Case Study Eschede Train Disaster

Department of Materials Science and Engineering

Case Study

Eschede Train Disaster-1998 March 19, 2011

Authors:

Xiangwan Lai

100207147

Pooja Purohit

100144750

M. Mueed Jamal 100144808 Course:

MAT 6519 Metal Processing and Case Study

Course Tutor:

Dr. Brad Wynne

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Historical Background of ICE The first high speed train in the world was introduced by Japan in the mid-nineteenth century having maximum speed of 186mph. Later on, other countries like Spain, France also participated in building high speed trains. Germany came into competition in late 1980’s and Deutsche Bahn (German Railway Company) introduced the first luxury high speed train ‘Inter City Express (ICE) ’. The first locomotives and carriages were delivered in 1989 and 1990 respectively. On 29 May 1991, the ICE network was officially inaugurated and the first generation Inter City Express (ICE 1) trains were made regularly scheduled in June 1991. [9] Deutsche Bahn has launched three generations of ICE so far. There are currently around 259 trainsets of different versions of ICE vehicles in use. ICE 1 trains, with the highest speed of 280km/h, were deployed in 1991. ICE 2 trains, with the highest speed of 280km/h and each train consisting of only one power head along with seven bogies, were brought in service successfully in 1997. ICE 3 trains are in service from 2000 to present and are having regular service speed of 300km/h. Technically ICE 3 trains can run up to a speed of 330km/h. ICE 3 trains have 67 trainsets and instead of being pulled by locomotives they are having electric multiple units with under floor motors throughout. [9] ICE trains operate all over Germany with connections to neighboring countries. International ICE trains connect Germany with Austria, Belgium, Denmark, France, the Netherlands and Switzerland. Design of ICE high speed trains was very advanced and Amtrak showed interest in buying the ICE design to use on USA rail network. Only after two years of service more than 65,000 people a day used the service. The Eschede train accident in June 1998 was a big setback for German Railway Company and the train destroyed was the first generation ICE trainset 51. There were total 60 trainsets for ICE 1 and 59 are still in regular service. All ICE 1 trains were equipped with two locomotives (power heads) along with 11 to 12 cars, including a restaurant car. Initially monobloc single cast wheels were used for ICE 1 trains. Soon after being deployed, in 1992, a new wheel design (approved by UIC) was passed by Deutsche Bahn for the use in their high speed ICE 1 trains after doing extended test drives. Conventional monobloc wheels were replaced by new type rubber-sprung resilient wheels (type BA 064) for first generation ICE trains, to avoid metal fatigue and vibrations at high speeds. Unfortunately, the new design turned out to be improper, resulting in a failure of one of the rubber sprung dualbloc wheels of ICE 1 (trainset 51) on 3rd June 1998. [9]

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Overview of Eschede Incident On the early morning (5:45 am) of 3rd June 1998, ICE-884 “Wilhelm Conrad Röntgen” with a capacity of around 800 passengers, set off its journey from Munich to Hamburg with 287 passengers on board. ICE-884 was equipped with 18 Rubber-Sprung (type BA 064) and 38 Monobloc wheel sets. After a quick stop in Hanover at 10:30am, the train continued its trip northwards. About 6 km away from village of Eschede, in Lower Saxony, at a speed of 125mph, the wheel tire of the last rubber-sprung wheel on the right side of first carriage broke down. Accompanying a big noise and violent vibrations, a passenger Jörg Dittmann noticed a piece of metal went through an armrest between his wife and son and he reported this to the conductor who was in coach 3. Rather than applying emergency brakes, conductor insisted to see the damage himself, owing to the company policy. Metal piece was the wheel tire peeled away from the wheel body, punctured the floor of first carriage and kept embedded for almost 6km back from the accident site. The embedded wheel tire was hung up directly under the carriage screeching along the rail track making constant damage to it. There were two sets of points (use to change the track of train) on the rail track coming shortly in the way of ICE-884. Just about 3.6sec before the crash, as the train reached the first set of point, the end of the broken wheel tire scooped up the check rail (check rails used to guide railways safely through set of points) and the check rail smashed into the floor of first coach. The strike was massive enough to cause derailment of the two wheels in the rear of coach 1. At that stage if the train still could have been stopped by emergency brakes, the derailment might not had turned into a big catastrophe. Train continued to move on with the speed of 125 mph and one of the derailed wheels hit the switch of the second set of point and opened them. That caused the switching off the coaches, following carriage 1, to the local branch line parallel to main line. Sudden switching off the track of train at a high speed resulted in disconnection of the front power head from rest of the train. As a consequence of this 3rd carriage smashed into a fragile pier of a nearby 300 tons road bridge due to which the bridge collapsed and fell onto the rear half of coach 5 and restaurant coach 6, destroying them completely. The coach 4 derailed by the big vibrations of coach 3, went down the track and killed 2 Deutsche Bahn workers nearby. Seconds before this collision, Jorg Dittmann was just going to show the conductor that a big metal piece has punctured through the floor of first passenger coach; but they already took precious time coming from coach 3 to the coach 1. Conductor did not see the damage and the brakes were not applied and eventually the accident occurred at 10:59 am local time. The collapsed bridge completely blocked the track and subsequent remaining coaches 7 (service car), 8th and 9th, first class coaches (10-12) and rear power head all derailed and jackknifed into the pile. By 11:07am, the police declared a “major emergency” and more than 1000 rescue workers were sent to the crash site. [7][9] Eschede train disaster is the worst high speed train accident in German history, after World War 2, with 101 people killed and 88 people injured.

