Broken Rail Research Articles

An experimental study of EMAT ultrasonic surface waves modes in railhead

A lab-based laser-EMAT (Electromagnetic acoustic transducers) system has been developed to observe the ultrasonic surface wave propagation and interaction with surface breaking defects on the sample rail head surface. The frequency- wavenumber dispersion curves of the dominant surface wave modes were determined using 2D-FFT method based on the measurements of the out-of-plane displacement of the surface wave. A complete picture of the ultrasonic surface wave on the sample surface over time was reconstructed with exceptionally high spatial and temporal resolution. Despite the curvature of the rail head, the ultrasonic surface guided wave propagating down the rail is found to have similar properties to Rayleigh waves by direct comparison to those observed on flat samples using the same technique. Rail breaks caused by rolling contact fatigue (RCF) cracks are of growing concern to the modern high speed railway industry (1). The fatigue crack initiates on or very close to the rail rolling surface, which is not related to any material defect. Its occurrence is increasing on high speed passenger lines, mixed and heavy haul railways and can lead to expensive rail grinding in the attempt to remove it, premature removal of the rails and complete rail failure. The rolling contact fatigue damage on rails can be divided in headchecks, squats and spalling. They are caused by a combination of high normal and tangential stresses between rail and wheel, which cause sever shearing of the rolling surface layer of rail head and either fatigue or exhaustion of ductility of material. The microscopic cracks produced propagations through the heavily deformed surface layer of railhead at a shallow angle to the rail running face (about 10 ◦ ∼15 ◦ ) until it reaches a depth where the steel retains its original isotropic properties (2,3). At this stage the crack is a few millimeters deep into the rail head, and usually the crack may simply lead to spalling of material from the rail surface. However, for reasons still not very clearly understood, isolated oblique crack can down into the rail, and if not to detect by ultrasonic testing car, it may cause the rail to break. RCF damages are much more severe from the point of view of the structure integrity for high speed railway track.

AN APPROACH FOR RISK ASSESSMENT OF RAIL DEFECTS

Rail defects appear in a greater variety and frequency due to higher axle loads and increasing traffic density in passenger and freight trains. Many of these rail defects, if left undetected, can develop into rail breaks, which may lead to train derailments. Reduction in the number of such catastrophic events requires huge investments on inspection and maintenance activities. Therefore proper maintenance planning and risk assessment is required to reduce the rail maintenance cost without compromising safety. In this paper, an approach has been developed for risk assessment of rail defects to support the decision-making process during scheduling of rail inspection and grinding frequency, based on the type of defect and its risk of occurring and developing into a rail break. The approach will help in increasing the safety of passengers and rolling stock as well as reducing the overall rail maintenance cost, as it helps in making effective decisions related to inspection frequency (i.e. resource allocation according to the need). The approach is presented with the aid of a case study from the Swedish National Rail Administration (Banverket). Both, quantitative and qualitative analysis technique has been used in this paper to assess the risk of occurrence of a rail defect and its development into a rail break.

Microstructure Features and Contact Fatigue Crack Growth on Rail

Rolling Contact Fatigue (RCF) damage on the surface of rails such a head check, squats is a growing problem. Since rail fractures can cause derailment with loss of life and property, the understanding of rail fracture mechanism is important for reducing damages on the rail surface. In this study, we have investigated RCF damage, fatigue growth and fracture surface morphology on the surface of broken rail using failure analysis and finite element (FE) analysis. The investigation indicates that the crack grows at about 20° to the depth of 8mm from the surface and branches into two cracks. One crack propagates downward at about 47°, the other propagates upward. Since the crack growth rate of the downward crack was faster than that of upward crack, rail eventually was broken. Since the downward branches lead to fracture of the rail, they are more dangerous to the integrity of rails. It has been observed that White Etching Layer (WEL) occurs within the surface of broken rail. It was found that the fatigue crack initiation and propagation was accelerated by WEL.

