, we still use steel wheels and rails that George Stephenson would have been familiar with. Even so, our understanding has developed enormously over the years. The main challenge is posed by the fact that all of a railway vehicle’s forces are carried through a very small contact patch between the wheel and the rail. A typical axle load for a vehicle is around 25 tonnes. That means that you have 12.5 tonnes on each thumbnail-sized contact patch. This is just the vertical load. A train also has to accelerate, brake, navigate curves in the line, and all of these pressures are communicated through the tiny contact patches. Moreover, with a vehicle moving at any sort of speed, this happens in milliseconds."
I asked Professor Iwnicki how scientists are able to study an interaction that is so small and fleeting.
"One of the most interesting studies was carried out by the German physicist Professor Heinrich Hertz in the 1880s. Hertz was quite an interesting character; he did much of his best work whilst working as a research assistant in Berlin in his 20s. He worked in lots of different areas such as fluids and hydraulics, but he conducted some particularly interesting investigations into contact. We still use some of his findings concerning how bodies react when they are pressed into contact with one another.
"However, Hertz’s work makes some big simplifications. For example, it assumes that materials are elastic. Actually, steel can behave plastically when bearing high loads. Initially, it behaves elastically, which means that if you remove a load it returns to its previous shape. However, it deforms plastically as the load increases, meaning that it doesn’t return to its previous shape. The problem with this kind of loading is that damage can be caused to the constituent material. Cracks can grow as the load is repeatedly added and removed. During their lifetimes, a point on the rail will undergo millions of wheel passages and a wheel will go through millions of cycles. As a result, fatigue cracks can grow and they can result in the rail failing.
"Computer models now play an important role in our work. We have developed commercial packages capable of predicting, in detail, exactly what is happening in the contact patch. We still don’t understand everything. There is much work to be done but every year we increase our knowledge of what is going on at this point of contact. We have also conducted some laboratory tests which will enable us to validate some of the latest computer models."
Huddersfield’s new hub for railway research is already thriving with activity, but how will a greater understanding of wheel-rail interaction benefit the United Kingdom’s railway network?
"We have been working alongside academic colleagues and industry partners to optimise the profile of the wheel and the rail," said Professor Iwnicki. "By improving its cross-sectional shape, we should be able to even-out or apply stresses to the most appropriate points. We are also interested in optimising maintenance techniques. Maintenance is very expensive, and so is replacement. There are big gains to be made by optimising the areas in which money is spent."
It was reported yesterday that rail fares in England are set to rise at a rate higher than inflation for the 10th successive year. I concluded our interview by asking Professor Iwnicki whether he was hopeful that his research would serve to slow the increasing costs of train tickets.
"That is a very difficult question for me to answer," he replied. "There are so many different factors that influence the levels at which operators set their prices. Even so, I think that reductions in operating costs will eventually feed through into reduced prices for passengers. We are also interested in the railway’s freight sector. It is a major European priority to move freight from the roads onto the rails. However, pricing can be a very sensitive issue when it comes to freight. In order to improve this situation, we are trying to work alongside the railway industry to develop better methods for charging freight and passenger operators accordingly. If an operator invests in vehicles that cause less damage to the track, it should pay lower access charges to run those vehicles.
"The United Kingdom and Sweden are the only countries that currently recognise track-friendly vehicles within their pricing schemes. The problem at the moment – even in the UK and in Sweden – is that the feedback mechanism is weak. It is possible to improve designs to benefit the rail infrastructure, but this involves increased costs for vehicle manufacturers. At present, the incentives are insufficient to encourage this to happen. The recent EU project CATRIN (Cost Allocation of TRransport INfrastructure cost) tried to introduce fairer charging mechanisms. It attempted to share the benefits of track-friendly vehicles across the whole railway system. If we implemented a similar system, there would be an incentive for operators to invest in track-friendly vehicles as they would incur lower track access charges."
