Elsevier

Engineering Failure Analysis

Volume 35, 15 December 2013, Pages 66-81
Engineering Failure Analysis

Axle fracture of an ICE3 high speed train

https://doi.org/10.1016/j.engfailanal.2012.11.008Get rights and content

Abstract

In July 2008 an ICE3 high speed train rated for 330 km/h service speed derailed during departure from Cologne, Central Station, Germany, due to fatigue failure of one of the driving axles. The train was emergency stopped immediately and, due to low travel speed at this point, no serious injuries occurred to passengers. Referring to public interest, the public attorney’s office solicited the German Federal Institute for Materials Research and Testing (BAM) for the analysis of the root cause.

No deviations from specification were found in the geometries of the basic parts of the bogie or the wheelset assembly. Inspection of the axle fragments using standard acoustic non-destructive testing (NDT) techniques revealed no additional cracks and no indications of oversized discontinuities. Metallographic and chemical inspection of the axle material and its microstructure revealed all parameters to be acceptable except for an elevated impurity level.

The fracture surfaces of the axle fragments were heavily damaged due to some continued travel after final breakage on the high speed line before Cologne Central Station. Extensive visual inspection of the remaining beachmarks was carried out to find the origin of the fatigue crack. The region of the crack origin was located near the axle surface but could not be analysed in detail due to secondary damage. Fatigue was identified as the mechanism of crack growth until final fracture, but the reasons for crack initiation initially remained unclear.

Neither standard NDT techniques nor metallography according to the relevant axle specifications were able to identify inclusions in the material that could have served as crack initiation sites. However, discontinuities were detected near the crack origin in micro computer tomography and ultrasonic immersion testing. Subsequent metallographic sample preparation was targeted to specific areas based on the location coordinates of the flaws identified by these NDT techniques. These revealed non-metallic inclusions that were much larger than admissible for the relevant specifications. It is likely that the fatigue crack in the highly loaded axle volume initiated at those non-metallic inclusions.

Highlights

► We analysed the causes for the axle fracture of the German high speed train ICE3 in 2008. ► Due to severe damage of the fracture surfaces NDT had to be used to find crack initiation. ► Fatigue crack initiated subsurface at non-metallic inclusions (NMIs) in high strength steel. ► New combination of non- and destructive methods for the detection of NMI is presented. ► We provide recommendations on improvement of railway axle safety.

Introduction

The German high speed train ICE3 is approved for a top speed of 330 km/h. First public service took place in late 2000. Deutsche Bahn (DB) operates a fleet of 63 ICE3 trains. On 9 July 2008 one wheelset of the powered bogie of a trailer vehicle, Fig. 1, derailed just before crossing the Rhein bridge at Cologne Central Station, Fig. 2. Since the train travelled at very low speed at this moment, fortunately there were no injury to persons and only minor damage to the rail track. The train previously came from the high speed line and changed travelling direction in Cologne Central Station as scheduled.

The cause for the derailment of the wheelset was the previous fatigue fracture of the hollow axle, Fig. 2, at the T-notch, Fig. 3.

Because of public interest, the public attorney’s office solicited BAM’s analysis of the root cause. The task for BAM was to look for deficiencies of the material, manufacturing and service of the wheelset, defects of the vehicle and compliance with standards.

The failure case was investigated by the authors of the present paper and documented in detail [1] and in extracts [21].

The in-service ultrasonic testing (UT) inspection interval for this type of driving axle was 300,000 km. Last non-destructive testing (NDT) using mechanized UT of the hollow axle took place in March 2008, 150,000 km before fracture: according to the operator DB no crack-type indications were recorded at this time. During UT in-service inspection on crack type defects at the outer surface the recording level was set to approx. 2 mm saw cut depth (SCD) [21].

A few days before the axle fracture, the wheelset and its axle were inspected visually by the operator DB, without any indications recorded.

The final fracture occurred when the axle was in service ∼3 million kilometers which refers to ∼109 revolutions. Regarding the load cycles, this belongs to the very high cycle fatigue (VHCF) range.