Introduction to the damage tolerance behaviour of railway rails – a review

Despite substantial advantages in material development and in periodic non-destructive inspection together with periodic grinding and other measures in order to guarantee safe service, fatigue crack propagation and fracture is still in great demand as emphasised by the present special issue. Rails, as the heart of the railway system, are subjected to very high service loads and harsh environmental conditions. Since any potential rail breakage includes the risk of catastrophic derailment of vehicles, it is of paramount interest to avoid such a scenario. The aim of the present paper is to introduce the most important questions regarding crack propagation and fracture of rails. These include the loading conditions: contact forces from the wheel and thermal stresses due to restrained elongation of continuously welded rails together with residual stresses from manufacturing and welding in the field, which is discussed in Section 2. Section 3 provides an overview of crack-type rail defects and potential failure scenarios. Finally the stages of crack propagation from initiation up to final breakage are discussed.

Predicting crack growth and risks of rail breaks due to wheel flat impacts in heavy haul operations

The risk for rail breaks is investigated from mechanical and statistical points of view with particular focus on the influence of impact loads from flatted wheels. For a presumed rail head crack geometry and rail temperature, the stochastic relation between the crack position along the rail and the wheel flat impact position results in a risk of fracture. In addition to the analysis of the risk for final fracture, rail crack growth is also studied. In particular, the contribution of wheel flat impacts on crack growth rates is quantified. The study takes the form of a dynamic load analysis that evaluates rail bending moments due to wheel flat impact. Then, a fracture mechanics analysis is employed to establish stress intensity factors for rail head cracks under bending and temperature loading. These analyses are then combined to give risks of rail breaks and to quantify crack growth rates for varying operational conditions.

Laboratory simulations with twin-disc machine on head check

Head check has been observed at the gauge corner of the high rail in shallow curve tracks for the last several years. Many head checks also develop into breaking out like flaking. Head check with breaking out causes increasing noise and rail breakage. Consequently the interest in countermeasures against head check with breaking out has been growing. Therefore, this paper reports the results of investigations of curved track with head check and laboratory simulations with a twin-disc machine simulated wheel/rail to find out the countermeasures. First, it was identified that head checks were mainly caused on curves whose radii were less than 800 m from analysis of rail inspection data. The high rails of the curved tracks are head hardened rail. Moreover, it was found that lateral forces at high rail of head hardened rail were about 10 kN from track inspection data. Next, laboratory simulations with the twin-disc machine were carried out five times. First laboratory simulation with a HH340 disc whose hardness was the same as head hardened rail was carried out by using the measured data at a curved track with head check. Head check with breaking out finally occurred on the rail disc. After that, laboratory simulations for countermeasure against head check were carried out with standard disc, bainite disc and hypereutectoid disc at the final condition of preliminary experiments. As a result, head check with severe breaking out did not occur on the bainite and hypereutectoid discs over 100 MGT but occurred on the standard disc. Therefore, we can discuss the factors causing head check from these simulations and these results indicate that laboratory simulations for the countermeasure can be performed with the twin-disc machine.

Analysis of tapered, adhesively bonded, insulated rail joints

Adhesively bonded insulated rail joints are used to electrically isolate sections of track into discrete blocks to detect the positions of trains, and are sometimes useful in detecting rail breaks. Recent advances in high-strength rails allow for the use of higher-weight cars. With this increased axle loading of the freight lines, bonded rail joints are encountering early breakdown through either electrical or mechanical failure. Service lives as short as 12-18 months have been reported on some rail lines, significantly lower than the lifetime of other railway components. The cost of replacing the joints has significantly increased the desire for a joint with improved durability. Commercially available bonded rail joints are typically double butt-strap joints consisting of two steel reinforcing joint bars, bonded to the rails with an epoxy adhesive that may contain a fibreglass or aramid cloth layer. This paper investigates a tapered bonded joint that was proposed to reduce the high stresses that can result in the more typical butt-strap joint configuration. The first type of analysis models the rails and joint bars as beams, and the adhesive and ground as distributed elastic springs. Approximate solutions are obtained with the use of the Rayleigh-Ritz method. The finite-element method is used in the second type of analysis. Deflections, bending moments, and stresses are obtained. Based on these analyses, tapered insulated joints should provide some advantages over conventional insulated rail joints, such as lower deflections, bending moments, and shear stresses in the adhesive.