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Figure 1 Eschede train disaster

Description of the actual reason of the failure Although many critical issues, explained later in this case study, were involved in the incident which led to the catastrophic failure of a first generation ICE 884 “Wilhelm Conrad Rontgen” on 3rd June 1998, but, the main reason of that failure, after the trial of the incident was found as metal fatigue; and is still considered as the root cause of the failure. At the speed of 125 mph ICE 884, while on its way to Hamburg from Munich, was passing through the village of Eschede, when the last wheel on the right side of the first bogie suffered from a fatigue crack, causing devastating results. ICE 884 was equipped with mono bloc wheels as well as rubber-sprung wheels. The fractured wheel was a dual bloc rubber-sprung resilient wheel type BA 064. Generally these Rubber-Sprung wheels consisted of a steel wheel disc (inner wheel rim having a hole for shaft), a steel wheel tire (outer wheel rim) and a number of rubber pads, sandwiched between wheel disc and wheel tire, to minimize the noise problem. It was the outer rim, the wheel tire made of steel, which was broken when a fatigue crack finally propagated through the wheel tire causing the deadliest fast speed train accident in the world. The crack was originated near the center of the inner surface of the wheel tire which contacts the rubber block and where the highest stress level in the wheel tire was located. Fatigue failure occurred, even at low mean level stress, because of the extra thinning of the wheel tire. [1] Fatigue is known as a single cause which can lead to failure of metals, polymers and some ceramics as well, with glass as the only exception. In metals particularly iron based alloys it is a common issue for the fractured surfaces. The applied stress which can lead to fatigue failure may be axial (tension-compression), flexural (bending), or torsional (twisting in nature). Different stress-time modes are possible regarding to fatigue. In a reversed stress cycle amplitude is symmetrical about a mean zero stress level, for example, alternating from a

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maximum tensile stress (σ max) to a minimum compressive stress (σ min) of equal magnitude. In another type, known as repeated stress cycle the maxima and minima are asymmetrical relative to the zero stress level. For this case the stress level alternates about a mean stress σ m, defined as the average of the maximum and minimum stresses in the cycle, i-e σ m = (σ max + σ min )/2

There is a range of stress σ r which is just the difference between σ max and σ min; σ r = σ max - σ min

Stress amplitude σ a is just one half of this range of stress, or σ a = σ r /2

Another term stress ratio R is just the ratio of σ min and σ max. R = σ min / σ max

Figure 2 Repeated Stress Cycle [5]

The fatigue properties of a material can be determined now on laboratory scale using a test apparatus, shown below, which should be designed to duplicate as nearly as possible the service conditions (stress level, time, frequency pattern, etc)

Figure 3 Fatigue Testing Apparatus for making rotating-bending tests [5]

