New methodology for rail grade selection

Which steel quality should you choose for your rail? Until now, this was usually determined based on track layout and geometry for the given location (e.g. curve radius). However, there is a growing desire to take into account the occurring loading conditions in the wheel-rail contact. This more specific approach would decrease the chance of ‘unpleasant surprises’ during the lifecycle of the rail. At the request of the Dutch infrastructure manager ProRail, DEKRA Rail and Delft University of Technology are currently investigating to develop a new methodology which will predict the expected damage development of a rail over time depending on the occurring load. The eventual goal? To gain more insight in wear and fatigue behavior of the various rail grades in order to justify the choice of rail material per location and to plan maintenance more effectively and at lower costs.

Railway line

Research into rail defects
Bart Schotsman, system specialist at ProRail, is a familiar face at DEKRA Rail, as he collaborated with many DEKRA Rail experts during his career at ProRail. One of these experts is mechanics specialist Martin Hiensch. Martin already investigated rail defects for ProRail in the 90s and is currently working on his PhD thesis at Delft University. Bart: “In the 90s we mainly focused on hard materials and different rail profiles. We also started grinding the rail more frequently. Unfortunately, these hard materials are expensive in purchase and maintenance, so logically we wanted to start working with cheaper, softer materials. But in order to do so, we need to first figure out what the wear and fatigue behavior of the materials is in different applications. In the context of his PhD research, I got in touch with Martin about this matter.

“An important benefit of the two-disc method is that we can manage and control the settings of the wheel-rail load conditions.”

Imitating wheel-rail contact
To answer the main question that ProRail has, it was Martin’s proposal to use the two-disc research method. This method means that the wheel-rail contact is simulated on scale in a lab using one disc of wheel material and one disc of rail material. The set-up in the two-disc machine is carefully chosen in order to ballance the chosen axial force, slip and geometry, aiming at realistic contact conditions. Martin: “An important benefit of the two-disc method is that we can manage and control the settings of the wheel-rail load conditions. When we would test ‘in the field’, we experience a lot of variation caused by for instance different vehicles, axle load, speed, or even influences of the weather. For the set-up of damage models and the prediction of the behavior of the rail under specific circumstances, it is important to keep the spread of load conditions as small as possible.”

Testing two-disc machines
The use of the two-disc machine is not unique, but the application is. Bart: “Often, the two-disc machine is used for testing materials under extremely heavy loads. When you significantly increase the load, the direct impact is visible much quicker. However, this method only tests wear and in Martin’s two-disc research, the model to be validated is focused on wear and fatigue damage (cracks). This makes the approach unique.”

A more targeted purchasing and maintenance plan for rails
The project is currently in the validation phase. Bart hopes that, with Martin’s research, he can take the first step to a more targeted purchase and maintenance plan for ProRail’s rail. Martin: “When the result of this validation is positive, we will move on to the next phase in the project; deriving damage functions for rail qualities for which these currently are not available. Eventually, the intended damage functions will allow infrastructure managers to choose rail material based on the given loading conditions and maintenance process, which leads to an optimal performance. Optimal in terms of costs, but also especially in terms of reliability and availability of the rail system.”

March 2018

Share page