Probabilistic Model for Predicting Rail Breaks and Controlling Risk of Derailment

A model is developed to analyze the risk of derailment of railway vehicles by using a probabilistic approach to model the development of rail defects leading to rail breaks and further to derailment. The risk of derailment is measured by the expected number of rail breaks multiplied by the severity of rail break. To evaluate the risk, four submodels are combined to predict the rate of occurrence of rail defects and breaks. These submodels include one to predict the expected number of weld defects, considering the effect of rail repair; a fatigue model of the rails; and a grinding model to take into account removal of defects through maintenance. The fourth submodel concerns the impact of inspections that are imperfect and of nonconstant frequency. The performance and application of the proposed combined model are illustrated by an example that shows the effectiveness of alternative measures in reducing the risk of derailment. It also shows that the proposed model can be used as a tool for quantitatively evaluating the risk of derailment and for decision making on control of the risk.

Surface wave modes in rails

Rail breaks caused by rolling contact fatigue defects are of growing concern to the railway industry. Very often critical defects cannot be detected reliably by conventional inspection methods. Low-frequency surface waves with a high penetration depth have the potential to overcome such difficulties. In this paper, the properties of surface wave modes in both new and worn rails are investigated and the implications for rail inspection are discussed. The dispersion curves of the dominant surface wave modes were determined up to a frequency of 350kHz using a finite element model and show excellent agreement with experimental data. One surface wave mode was identified to be nondispersive and not significantly affected by cross-section changes due to wear at frequencies above 180kHz. It exhibits a relatively homogeneous energy distribution in the upper half of the rail head and is therefore suitable for inspection purposes. The problem is that there exist several other surface modes with very similar propagation properties. The interference of these multiple modes, which may be generated either directly by the exciter or by mode conversion at defects, means that the received amplitude is position dependent. For this reason, accurate defect sizing will be difficult.

Modelling and analysis of rail maintenance cost

Lubrication at wheel flange and rails on sharp curves is considered as an effective solution for reducing wear loss of material from effective cross-section of rail and wheels. Rail administrations around the world have been increasing axle loads and traffic densities in rail networks. This has led to traffic initiated wear, fatigue initiated surface cracks and rail breaks. Limited research has been carried out on the overall impact of combining lubrication strategies and rail grinding. This paper presents a model for lubrication strategy and rail-grinding interval to reduce wear and rolling contact fatigue (RCF). Data from rail industry is collected and used for numerical illustration.

Decision on economical rail grinding interval for controlling rolling contact fatigue

Rail players around the world have been increasing axle loads to improve the productivity of freight and heavy haul operations. This has increased the risk of surface cracks at curves because of rolling contact fatigue. Rail grinding has been considered an effective process for controlling these cracks and reducing risks of rail breaks. The complexity of deciding the optimal rail grinding intervals for improving the reliability and safety of rails is because of insufficient understanding of the various factors involved in the crack initiation and propagation process. This paper focuses on identifying the factors influencing rail degradation, developing models for rail failures and analyzing the costs of various grinding intervals for economic decision making. Various costs involved in rail maintenance, such as rail grinding, downtime, inspection, rail failures and derailment, and replacement of worn-out rails, are incorporated into the total cost model developed in this paper. Field data from the rail industry have been used for illustration.