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Using above apparatus compression and tensile are imposed on specimen simultaneously as it is bend and rotated. Results from the test can be plotted as stress S and the logarithm of the number N of cycles to failure for each of the specimens used, as shown below. For most of the ferrous alloys the S-N curve becomes horizontal at a higher N values, which is the limiting stress level, called the fatigue limit. This fatigue or endurance limit is a limit below which fatigue failure will never occur. For many steels, the fatigue limit range between 35% and 60% of their tensile strength. Fatigue strength is the stress level at which failure will occur for a specific number of cycles (N) and the number of cycles required to cause fatigue failure at a specified stress level is known as fatigue life N f . At higher stress levels low cycle fatigue will occur (104 to 105 N) and at lower stress levels high cycle fatigue, greater than about 105 cycles, occurs normally. [5]

Figure 4 S-N Curve typically for ferrous based alloys (steels) [5]

Fatigue occurs following the crack initiation, crack propagation and finally the failure or tearing apart of material’s surface. Fatigue fracture surface has two types of markings beachmarks (macroscopic) and striations (microscopic). Beachmarks are formed when interruptions to crack propagation stage occur, representing the period of time over which crack growth occurred. Striations represent the advance the advance distance of the crack front during a single load cycle. [5] The typical fatigue crack markings on the surface of the fractured wheel, type BA 064, of ICE 884 is vivid in the image below:

Figure 5 Fracture surface of a broken wheel tire (showing typical fatigue failure) [1]

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Issues linked with catastrophic failure

Inadequate design of Rubber-sprung resilient wheels Initially the 1st generation ICE trains were equipped with the single cast mono bloc wheels. These wheels are a single assembly made of steel and are much stronger and long life wheels. On the other hand the rubber-sprung wheels, of type BA 064, which were used for ICE 884 later on, are a dual bloc wheel. This wheel consists of a wheel tire, 34 rubber pads (20 mm thick), an inner wheel disc and a solid shaft. Wheel rim for this type of wheel is divided into two parts, a central wheel disc and an outer detachable wheel tire. Rubber pads are pressed between wheel tire and disc, while they are both bolted together. Due to the presence of rubber pads the wheel tire has to be made thin. Highest stress level on the tire can be found on the inner side of the wheel tire where it makes contact with rubber pad. Design of this new type of wheels was clearly having flaws in it. It was made to overcome the problem of fatigue, noise and vibrations at cruising speeds; but this design resulted in fatigue failure. [2]

Figure 6 Rubber Sprung Wheel (type BA 064) Design & Flaws [4] [8]

As a result of rotation of the wheel, cyclic loading can be observed in the wheel. The thickness of already thinner wheel tire reduced much quickly because of the intense cyclic loading caused by resilient rubber pads sandwiched between a two parts steel rim. As the train travelled, the inner wheel disc also worn out and its diameter reduced which caused further severe dynamic and cyclic loadings on the wheel tire making it thinner and weakened it. This resulted in increasing the stress amplifications on a single point on the inner side of wheel tire, from where the crack initiated and finally propagated to cause failure. This fracture occurred at relatively low fatigue mean stress level as the cross section of wheel tire was reduced up to

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dangerous limits. [2]Also thermal expansion co efficient of rubber is much less than steel, hence the rubber could not have expanded while heated. This added the stress on wheel tire. Approval of Inadequate Rubber-Sprung Wheels Deutsche Bahn DB, the German railway company at that time, employed the new designed rubber-sprung resilient wheel for the use in ICE-1, without following the sufficient testing procedures. The design was approved by UIC (International association of railways) and for the type of rubber-sprung wheel there was no special guidance or standard at that time. DB engineers also did not perform any adequate fatigue testing for the wheels type BA 064 and sent them into service after extended test drives, for use at 280km/h. [1] [7] Poor Operational Testing/Inspection Procedures During the operational modes of ICE 884 WCR methods employed to test the rubber-sprung wheels were inadequate and poor. The engineers of DB used to check the macro level cracks with a flash light. For micro level cracks no useful method was employed that time other than a high tech technique coming up with results having constant errors in them (ultrasound technique). Hence, engineers were unable to detect the cracks inside the wheel tire or disc. Also no equipment was present that time to perform the complete fatigue test (crack initiation, propagation and failure analysis) while the train was operational. Tread Diameter Minimum Limit Set Experts of Fraunhofer Institute expressed their concern that metal fatigue could lead to wheel rim failure. Experts warned that wheels should not be operated if worn out to levels below 880mm of their tread diameter. Even then DB set the minimum limit for the tread diameter as 854mm. New wheels had a tread diameter of 920mm and the wheel that fractured was having a tread diameter of 862mm. [4].Given below is the table containing data related to that fractured wheel: Table 1: History of ICE 884- Rubber Sprung Wheel which got fracture [1]

