Gauge Corner Cracking Research Articles

A study on the countermeasure method for gauge corner cracking by applying the worn profiles of rail

A study on the countermeasure method for gauge corner cracking by applying the worn profiles of rail

Proposal of the rail profile selection method to reduce gauge corner cracking initiation by mitigating contact conditions of wheel and rail

Proposal of the rail profile selection method to reduce gauge corner cracking initiation by mitigating contact conditions of wheel and rail

A study on rail profile for countermeasure of gauge corner cracking

A study on rail profile for countermeasure of gauge corner cracking

A Study on prevention measures for gauge corner cracking

A Study on prevention measures for gauge corner cracking

Studs and squats: The evolving story

Several railways suffer from a defect that has been christened a “stud”, which appears superficially similar to a squat but is very different in character. Although both initiation and propagation of studs are poorly understood, at least a couple of railways have already benefitted from exploiting the less malevolent nature of studs, particularly the fact that these do not themselves initiate transverse defects.This paper is based primarily on field work undertaken in NSW to reveal some of the characteristics of stud defects, in particular in contrast to rolling contact fatigue (RCF) of which squats are a classical example. This work has been supplemented by a very much smaller sample of field work undertaken in Switzerland and metallurgical analysis of studs that was undertaken at Sheffield University of samples from Swiss Railways. Studs are often associated with sites where there is high traction, such as the exit from stations. In NSW they commonly initiate at about 10–20° to the vertical towards gauge on the high rail in curves, then grow into the rail at an angle of about 20° to the rail surface. Studs can at first develop very quickly e.g. to a depth of 2.2mm in 6MGT. The stud fans out across the rail from the initial surface crack, developing across the rail at a substantially constant depth of 3–6mm. If the stud is left, it may rise to the surface at the opposite side of the railhead, giving rise to an ugly spall with a fracture surface typical of a conventional fatigue crack. There is no evidence whatsoever that studs become transverse defects, nor should this occur with a crack that develops across rather than along the rail as there is an absence of flexure to drive the crack. Studs have grown in rails in which there is no significant plastic work, and accordingly also no significant depth of compressive residual stress. These characteristics are not those of a classical squat.Although some transverse defects (TDs) have been associated with studs, both gauge corner cracking (GCC) and studs have coincided in all of the cases examined. In these cases the TD has clearly developed in the conventional and well understood manner from the GCC. The stud has given rise to a dynamic load that accelerates growth of the TD. But if the GCC had not existed, the TD would not have developed.The paper provides some guidance on treatment and maintenance of studs as well as updating a hypothesis that still rests substantially on circumstantial evidence. It is strongly recommended that railways move away from referring to these defects as “squats”, particularly when it is clear (as is increasingly the case) that the defect described is not a squat.

Microstructural characterisation of rolling contact fatigue damage in flashbutt welds

The development of premium heat treated rail steels with hardness levels of 400HB and above, and the application of these under high axle load conditions, has provided substantial improvements in rail lives. An additional benefit is the potential to increase the intervals between consecutive grinding cycles, where rail grinding is used to control rolling contact fatigue damage. Increased grinding intervals will, however, place more emphasis on the performance of rail welds which are more sensitive to localised rolling contact fatigue damage than parent rail. The increased sensitivity to damage at welds arises from the inherent variability in material characteristics, and may vary between welding procedures, and for any particular welding process, between rail grades.A detailed microstructural examination of the characteristics associated with flashbutt welds in the new condition and after exposure to service conditions which resulted in gauge corner cracking has been performed in order to correlate the development of rolling contact fatigue damage to the underlying microstructure. Of particular interest were the behaviour of the softened (heat affected) zones and the role of grain boundary networks of pro-eutectoid cementite which may develop during welding of hypereutectoid rail steels. Understanding the effects of these microstructures on the material response to wheel rail contact conditions, and using this information to develop improved welding procedures or modifying rail maintenance procedures to minimise their effects, are necessary in order to maximise the benefits obtained through use of these rail steels.Gauge corner cracking was found to initiate in the softened zone associated with spheroidised microstructure. The role of pro-eutectoid cementite network on crack initiation was difficult to evaluate, however, it seems to have only a minor effect on crack propagation. The proposed options to mitigate gauge corner cracking was to make narrow welds to minimise softened zone or to select rail grades that are more resistant to spheroidisation.

Railroad inspection based on ACFM employing a non-uniform B-spline approach

The stresses sustained by rails have increased in recent years due to the use of higher train speeds and heavier axle loads. For this reason surface and near-surface defects generate by Rolling Contact Fatigue (RCF) have become particularly significant as they can cause unexpected structural failure of the rail, resulting in severe derailments. The accident that took place in Hatfield, UK (2000), is an example of a derailment caused by the structural failure of a rail section due to RCF. Early detection of RCF rail defects is therefore of paramount importance to the rail industry. The performance of existing ultrasonic and magnetic flux leakage techniques in detecting rail surface-breaking defects, such as head checks and gauge corner cracking, is inadequate during high-speed inspection, while eddy current sensors suffer from lift-off effects. The results obtained through rail inspection experiments under simulated conditions using Alternating Current Field Measurement (ACFM) probes, suggest that this technique can be applied for the accurate and reliable detection of surface-breaking defects at high inspection speeds. This paper presents the B-Spline approach used for the accurate filtering the noise of the raw ACFM signal obtained during high speed tests to improve the reliability of the measurements. A non-uniform B-spline approximation is employed to calculate the exact positions and the dimensions of the defects. This method generates a smooth approximation similar to the ACFM dataset points related to the rail surface-breaking defect.