Study on centre-fed boundless track circuits

An equivalent circuit diagram for a track circuit with one transmitting end and two receiving ends is presented. Two-port network models are developed under normal, shunt and broken rail modes of operation. Shunt sensitivity and broken rail sensitivity are studied in relation to each of the receivers. An abstract synthesis algorithm is devised and used to determine the optimal end-input impedances. The maximum length of the boundless track circuits of the Sofia Underground is determined.

Ultrasonic vehicle-based rail inspection

Network Rail is working closely with Sperry and First Engineering in trials of a new road rail vehicle that inspects the rail using Sperry ultrasonic track inspection technology, checking for defects and future potential problems. This new machine - the UTU 5 - is said to be much faster, more efficient and more reliable than conventional manual ultrasonic methods. The combination of train-based and road rail vehicle-based ultrasonic inspection systems represents the future for ultrasonic track inspection. According to reports, the introduction of a previous train-based system led to performance and reliability improvements of 40% and a reduction in the number of broken rails in its first year. This article describes Sperry's development of vehicle-based rail inspection and the ultrasonic system employed.

Rail flaw detection: overview and needs for future developments

Rail Flaw Detection has an important part to play in ensuring the safety of the world's railroads. Recent accidents caused by broken rails have focused attention on the technologies that enable the detection of flaws in railroad rail. This paper reviews the technologies currently employed, along with examples of recent field applications. Some of the ongoing advancements and options for the future are also discussed.

Towards a laser-vibrometry technique for measuring railroad rail stress

There is a broad consensus on the need for cost-effective and reliable methods for measurement of axial stress in railroad rails. Constrained thermal expansions and contractions induce large forces which in turn lead to bucklings and rail breaks. We are developing a new method for such measurements, based on the decrease (increase) of effective dynamic flexural rigidity under the influence of compressive (tensile) loads. Scanned laser vibrometry measurements of vibration fields at a prescribed frequency, followed by a comparison with guided wave theory for the complex cross section of the rail, allows the extraction of flexural wavenumbers. These wavenumbers are in turn related to contained load and to the rail’s intrinsic rigidity. Here we report the ongoing status of this work, describing the results of extensive laboratory measurements on unloaded rail, and test-bay measurements on rails subjected to compressive loads to 100 kip.

Book Reviews

Books reviewed:Vincent Bugliosi, The Betrayal of America: How the Supreme Court Undermined the Constitution and Chose Our PresidentJack N. Rakove (ed.), The Unfinished Election of 2000: Leading Scholars Examine America’s Strangest ElectionDaniel Lazare, The Velvet Coup: The Constitution, the Supreme Court and the Decline of American DemocracyAndrew Denham and Mark Garnett, Keith JosephChantal Mouffe, The Democratic ParadoxGerd‐Rainer Horn and Emmanuel Gerard (eds.), Left Catholicism 1943–1955: Catholics and Society in Western Europe at the Point of LiberationLorna Arnold, Britain and the H‐BombJoseph V. Femia, Against the Masses: Varieties of Anti‐Democratic Thought since the French RevolutionGino Bedani and Bruce Haddock (eds.), The Politics of Italian National Identity: A Multidisciplinary PerspectivePaul M. Sniderman, Pierangelo Peri, Rui J. P. de Figueiredo, Jr and Thomas Piazza, The Outsider: Prejudice and Politics in ItalyNorman Birnbaum, After Progress: American Social Reform and European Socialism in the Twentieth CenturyGøsta Esping‐Andersen and Marino Regini (eds.), Why Deregulate Labour Markets?Andrew Murray, Off the Rails: Britain’s Great Rail Crisis—Cause, Consequences and CureChristian Wolmar, Broken Rails

