Derailment at Eschede is the 5th episode of Seconds from Disaster, researching how did this high-speed train crash.
A wheel of the InterCity Express (ICE) No. 884 'Wilhelm Konrad Röntgen' fails during travel in Eschede, Germany. The train derails and collides with a bridge, killing 101 people and injuring 88.
The ICE 1 trains were equipped with single-cast wheels, known as monobloc wheels. Once in service it soon became apparent that this design could, as a result of metal fatigue and out-of-round conditions, resulting in resonance and vibration at cruising speed. Passengers noticed this particularly in the restaurant car, where there were reports of loud vibrations in the dinerware and of glasses "creeping" across tables.
Managers in the railway organization had experienced these severe vibrations on a trip and tried to have the problem solved. In response engineers decd that to solve the problem: the suspension of ICE cars could be improved with the use of a rubber damping ring between the tire and the wheel body. A similar design had been employed successfully in trams (known as resilient wheels), though at significantly lower speeds. This new wheel, dubbed a "wheel-tire" design, consisted of a wheel body surrounded by a 20 mm thick rubber damper and then a relatively thin metal tire. The new design was not tested at high speed before it was made operational, but was successful at resolving the issue of vibration at cruising speeds.
At the time, no facilities existed in Germany that could test the actual failure limit of the wheels, and so complete prototype were never tested physically. The design and specification relied greatly on available material data and theory. The very few laboratory and rail tests that were performed did not measure wheel behavior with extended wear conditions or greater than cruising speeds. Nevertheless, during a period of years the wheels proved themselves apparently reliable and, until the accident, had not caused any major problems.
The Fraunhofer Institute was charged with the task of determining the cause of the accident. It was revealed later that the institute had told the DB management as early as 1992 about its concerns about possible tire failure. During the months prior to the accident, Ustra, the company that operates Hanover's tram network reported that the tires employed in its trains were failing much earlier than expected based on the failure limit estimates; it decided to replace the wheels much earlier than was required legally by the specification. In doing so, it reported its findings in a warning to all other users of wheels built with similar designs, including Deutsche Bahn.
It was soon apparent that dynamic repetitive forces had not been accounted for in the statistical failure modeling done during the design phase, and the resulting design lacked an adequate margin of safety. The following factors, overlooked during design, were noted:
- The tires were flattened into an ellipse as the wheel turned through each revolution (approximately 500,000 times during a typical day in service on an ICE train), with corresponding fatigue effects.
- In contrast to the monoblock wheel design, cracks could also form on the inside of the tire.
- As the tire became thinner due to wear, the dynamic forces were exaggerated, resulting in crack growth.
- Flat spots and ridges or swells in the tire increased the dynamic forces on the assembly dramatically and greatly accelerated wear.
During July 1997, Üstra discovered fatigue cracks in dual block wheels on trams running at about 24 km/h (15 mph). It began changing wheels before fatigue cracks could develop; Üstra then messaged other railway companies. According to the tram company, during autumn 1997, when Üstra notified Deutsche Bahn, they replied by stating that they had not noticed problems in their trains.