When a freight train derailed on the Iron Ore Line (Malmbanan) on December 17, 2023, it caused extensive damage and major traffic disruptions. The accident investigation is now complete, and the analysis - in which researchers at Chalmers played a key role - reveals a previously unknown damage mechanism in train wheels.
“This gives us new knowledge that could influence both design and maintenance,” says Anders Ekberg, Professor of Railway Mechanics at Chalmers University of Technology.
The investigation report, published on May 22, follows an extensive technical analysis. At the center is a wheel that cracked all the way to the hub and lost its grip on the axle, causing it to shift inward. The damaged wheel then rolled for 15 kilometers on the inside of the rail before the train derailed. The resulting damage was severe.
“What happened is an example of what we call a fatigue fracture,” says Anders Ekberg. “You can compare it to bending a teaspoon back and forth until it breaks. It’s not a sudden overload that causes the break, but many repeated small loads.”
Crack in an unexpected location
The crack that caused the fracture originated on the inside of the so-called wheel flange — an unusual and previously unexpected location for this type of damage. The analysis showed that two types of loads likely interacted: flange contact during curve negotiation and heating of the flange due to contact with a brake block. The heat caused compressive stresses that, upon cooling, turned into tensile stresses, which in turn accelerated the growth of the crack.
“Being able to identify multiple contributing factors behind the crack formation was key to understanding the course of events,” says Anders Ekberg. “None of the loads were likely sufficient on their own, but together they could drive a slowly growing fracture that ultimately led to failure.”
Development of future standards
To support the conclusions, the investigation used numerical simulations, material testing, and expert analysis. The research work builds on long-standing expertise within the framework of CHARMEC (Chalmers Railway Mechanics) and has also led to the development of new analytical models. The results have already been summarized in two scientific articles.
“This is a clear example of how research can contribute both to accident investigations and the development of future standards,” concludes Anders Ekberg. “There is now a technical basis for updating both design rules and maintenance strategies to help prevent similar accidents in the future.”
- Full Professor, Dynamics, Mechanics and Maritime Sciences