Different Notifications Pointing Out Defected Wheel In July 1997, the company that runs the network of Trams in Hanover, detected dangerous metal fatigue cracks occurring in their dual bloc resilient wheels; even though trams were operated at the speeds of only 24 km/h .Only months before the incident Tram company notified Deutsche

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Bahn with this problem. But DB did not perform any checks for they were not having any problems of metal fatigue in the wheels of their trains. When the maintenance report was downloaded from the crash train onboard computer, another, vital information was revealed. It was found that, two months before the incident, conductors of train forwarded about eight separate complaints about the unusual noise and vibration coming from the carriage which had the wheel that fractured. Just week before, the wheel that got fracture was highlighted as being defected in three separate automated checks. In spite of all these warnings the fractured wheel was not replaced and it took the lives of 101 people after getting a sudden fatigue failure. [7] Strict Company Policy Had the emergency brakes been applied immediately after the derailment of train, or tearing off the floor of first bogie by broken tire, ICE 884 might had stopped before hitting into the bridge; and many lives could have been saved. But, owing to the strict policy of DB Company emergency brakes can only be applied after the conductor/manager views the damage or know the cause of stopping the train himself. The man who saw the metal piece tearing the floor of carriage went to call train conductor rather than applying emergency brakes himself and hence time was wasted. Conductor was about to see the damage in first carriage, when the train collided into the bridge with a catastrophic incident. Poor Bridge Design & Set Point Location The Bridge into which ICE-884 hit at the speed of 125 mph was not supported by strong spans anchored to solid abutments on either side, it was in fact supported by just two thin piers. Also the location of railway track set points (used to change the track of train) was in proximity to the bridge that caused the accident turning into a big disaster. [4] Other Related Issues Rescue workers found it very difficult to find a way to trapped passengers inside the train, as they took a lot of time to cut through the rigid aluminum frames and pressure proof glass windows. Also the passengers were not able to come out by breaking the windows. The welded parts of carriages were unzipped in crash and resulted in almost complete destruction of some of the carriages of ICE-884 ‘WCR’.

Engineering Systems Failure As already explained in the issues above the following engineering systems associated to them failed:

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Design System Failure The BA 064 type rubber-sprung wheels used in ICE-884 had various limitations and were not appropriate to be used on high speed ICE trains. Reduction in wheel tire and its increased flexing resulted in increased bending stress that ultimately led to the fatigue failure. Also incorrect selection of tread diameter contributed to design system failure. Construction System Failure Poor road bridge/overpass design and the proximity of railway track set point to the bridge, led to the construction system failure. Also the welded carriages which were not having enough strength unzipped in the accident; and the pressure proof windows, with no break points, made it difficult for the rescue team to reach the passengers entrapped. Hence it was another engineering system failure. Quality Control & Inspection System Failure Inadequate, poor and insufficient wheel testing methods, which could not detect the internal flaws (cracks) of the wheel tire, eventually facilitated the failure. Others System Failures Flawed emergency operating procedures of Deutsche Bahn was also interlinked with the accident of ICE-884, and made it a disaster. As the speed of train when the wheel was broken was very high; and it remained the same until it collapsed into the bridge. No emergency brakes were applied immediately to stop the train, after the wheel was broken!

Presently bridge design has been improved. Set point locations have been re profiled. Glass windows for ICE trains are now having points through which passengers can break out in time of emergency. In our opinion the engineering systems that time should have been made so as to ensure no failure of the train that could have led to big disaster. Firstly the engineering design system should had new specifications particularly for the new dual bloc rubber sprung wheel design. This could only be possible that time if the testing engineering system could have been able to approve the design specifications by appropriate testing techniques. XRD techniques should be used instead of Ultrasound testing devices to detect cracks, as the former are far more accurate. Bridge design, which falls under civil engineering system, should have been a superior one and must had strong support of adequate strength to carry 300 tons of its weight. Manufacturing system for ICE trains should have been so that train carriages could not have unzipped during crash; and also the windows might have easily broken to ease rescue operations.