DB operates a large number of temperature sensor systems positioned at the track for detection of elevated temperatures of wheelset bearings and brakes of passing trains. The systems installed at the high speed line to Cologne are able to measure the temperatures in trains travelling at 300 km/h for each axle separately. This way it was possible to detect and record that only the axle concerned (cp. Fig. 1) showed unusual high temperatures. This was recorded first about 50 km before Cologne.

Section snippets

Investigation of components and axle material

Mechanical fracture of a component, in principle, occurs when the applied stress is higher than the strength of the material either for static or cyclic loading.

The first task is to check if the loading of the failed axle was in the range of all other axles (∼1200 driving axles in the ICE3 fleet [36], [37]) that survived the same in service time without fracture (∼1/3 of all driving axles), Section 2.1.

If this could be affirmed, the second task would be to check whether the strength of the

Origin, effect and detection of non-metallic inclusions

In some previous failure cases, investigators were successful in detecting and documenting non-metallic inclusions as fatigue crack starter on fracture surfaces [2], [3] e.g. of a big crankshaft made from a similar high strength tempering steel [4].

In order to understand the role of non-metallic inclusions and to verify their contribution to the root cause of the ICE3 axle fracture, their origin and effect was investigated in more detail. Within a literature review the influence of non-metallic

Root causes for axle fracture and failure sequence

Coming back to the initial failure analysis of the high speed train axle fracture, the results of the survey of components, Section 2.1, material testing, Section 2.2, and the investigation of the crack initiation area, Sections 2.3 Fractography, 2.4 Crack initiation: micro computer tomography and metallography, now need to be combined for identifying the root cause(s) of axle fracture [1], Section 4.1. The chronology of crack initiation, growth and time of final fracture of the axle is

Immediate measures

Immediately after the fracture, all ICE3 trains were stopped by the German Federal Railway Authority (EBA). The UT inspection interval for all hollow driving axles made from this and similar high strength steels was reduced from 300,000 km to 60,000 km and further to 30,000 km in October 2008 [31].

EBA 2008 also decided to significantly reduce the inspection intervals for German trains with axles from similar high strength steels as the 67 ICE-T trains with tilting technology and the S-Bahn Berlin,

Acknowledgments

The authors cordially thank S. Bohraus for his enduring microfracto- and topographic work, J. Goebbels, D. Gohlke and T. Heckel for their intense search for inclusions using μCT and UT immersion technique, B. Bogel and O. Paulinus for their careful metallographic target preparations and purity assessment, R. Häcker and B. Abbasi for preparation and testing of specimens as well as standards research, R. Saliwan Neumann for the EDX analysis of inclusions and the other colleagues of BAM failure

References (38)

  • G. Murtaza et al.

    Empirical corrosion fatigue life prediction models of a high strength steel

    Eng Fract Mech

    (2000)
  • Y.B. Liu et al.

    Dependence of fatigue strength on inclusion size for high-strength steels in very high cycle fatigue regime

    Mater Sci Eng A

    (2009)
  • J. Ma et al.

    Effects of inclusion and loading direction on the fatigue behaviour of hot rolled low carbon steel

    Int J Fatigue

    (2010)
  • E. Pessard et al.

    Modelling the role of non-metallic inclusions on the anisotropic fatigue behaviour of forged steel

    Int J Fatigue

    (2011)
  • U. Zerbst et al.

    Fracture mechanics in railway applications – an overview

    Eng Fract Mech

    (2005)
  • Expert report of federal institute for materials research and testing (BAM). Gutachten BAM-V.3/566. Schadensanalyse an...
  • G. Lange

    Technische Schadensfälle

    (2001)
  • Erscheinungsformen von Rissen und Brüchen metallischer Werkstoffe. Verlag Stahleisen;...
  • Bargel HJ, Schulze G. Werkstoffkunde. Berlin, Schroedel, 1978, S. 359–360 based on: Wohler, H. Prüfbericht 1.2/11323....
  • Cited by (0)

    View full text