On the accident was attributed to fatigue. It

 On themorning of June 3, 1998, ICE train 884, the “Wilhelm Conrad Rontgen” (WCR),consisted of a single locomotive pulling 12 cars, including passenger coaches,buffet car, service car and a rear locomotive derailed about 6km outside ofEschede, in Lower Saxony. A total of 101 people lost their lives and 200sustained injuries. The cause of the accident was attributed to fatigue. It wasnoted that the stress caused by the wheel rims being flattened into an ellipsewith each revolution up to (500000 times a day) resulted in development ofcracks inside the wheel rim leading to failure. The thinning of the rimexaggerated dynamic forces causing micro cracks to grow larger.

After theaccident, all ICE operations were suspended pending the outcome of the fullinvestigation. Consequently, the wheel-tire design was completely discontinuedthroughout Germany and was replaced by a mono-block wheel design. Charges ofmanslaughter were brought against two Deutsche Bahn officials and one engineerin August 2002. Financial settlements were made in April 2003 after courtbattles which lasted at least 53 days. Aerial view of the derailed train isshown in Appendix C.Preliminary LiteratureSurveyAdhesionContact TheoriesWheneverwe travel, the vehicle we are riding in will speed up and slow down severaltimes during the course of the journey.

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Manoeuvres like these require force andtrains in particular need to generate a lot of tractive force in order toovercome rolling resistant. A rail wagon typically carries a load of about 10tonnes and this load rests on a small area roughly 10mm across. The pressuresat this interface are very high and considerably in excess of the normal yieldstress of the material. Generally, there are two types of contacts namelyConforming and Non-Conforming contacts. When surfaces of two bodies fit exactlyor even closely together without deforming they are regarded as conforming.Typical examples of conforming bodies include flat slider bearings and journalbearings. On the other hand, bodies which have dissimilar profiles are said tobe non-conforming.

A schematic representation of non-conforming bodies is shownin Appendix D. HertzSurfacesof Engineering components are frequently subjected to contact loading wherelarge stresses are applied over highly localised areas. According to (N. P.Padture) these kinds of loading configurations in the elastic limit are typifiedby Hertizian contacts. Between 1886 and 1896 Hertz published two articles whichformed the basis of what is now known as the field of contact mechanics. Hertzinvestigated the case of deformation of elastic bodies of different curvatures.These non-conforming bodies, such as a sphere, indenting a flat plane or a pairof cylinders in cross contact configuration make an idealised point contactwhen brought to touch each other (Vasilis Votsios, 2003).

As load is appliedto the target surface the point of contact grows, with the increase indeformation on the surfaces in contact.  Hertz theory enables one to calculate theshape of the area of contact and magnitude of distribution of normal andtangential stresses on the surface of contacting bodies. There are five typesof commonly used solutions, and these shall be discussed in more detail in thebody of the main report. For the purposes of this submission the model ofcontact between two spheres from which contact mechanics between the rail andthe wheel is based shall be discussed.

For contact between two spheres of radii R1 and R2,the area of contact is a circle of radius a, as showed in Appendix D.Rollingcontact defectsWearSquats,Squats are surface or near surface initiatedrolling contact fatigue defects. They are sometimes referred to as “darkspots”. These types of defects occur in areas of unsteady rolling contact.These typically include areas with transition curves, turnarounds, and welds,regions of braking and acceleration and areas with unsupported slippers. Thesetype of defects are characterised by cracking which initiates on the rail surfacegrowing to a depth of about 3-6mm below the surface.

The rail surface becomesdepressed and a dark patch as seen in Appendix E.Wheel burns,These are defects that form on the runningsurface of the rails and generally occur in pairs directly opposite oneanother. They are caused by continuous slipping of the locomotive or tractionwheels on the rails, which occur when longitudinal creepage between contactspoints of the wheels and the rails reaches saturation. The slipping action ofthe wheels has the effect of increasing the surface temperature of the wheelbeyond the transition point and on cooling the rail material undergoes abrittle transition into a martensitic phase resulting in crack formations asdeep as 6mm.

Rolling Contact Fatigue.Rolling contact fatigue is considered one ofthe leading causes of failures of rail track and train wheels. As mentionedearlier in the report, fatigue had led to a heavy loss in life and companiesresponsible have suffered heavy penalties. Fatigue in rail terms occurs onrails or wheels due to exposure to repeated dynamic loads which cause microcracks or defects to grow to a critical size over time and consequently leadingto failure.

  Repeated loads cause anincrease in internal stress which gradually work harden steel until it’sbehaviour is purely plastic until leading to damage. An example of fatigue wear is shown in Figure 1.Figure 1. Fatigue Failure on rail head and Fatigue cracks on wheel (Anders Ekberg, 2014)A lot work has been carried out in the pastfew decades to try and combat fatigue related problems on permeant ways.

Despite this, catalogued field observations of the extent, development and rateof fatigue occurrences and wear rates on rail lines are still sparse. A betterunderstanding of both wear and fatigue phenomena is required in order thatimproved ways of eliminating  the issuecan be achieved. In situations where crack initiation is unavoidable, theprogress of cracking need to monitored carefully using appropriate engineeringtechniques and early intervention methods such as grinding and welding need tocarried out before critical growth levels are reached. Corrugations.Corrugations are type of defects which occuron the running surface of the rail in form of wave-like patterns which show upas long pitch and short pitch form. Long pitch corrugations form about 300mmlong wave lengths and generally develop under high axel load above 20 tons.

Thedepth of the waves can range from 0.1mm to above 2.0mm. Plastic flow ofmaterial with long pitch corrugation occurs on the rail head due to excessivecontact stresses and vertical resonance of unsprung mass on the track. This canbe seen in Appendix F.

Short pitch corrugations generally develop under lighteraxel load below 20 tons synonymous with passenger operations and are usually ofdepth below 0.3mm and exhibit 30mmm to 90mm wave lengths. It isthought that short pitch corrugations form from the differential wear caused by acyclic longitudinal sliding action of the wheel on the rail, either during theacceleration, braking phase and lateral motion across the rail.

Proposed Approach andMethodologyIt is proposed that the delivery of the project shall beundertaken using approaches highlighted in following gateways:Stage 1: Review literature on the followingaspects•     History of rail accidents due to fatigue failure•     Non-linear steady state FEA analysis


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