CONCLUSION The fracture of the wheel tire that brought the accident of ICE-884 was caused by a fatigue crack, which finally propagated at a relatively low mean stress due to reduced cross section of tire. As the thickness of tire reduced, point load and the bending stress on it increased; and

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intense flexing of tire resulted in fatigue failure of tire. Fretting might have participated in lowering the fatigue limit of the wheel tire material as it was in contact with a rubber pad from the inner side; but, research results had showed that no fretting damage was observed on the inner side of tire where the crack initiated. It was found that rubber contact had no affect on fretting fatigue strength. Finite element method of testing FEM has showed that crack initiation site was at a point, present on the inner side of wheel tire, where the maximum stress (hoop stress) was located. [3] No pre existing flaws, which could have facilitated the crack initiation, were found in the broken wheel tire after the testing. Crack must have initiated therefore due to some other reason. At the time when wheels were employed no individual UIC guideline existed for wheel type BA 064, it was a completely new design; and hence the design specifications for monobloc wheels issued by UIC that time were followed for rubber-sprung wheels. No cracks were found for approximately 100 wheels that had been taken out of service before accident. For almost 5000 wheels removed after the accident, were having cracks in tires but no pre existing flaws were found. Many of these wheels were having larger diameter then the broken wheel and since the cracks in them never reached a critical depth; thus this supports the assumption of generally a very low mean loading level being acted on wheels. Also these results supported an assumption of a rare or singular event that could have initiated the crack. [1] In spite of all the testing done which apparently showed the only culpable for this accident as fatigue; nevertheless Deutsche Bahn, after getting all the warnings which pointed out the defected wheel which eventually got failure, did not replace the wheel. Also it could have been possible to have computational stress analysis using simple models that time, which could have revealed that the wheel type BA 064 which failed was too thin, before the accident. The extended fatigue failure only occurred when the cross section of wheel tire dropped down to 20% of its original. [1] However the accident was proved to be naturally violent. Now Deutsche Bahn has complete facility for proper testing of fatigue. They have Mechanized Inspection Systems based on ultrasonic and eddy currents technique. These systems include system AURA (examines the wheel set that is dismantled from the train and after re profiling) and system UFPE (examines the wheel set in the bogey under the train and after extensive usage). [6] Within a week after the accident all the rubber-sprung wheels were changed with the conventional monobloc wheels. Two engineers of Deutsche Bahn and an employee of wheel manufacturing company were accused of negligence homicide after a trial began in August 2002. In the end of trial, engineers were fined around 10,000 Euros but no one was considered guilty for the negligence homicide. Deutsche Bahn paid 30,000 DEM to the families of dead ones for each person killed. [7] Had the testing procedures and facilities been superior that time, there might have no loss for the company as well as for the families of 101 people that died.

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References [1]

V. Esslinger, R. Kieselbach, R. Koller, Bernhard Weisse The railway accident of Eschede – technical background Engineering Failure Analysis, 2004, 11, 515–535.

[2]

H.A. Richard, M. Fulland, M. Sander, G. Kullmer Fracture in a rubber-sprung railway wheel Engineering Failure Analysis, 2005, 12, 986–999.

[3]

M. Kubota, K. Hirakawa, The effect of rubber contact on the fretting fatigue strength of railway wheel tire Tribology International, 2009, 42, 1389–1398.

[4]

S. Wander, Derailed System Failure Case Studies NASA, 2007, 1, Issue 5.

[5]

W. D. Callister, Jr Materials Science and Engineering an Introduction - sixth edition, 2003, Jhon Willey and Sons, New York, 211-221

[6]

S. Schuhmacher, H. Maly, R. Ettlich, Deutsche Bahn AG Dynamic Inspection of High Speed Train Wheels, Proceedings of the Seventh International Conference on Maintenance and Renewal of Permanent Way, Power and Signalling, Structures and Earthworks, July 2004.

[7]

Eschede Train Disaster, World News, http://wn.com/Eschede_train_disaster, accessed on 12. 03.2011

[8]

R. A. Smith Railways and Materials: synergetic progress, Iron and Steelmaking, 2008, 35, 511-513.

[9]

Wikipedia, http://en.wikipedia.org/wiki/Eschede_train_disaster, 16.03.2011