Squats and squat-type defects in rails: the understanding to date

In the 1970s, a rolling contact fatigue defect that was christened a squat was identified on the British railway network, primarily at first on the West Coast Main Line. Two productive decades of international research on squats followed, which later contributed to a rapid understanding of gauge corner cracking, which differs in detail but is similar in many important respects to a classic squat. In the last 10–15 years, a rail defect that is superficially similar to the classic squat has appeared on several railways. This has been investigated in some detail, initially in Australia and more recently also in Europe as part of the Innotrack project. These investigations have both assumed that the investigated defect is a classic squat. This paper reviews research on the squat and on its younger cousin. It forms the basis for a companion paper that presents original observations from track and detailed metallurgical examinations of specimens of the more recent squat-type defect. The review in this paper is used in the companion paper to identify features of the two types of defects that are similar and those that are significantly different.

Further developments in high-speed detection of rail rolling contact fatigue using ACFM techniques

The performance of existing ultrasonic and magnetic flux leakage techniques in detecting rail surface-breaking defects such as head checks and gauge corner cracking is inadequate during high-speed inspection, while eddy current sensors suffer from lift-off effects. Early detection of such rail defects is of paramount importance since a single crack can potentially lead to fatigue failure. The results obtained through rail inspection experiments under simulated conditions using an alternating current field measurement (ACFM) micro-pencil probe suggest that this technique can be applied for the accurate and reliable detection of surface-breaking defects at high inspection speeds.

Characterisation of defects in the railhead using ultrasonic surface waves

The ability to detect defects in rail, and in particular surface defects such as gauge corner cracking, is essential. Current ultrasonic testing of the rail uses contacting transducers in a send-receive mode which are at present limited in testing speed to around 20–30 mph, and signals from serious surface defects may be masked by nearby shallow surface defects. Using Rayleigh-like surface waves generated and detected in a pitch-catch manner we can overcome the effect of this masking, and by using electro-magnetic acoustic transducers (EMATs) working at a small standoff we may be able to lift many of the current rail testing speed limitations with a high accuracy for detecting and gauging surface defects. We present experiments on rail samples with real and machined defects, using EMATs to generate and detect a low-frequency wide-band surface wave. The depths of the defects can be characterised through analysis of both the time domain signal amplitude and frequency dependent behaviour. The design of EMAT used is discussed, with consideration of signal, frequency content, directionality of the signal and the effect of standoff above the sample.

Depth gauging of defects using low frequency wideband Rayleigh waves

In non-destructive testing for cracks it is not sufficient to simply detect the presence of a defect, but it is essential to have an accurate measure of the depth. Accurate calibration of the techniques used to gauge defect size is therefore necessary. Recent progress in the field of non-contact ultrasonic testing has led to the development of a practically viable system for generating and detecting wideband Rayleigh waves on electrically conducting or magnetic samples using electro-magnetic acoustic transducers (EMATs). This system has been used to gauge the depth and position of surface breaking defects, and has many applications including metal billet testing and detecting and sizing gauge corner cracking in rails. In this paper we report experiments calibrating the response of EMATs when a defect is present between the generator and receiver, using a calibration sample with slots machined perpendicular to the surface to simulate surface breaking cracks. The depth of the defect can be gauged in the time domain and frequency domain, with an accurate ‘fingerprint’ of the position given by an enhancement of the signal when the receiver is close to the defect. The best choice of EMAT design for different applications is discussed, as is the best position for the receive EMAT to avoid areas of interference between the Rayleigh wave and bulk waves diffracted from the crack tip.

Early warnings of the onset of rolling contact fatigue by inspecting the residual stress environment of the railhead

There is no method available to monitor localised stress levels on in-service railway track, although residual stresses in the rail crown have an important influence on the initiation and evolution of rolling contact fatigue (RCF) cracking. The MAPS technology has the ability to meet this need both in the short term with manual inspections and in the longer term with development of an inspection vehicle. This paper presents an update ( 2 ) of the MAPS measurement of stress levels and distributions in service rail but with a scope limited to specific studies into the early stages of rolling contact fatigue leading to gauge corner cracking. Data presented includes fine-scale stress distributions on rail cross-sections with RCF cracks together with stress distributions and stress depth profiles on rail heads, indicating both the earliest stages of rolling contact fatigue and established RCF cracking. The evidence suggests MAPS measurement data can act as indicators to the future emergence, presence and criticality of the RCF in rails, and thereby enhance maintenance regimes improving the safe service life of the rail network.