Editing Eschede train disaster (section)

===Wheel design===
The [[ICE 1]] trains were originally equipped with single-cast [[Wheelset (rail transport)|wheelsets]], known as [[Train wheel#Railway wheel and tire|monobloc wheels]]. Once in service it soon became apparent that this design could, as a result of [[metal fatigue]]{{Citation needed|reason=''wear'' would make more sense here|date=April 2017}} and uneven wear, result in [[resonance]] and vibration at cruising speed. Passengers noticed this particularly in the restaurant car, where there were reports of loud vibrations in the dinnerware and of glasses "creeping" across tables.

Managers in the railway organisation had experienced these severe vibrations on a previous trip and asked to have the problem solved. In response engineers decided that to solve the problem, the suspension of ICE cars could be improved with the use of a rubber damping ring between the rail-contacting [[Railway tire|steel tyre]] and the steel wheel body. A similar design (known as resilient wheels) had been employed successfully in [[tram]]s around the world, at much lower speeds. This kind of wheel, dubbed a ''wheel–tyre'' design, consisted of a wheel body surrounded by a {{Convert|20|mm|in|adj=mid|-thick}} rubber damper and then a relatively thin metal tyre. The new design was not tested at high speed in Germany before it was made operational, but was successful at resolving the issue of vibration at cruising speeds. Decade-long experience at high speed gathered by train manufacturers and railway companies in Italy, France and Japan was not considered.{{Citation needed|date=April 2023|reason=was this wheel structure tested or used anywhere at high speeds?}}

At the time, there were no facilities in Germany that could test the actual failure limit of the wheels, and so complete prototypes were never tested physically. The design and specification relied greatly on available materials data and theory. The very few laboratory and rail tests that were performed did not measure wheel behaviour with extended wear conditions or speeds greater than normal cruising.{{Clarify|date=April 2023}} Nevertheless, over several years the wheels had been reliable and, until the accident, had not caused any major problems.

In July 1997, nearly one year before the disaster, [[Üstra]], the company that operates Hanover's tram network, discovered fatigue cracks in dual block wheels on trams running at about {{convert|24|km/h|mph|abbr=on}}. It began changing wheels before fatigue cracks could develop, much earlier than was legally required by the specification. Üstra reported its findings in a warning to all other users of wheels built with similar designs, including [[Deutsche Bahn]], in late 1997. According to Üstra, Deutsche Bahn replied by stating that they had not noticed problems in their trains.<ref name="Seconds" />{{Rp|39:38}}

The {{Interlanguage link|Fraunhofer Institute for Structural Durability and System Reliability|de|3=Fraunhofer-Institut für Betriebsfestigkeit und Systemzuverlässigkeit}} ([[Fraunhofer Institute|Fraunhofer]] LBF) in Darmstadt 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 wheel–tyre failure.

It was soon apparent that dynamic repetitive forces had not been considered in the modelling done during the design phase,<ref>{{cite web |last=Griffith |first=Angela |title=Eschede Train Derailment |website=Root-Cause-Analysis.info |date=4 June 2009 |url=https://root-cause-analysis.info/2009/06/04/eschede-train-derailment/ |archive-url=https://web.archive.org/web/20230426104900/https://root-cause-analysis.info/2009/06/04/eschede-train-derailment/ |archive-date=2023-04-26 }}</ref> and the resulting design lacked an adequate margin of safety. The following factors, overlooked during design, were noted:
# The tyres 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 monobloc wheel design, cracks could form on the inside as well as the outside of the tyre.
# As the tyre wore thinner, dynamic forces increased, causing crack growth.
# Flat spots and ridges or swells in the tyre dramatically increased the dynamic forces on the assembly and greatly accelerated wear.