Improvement of border characteristics of jointless track circuit

The track circuit uses the rail as part of the circuit. The purposes of the track circuit are (1) to detect the train, (2) to transmit signals to the train, and (3) to detect rail breaks. There are two types of track circuit. One uses insulation joints at the end of the circuit, and the other is jointless. The insulation joint requires much effort to maintain and control. Furthermore, it is extremely expensive, and uses an insulation material, which is one of the weak points of the rail track. There are some methods for constructing a jointless track circuit, but they have several problems. The biggest one is that the border of the track circuits becomes fuzzy. Another is the interference of multiple track circuit signals. Nevertheless, jointless track circuits have high priority. First, they do not demand an insulation joint and impedance bonds. Second, they are very easy to divide. Jointless track circuits are used for sharp curves where it is impossible to install insulation joints on the Shinkansen line. Also, several conventional lines and private railways use this system. Furthermore, several European high-speed train systems also use jointless track circuits. Regarding Japan Railway, short-distance track circuits for level crossing control are jointless, but normal track circuits have insulation joints, because there is a legal restriction on track circuit border ambiguity. To solve this problem, the author worked out a simple jointless track circuit only with induction coils, whose border characteristics are excellent. Furthermore, it does not have a strong frequency characteristic and it can be applied to any frequency. In this paper, a new type of jointless track circuit is proposed and theoretically analyzed, and basic experiments are reported. © 1999 Scripta Technica, Electr Eng Jpn, 127(4): 64–76, 1999

Improvement of Border Characteristics of Jointless Track Circuit

Track circuit uses rail as a part of the circuit. The purposes of the track ciruit are 1) to detect the train, 2) to transmit signal to the train, and 3) to detect the rail break. There are two types in the track circuit. One adopts insulation joint at the end of the circuit, and the other one is jointless. The insulation joint demands a lot of effort to maintain and control. Furthermore it costs extremely, and it has an insulation material that becomes one of the weak points of the rail track. There are some methods to make a jointless track circuit, but it has several problems. The biggest one is that the border of the track circuits becomes fuzzy. The next one is the interference of plural track circuit signals. Nevertheless jointless track circuit has a big priority. First it does not demand an insulation joint and impedance bonds. Second it is very easy to divide.Jointless track circuits are adopted in the area of the sharp curve where impossible to install insulation joints on the Shinkansen line. Also several conventional lines and private railways adopt this system. Furthermore several European high speed train system also use jointless track circuit. In JR, short distance track circuit for level crossing control is jointless, but normal track circuit has an insulation joint, because there is a law restriction of track circuits border ambiguity. To solve the problem, the author had worked out simple jointless track circuit only with induction coils, which border characteristic is very excellent. Furthermore it does not have a strong frequency characteristic that it can be applied to any kinds of frequencies. In this paper, new type of jointless track circuit is proposed, it is theoretically analyzed, and basic experiments had succeeded that they are reported.

97/03110 Combined (integrated) COREX ironmaking and DRI production technologies

Despite substantial advantages in material development and in periodic non-destructive inspection together with periodic grinding and other measures in order to guarantee safe service, fatigue crack propagation and fracture is still in great demand as emphasised by the present special issue. Rails, as the heart of the railway system, are subjected to very high service loads and harsh environmental conditions. Since any potential rail breakage includes the risk of catastrophic derailment of vehicles, it is of paramount interest to avoid such a scenario. The aim of the present paper is to introduce the most important questions regarding crack propagation and fracture of rails. These include the loading conditions: contact forces from the wheel and thermal stresses due to restrained elongation of continuously welded rails together with residual stresses from manufacturing and welding in the field, which is discussed in Section 2. Section 3 provides an overview of crack-type rail defects and potential failure scenarios. Finally the stages of crack propagation from initiation up to final breakage are discussed.

Dedicated Sensor and Classifier of Rail Head Defects for Railway Systems

Abstract This article presents an original system based on specialized eddy current sensor for the inspection of the railway tracks. The device aims at the detection of broken rails and large head spalls of the rail and it has been designed in order to be mounted underneath automatic driving railway vehicles. In fact, less important types of defects can also be detected. Other uses of the sensor are predictive management of the rail. All the applications need a parametrization procedure of the output signals of the sensor. Then a classification is performed by a set of Neural Networks which is able to split the “defects” into several classes.